The document discusses different types of twins and their characteristics. It explains that identical or monozygotic twins develop from a single zygote that splits, so they are always genetically identical. Fraternal or dizygotic twins develop from two separate eggs fertilized by two separate sperm, so they are no more genetically similar than regular siblings. It also describes rare types of twins that can develop, such as semi-identical twins which are mostly but not fully identical.

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6. The output of the group ’ s effort on this enterprise may serve as a contribution to the existing body of instructional materials that the institution may utilize in order to provide effective and quality education. The lessons and evaluations presented in this module may also function as a supplementary reference for secondary teachers and students. ELVISON C. ALCANTARA Module Developer NEXT BACK CONTENTS

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8. The output of the group ’ s effort on this enterprise may serve as a contribution to the existing body of instructional materials that the institution may utilize in order to provide effective and quality education. The lessons and evaluations presented in this module may also function as a supplementary reference for secondary teachers and students. NEXT BACK CONTENTS FOR- IAN V. SANDOVAL Computer Instructor/ Adviser SANDRA P. MESINA Module Consultant LYDIA R. CHAVEZ Dean College of Education

9. The author wishes to acknowledge the following who gave him inspiration and strength to do this module: All the internet sites that helped the author to achieve broad information about the topic; Mr. For- Ian V. Sandoval, the author ’ s module adviser and Mrs. Sandra P. Mesina, the author ’ s module consultant for their constructive suggestions and criticism to improve the contents of this module; Mrs. Corazon San Agustin, dean of College of Education, Laguna State Polytechnic University for her untiring support, guidance and constant encouragement; The author ’ s family and friends who inspired him to accomplish this module; Lastly, to the Lord God Almighty who is the source of grace, wisdom and blessings for without his greatness this would not become possible. THE AUTHOR NEXT BACK CONTENTS

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12. NEXT BACK LSPU Vision, Mission, and Objectives i Objectives of BSEd ii Foreword iii Acknowledgement v Introduction vi General Objectives of Module vii Lesson 1: Twins 1 Table of contents viii Lesson 2: Multiple births 3 Lesson 3: Zygosity 8 Lesson 4: Identical twins (monozygotic) 14 Lesson 5: Fraternal twins (dizygotic) 18 Lesson 6: Common complication associated with multiples 22 Lesson 8: Common misconceptions 39 Lesson 9: Twin fun facts 42 References Lesson 7: Unique and unusual types of twin 18 About the Author

13. Fraternal twin (Dizygotic) Identical twin (Monozygotic) After the lesson, student is expected to: define twin; describe its characteristics; and support your understanding about twins. NEXT BACK CONTENTS

14. A twin is generally defined as one of two offspring produced in the same pregnancy and/or born at the same birth process, although people with unusually high genetical similarity also may be called twins although they may not be born at the same time (possibly by Caesarean section or surrogacy), such as with monozygotic (MZ, colloquially "identical") twins. Offspring that are not genetically identical but are born at the same time are called dizygotic (DZ, colloquially "fraternal" or "non-identical") twins. In contrast, the general term for more than one offspring in the same pregnancy (multiple birth s ) is multiples; a fetus which develops alone in the womb is called a singleton. NEXT BACK CONTENTS

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16. After the lesson, student is expected to: identify different risks among multiples; generalize multiple births; and accomplish the task after the lesson. Identical triplet brothers at graduation. Identical triplets are extremely rare, something that occurs only once in every 500,000 births. NEXT BACK CONTENTS

17. A multiple birth occurs when more than one fetus is carried to term in a single pregnancy. Common multiples are two and three, known as twins and triplets. These and other multiple births occur to varying degrees in most animal species, although the term is most applicable to placental species. Before the advent of ovulation-stimulating drugs, triplets were quite rare (approximately 1 in 8000 births) and higher order births so rare as to be almost unheard of. Multiple birth siblings are either monozygotic or dizygotic . The former result from a single fertilized egg or zygote splitting into two or more embryos, each carrying the same genetic material. Siblings created from one egg are commonly called identical. Since identical multiples share the same genetic material, they are almost always the same sex. In rare cases, however, a fertilized egg will have an extra gender typing chromosome. These fertilized eggs or zygotes can be XXX, XXY, or XYY. When a zygote with XXY or XYY splits you will end up with one XX and one XY twin who are genetically identical in every way but sex. NEXT BACK CONTENTS

18. Multiple pregnancies are usually delivered before the full term of 40 weeks gestation: the average length of pregnancy is around 37 weeks for twins, 34 weeks for triplets and 32 weeks for quadruplets. Their genetic similarity depends on the chromosome number in a species two parents can have genetically identical offspring without a zygote splitting. Humans have 23 chromosomes, so the chance of the offspring of the same human parents being identical (without being identical twins) is roughly equal to 1 in 2. It is statistically very improbable that two siblings will be genetically completely identical, but the level of similarly can become very high. The similarity between two offspring also depends upon the similarity of the genes of the parents. If the parents have any genes in common the probability of them being genetically identical is much improved. Dizygotic or fraternal multiples instead result from multiple ova being ripened and released in the same menstrual cycle by a woman's ovaries, which are then fertilized to grow into multiples no more genetically alike than ordinary full siblings. NEXT BACK CONTENTS

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20. Cerebral palsy Cerebral palsy is more common among multiple births than single births, being 2.3 per 1,000 survivors in singletons, 13 in twins, and 45 in triplets in North West England. Incomplete separation Multiples may become monochorionic, sharing the same chorion, with resultant risk of twin-to-twin transfusion syndrome. Monochorionic multiples may even become monoamniotic, sharing the same amniotic sac, resulting in risk of umbilical cord compression and entanglement. In very rare cases, there may be conjoined twins, possibly impairing function of internal organs. Mortality rate (stillbirth) Multiples are also known to have a higher mortality rate. It is more common for multiple births to be stillborn, while for singletons the risk is not as high. A literary review on multiple pregnancies shows a study done on one set each of octuplets, two sets of sextuplets, 8 sets of quintuplets, 17 sets of quadruplets, and 228 sets of triplets. NEXT BACK CONTENTS

21. By doing this study, Hammond found that the mean gestational age (how many weeks when birthed) at birth was 33.4 weeks for triplets and 31 weeks for quadruplets. The prenatal death rate for multiple births of more than six (sextuplets) was 100%. This shows that stillbirth happens usually 3 – 5 weeks before the woman reaches full term and also that for sextuplets or higher it almost always ends in death of the fetuses. Though multiples are at a greater risk of being stillborn, there is inconclusive evidence whether the actual mortality rate is higher in multiples than in singletons. Fertility therapy problems and selective reduction Today many multiple pregnancies are the result of fertility therapy. Elsner et al. studied 42 months of IVF (in vitro fertilization) procedures, and related the number of embryos transferred and the pregnancy outcome. In this time, they found that of the 2,173 embryo transfers performed, 734 were successfully delivered pregnancies (33.8%). These were analyzed … the overall multiple pregnancy rate was 31.3% (24.7% twins, 5.8% triplets, and .08% quadruplets)(8). NEXT BACK CONTENTS

22. This evidence shows that almost all of the births delivered were multiples rather than singletons, because IVFs are producing more multiples, a number of efforts are being made to reduce the risk of multiple births specifically triplets or more. Medical practitioners are doing this by limiting the number of embryos per embryo transfer to one or two. That way, the risks for the mother and fetuses are decreased. De Sutter et al. found by looking at a previous study done in 1997, that by using SET (single embryo transfer) the twin birth rate dropped from 30% to 21%. De Sutter et al. also found that the use of this transfer method increased from 1.5% to 17.5%(9). So limiting the number of embryos transferred can reduce the risks of having multiples and so reduce the risks associated with multiple pregnancies. Another procedure that the medical world is using today is known as selective reduction, i.e. the termination of one or more, but not all, of the fetuses. This is often done in pregnancies with multiple gestations to increase the likelihood that one child may live a healthy life. Armour et al. found by looking at a review of a series of 1000 selective reduction cases, it has had a loss rate of 5.4% in pregnancies. Many of the losses (15%) occurred within 4 weeks of the procedures and more than 50% occurred after 8 weeks. NEXT BACK CONTENTS

23. This shows that the reduction was successful at reducing the embryos from multiple gestations to single (9). Though selective reduction seems to be working, mothers of multiples who undergo this procedure are at a higher risk of miscarrying compared to that of an unreduced twin pregnancy. A study done by looking at 158 pregnant women who underwent selective reduction from higher order multiples to twins showed that the mother had a 10.6% chance of miscarriage. Mothers of twin pregnancies without reduction only had a 9.5% chance of miscarriage. Antsaklis et al. shows that there is a small increase in mortality for reduced twin pregnancies versus unreduced twin pregnancies. NEXT BACK CONTENTS

24. Birthing process and neonatal intensive care When it comes to the birthing process of multiples, mothers are more likely to receive a Caesarean (C-section) delivery than vaginal Michael Kogan et al. found that between 1989-1991 and 1995-1997 the cesarean delivery rate for mothers of multiples increased from 21.9% to 27%. Kogan et al. discovered this evidence by looking at the National Center for Health Statistics, births and infant death records for twins in the United States. Multiple-birth infants are usually admitted to neonatal intensive care immediately after being born. The records for all the triplet pregnancies managed and delivered from 1992-1996 were looked over to see what the neonatal statistics were. Kaufman et al. found from reviewing these files that during a five year period, 55 triplet pregnancies, which is 165 babies, were delivered. Of the 165 babies 149 were admitted to neonatal intensive care after the delivery. That is 90% of the babies born. NEXT BACK CONTENTS

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26. After the lesson, student is expected to: interpret zygosity; detect the common variations of twinning; and perform the task after the lesson. Zygosity is the similarity of alleles of a gene for a trait (inherited characteristic) in an organism. The DNA sequence of any gene can vary among individuals in the population. The various forms of a gene are called alleles, and diploid organisms generally have two alleles for each gene, one on each of the two homologous chromosomes on which the gene is present. In diploid organisms, the alleles are inherited from the individual's parents, one from the male parent and one from the female. Zygosity in general is a description of whether those two alleles have identical or different DNA sequences. NEXT BACK CONTENTS

27. There are five common variations of twinning. The three most common variations are all dizygotic: Male – female twins are the most common result, 50 percent of DZ twins and the most common grouping of twins. Female DZ twins (sometimes called sororal twins) Male DZ twins The other two variations are monozygotic twins: Female MZ twins Male MZ twins (least common) It is also the degree of identity in the genome of twins. NEXT BACK CONTENTS

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29. An individual that is homozygous dominant for a particular trait carries two copies of the allele that codes for the dominant trait. This allele, often called the "dominant allele", is normally represented by a capital letter (such as "P" for purple flowers, which are dominant in pea plants). When an organism is homozygous dominant for a particular trait, the genotype is represented by a doubling of the symbol for that trait, such as "PP". An individual that is homozygous recessive for a particular trait carries two copies of the allele that codes for the recessive trait. This allele, often called the "recessive allele" is usually represented by the lowercase form of the letter used for the corresponding dominant trait (such as, with reference to the example above, "p" for white flowers, which are recessive in pea plants). The genotype of an organism that is homozygous recessive for a particular trait is represented by a doubling of the appropriate letter, such as "pp". NEXT BACK CONTENTS

30. Heterozygous An organism is heterozygous for a particular gene when two different alleles occupy the gene's position on the homologous chromosomes. The cell or organism is called a heterozygote. Heterozygous genotypes are represented by a capital letter (representing the dominant allele) and a lowercase letter (representing the recessive allele), such as "Rr". The capital letter is usually written first. If the trait in question is determined by simple (complete) dominance, a heterozygote will express only the trait coded by the dominant allele and the trait coded by the recessive allele will not be present. In more complex dominance schemes the results of heterozygosity can be more complex. NEXT BACK CONTENTS

31. Hemizygous A diploid organism is hemizygous for a particular gene when only one allele for the gene is present. The cell or organism is called a hemizygote. Hemizygosity is observed when one copy of a gene is deleted, or in the heterogametic sex when a gene is located on a sex chromosome. For organisms in which the male is heterogametic, such as humans, almost all X-linked genes are hemizygous in males with normal chromosomes because they have only one X chromosome and few of the same genes are on the Y chromosome. In a more extreme example, male honeybees (known as drones) are completely hemizygous organisms. They develop from unfertilized eggs and their entire genome is haploid, unlike female honeybees, which are diploid. Transgenic mice generated through exogenous DNA microinjection of an embryo's pronucleus are also hemizygous, and can later be bred to homozygosity to reduce the need to confirm genotype of each litter. NEXT BACK CONTENTS

32. Nullizygous A nullizygous organism carries two mutant alleles for the same gene. The mutant alleles are complete loss-of-function or 'null' alleles, so homozygous null and nullizygous are synonymous. The mutant cell or organism is called a nullizygote. Researchers sometimes breed organisms to be nullizygous in a particular trait so that they can study how the organism is affected by the loss of the trait. Natural nullizygosity is very rare and can be fatal or extremely harmful to the individual since it prevents an entire trait from being expressed. NEXT BACK CONTENTS

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34. NEXT BACK CONTENTS Placental sharing May have one shared placenta, two separate placentas, or two placentas fused into one. May have two separate placentas or two placentas fused into one. May have two separate placentas or two placentas fused into one. Genetic markers Share 100% of their genetic markers. Share about 50% of their genetic markers, same as singleton siblings. Share about 75% of their genetic markers, more than fraternal but less than identical. Gender Are always same sex. May be same sex or male/female. May be same sex or male/female. Blood type Have the same blood type. May have the same blood type or different. May have the same blood type or different. Causes Not caused by fertility treatments, birth control pills or maternal age. No one knows what causes identical twinning. Can be attributed to fertility treatments, advanced maternal age, birth control pills or other factors that influence twinning. No one knows what causes this type of twinning to occur.

35. NEXT BACK CONTENTS Sac in uterus May be contained in one sac in utero. Develop separate sacs in utero. Develop separate sacs in utero. Complication/s Can result in conjoined twins or mirror image twins. Not conjoined. Not conjoined. Risks May be at risk for Twin-to-Twin Transfusion Syndrome (TTTS) Rarely at risk for TTTS. Rarely at risk for TTTS.

36. Complete the table: Zygosity Chart for Multiples NEXT BACK CONTENTS Basis Monozygotic Twins Dizygotic Twins Polar Body Twins Formation 1. Form when two eggs are fertilized by two separate sperm. 2. Placental sharing May have one shared placenta, two separate placentas, or two placentas fused into one. 3. May have two separate placentas or two placentas fused into one.

37. NEXT BACK CONTENTS Genetic markers 4. Share about 50% of their genetic markers, same as singleton siblings. Share about 75% of their genetic markers, more than fraternal but less than identical. Gender Are always same sex. 5. 6. Blood type 7. 8. May have the same blood type or different. Causes Not caused by fertility treatments, birth control pills or maternal age. No one knows what causes identical twinning. Can be attributed to fertility treatments, advanced maternal age, birth control pills or other factors that influence twinning. 9. Complication/s Can result in conjoined twins or mirror image twins. 10. Rarely at risk for TTTS.

38. Briefly discuss each type of zygosity of twins. Homozygous- ___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________. Heterozygous- ___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________. Hemizygous- ___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________. NEXT BACK CONTENTS

39. What are the five common variations of twinning? _______________________ _______________________ _______________________ _______________________ _______________________ Nullizygous- ___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________. NEXT BACK CONTENTS

40. After the lesson, student is expected to: define identical twin; be familiar with this type of twin; and appreciate the identical twin. Identical twins form when a single fertilized egg splits into two genetically identical parts. The twins share the same DNA because they were originally from the same fertilized egg. Because identical twins share exactly the same DNA, they will often look very similar. However, environmental factors also play a role in development and sometimes, identical twins may look very different even though they have exactly the same DNA. NEXT BACK CONTENTS

41. Environmental conditions both inside the womb and throughout their lives influence the switching on and off of various genes. Division of the zygote into two embryos is not considered to be a hereditary trait, but rather an anomaly that occurs in birthing at a rate of about three in every 1000 deliveries worldwide, regardless of race. Monozygotic twins are genetically identical (unless there has been a mutation during development) and they are almost always the same sex. On rare occasions, monozygotic twins may express different phenotypes, normally due to an environmental factor or the deactivation of different X chromosomes in monozygotic female twins, and in some extremely rare cases, due to aneuploidy, twins may express different sexual phenotypes, normally due to an XXY Klinefelter's syndrome zygote splitting unevenly). Monozygotic twins look alike, although they do not have the same fingerprints (which are environmental as well as genetic). As they mature, MZ twins often become less alike because of lifestyle choices or external influences. Genetically speaking, the children of MZ twins are half-siblings rather than cousins. It is estimated that there are around 10 million monozygotic twins and triplets in the world. NEXT BACK CONTENTS

42. The likelihood of a single fertilization resulting in MZ twins appears to be a random event, not a hereditary trait, and is uniformly distributed in all populations around the world. This is in marked contrast to DZ twinning, which might mainly be due to IVF (in vitro fertilization). The exact cause for the splitting of a zygote or embryo is unknown. Monozygotic twins have nearly identical DNA, but differing environmental influences throughout their lives affect which genes are switched on or off. This is called epigenetic modification. A study of 80 pairs of human twins ranging in age from three to 74 showed that the youngest twins have relatively few epigenetic differences. Twins who had spent their lives apart (such as those adopted by two different sets of parents at birth) had the greatest difference . However, certain characteristics become more alike as twins age, such as IQ and personality. This phenomenon illustrates the influence of genetics in many aspects of human characteristics and behavior. A recent theory posits that monozygotic twins are formed after a blastocyst essentially collapses; splitting the progenitor cells (those that contain the body's fundamental genetic material) in half. That leaves the same genetic material divided in two on opposite sides of the embryo. Eventually, two separate fetuses develop. NEXT BACK CONTENTS

43. The stereotype of identical twins is that they are exactly alike: they look alike; they dress in matching outfits, share the same likes and dislikes. Parents of identical twins know differently, however. Despite their shared genetic component, identical multiples are unique individuals. Though they do share similarities, they also have many differences. For example, children have always exhibited about a twenty-five percent difference in their weight. When they were newborns, weighing four and five pounds, it was quite obvious. At other times as they've grown up, it's not noticeable. They have confirmed that they are indeed identical twins, yet people are often skeptical because they don't "look" alike. They don't act alike either. One likes to dance; the other likes to play basketball. Certainly, we encourage them to pursue their individual interests, but the initial inclination towards these activities were all their own. NEXT BACK CONTENTS

44. Environmental Differences While identical twins form with the same set of genes, human development is not just genetic. The environment also has an impact. So, beginning in the early environment of the womb, external influences can change the appearance of twins. For example, some monozygotic twins share a placenta. One twin may have a more advantageous connection to the placenta, receiving the first run of nutrients. This situation can cause a size discrepancy between the babies, a physical difference that continues as they grow up. Twin-to-Twin Transfusion Syndrome (TTTS) is another condition that affects twins in the womb, and can impact their development. While most twins grow up in the same home environment, there are many circumstances that create differences in the children appearances, personalities, and interests. As the twins approach the teen years, they may even seek to establish dissimilar qualities in order to establish individual identities. NEXT BACK CONTENTS

45. Epigenetic Differences Scientists have offered a new explanation for the differences between identical twins. Epigenome refers to natural chemical modifications within a person's genome (genetic material). As an article in the New York Times explains, they "act on a gene like a gas pedal or a brake, marking it for higher or lower activity." A study conducted by a team of researchers at the Spanish National Cancer Center in Madrid concluded that, while identical twins are born with the same epigenome, their epigenetic profiles begin to diverge as they age. The differences increase as twins live longer and spend more time apart. The scientists offered two theories to explain this phenomenon. First, that epigenetic marks are removed randomly as people age. Secondly, environmental influences change the pattern of epigenetic marks. NEXT BACK CONTENTS

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47. After the lesson, the student is expected to: define fraternal twin; understand this type of twin; and perform the task after the lesson. A twin pregnancy most commonly occurs when two separate eggs are fertilized by separate sperm to form two zygotes. Each zygote implants in the uterus individually and develops its own membranes and placenta. The two zygotes continue to develop as two separate embryos. These twins are referred to as dizygotic (commonly known as fraternal) twins. NEXT BACK CONTENTS

48. The genetic connection of fraternal twins is no more or less the same as siblings which are born at separate times. Fraternal twins may be the same or different sexes, and they may look similar to each other or they may look very different. Fraternal twins, like any other siblings, have an extremely small chance of having the same chromosome profile. Studies show that there is a genetic basis for DZ twinning. However, it is only their mother that has any effect on the chances of having DZ twins; there is no known mechanism for a father to cause the release of more than one ovum. NEXT BACK CONTENTS

49. Maternal history of twinning It is believed that hereditary dizygotic twinning may be transmitted as a recessive trait [16] or as an autosomal dominant female-specific trait with limited expression. NEXT BACK CONTENTS

50. "The probability of a subsequent twin pregnancy is increased 4-fold in mothers of twins, and the risk of having dizygotic twins is roughly doubled for women whose mother or sister has dizygotic twins ". High follicular follicle-stimulating hormone level may explain the hereditary tendency for multiple ovulation and pregnancy in some families. Multiparity The risk of having dizygotic (fraternal) twins is increased in women with several previous pregnancies. High body mass index and height. The odd of dizygous twinning is greater among women very tall women and in women with a pre pregnant body mass index (BMI) of 30 or more. NEXT BACK CONTENTS

51. DIZYGOTIC TWINS PLACENTAL TYPES Dichorionic (two placentas), Diamniotic (two amnions) Dizygotic (fraternal) twins develop in two separate amniotic sacs (bag of water) and will have their own, separate, placentas. However, the placentas may at times appear to be fused. NEXT BACK CONTENTS

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53. Fused Placenta Separate Placenta Draw : Dizygotic twins ’ placental types. NEXT BACK CONTENTS

54. After the lesson, the student is expected to: determine the different complication associated to multiples; accept twins with abnormalities; and draw from memory the common complications among multiples. A single placenta normally supports a single fetus. When the situation arises in which two fetuses have to share a single placenta, complications may sometimes develop. Identical twins that share a single placenta are called monochorionic twins (MC). “Chorion” is the Latin root that refers to the placenta, while the word “amnion” refers to the sac, or “membranes” that surround each fetus. While fraternal twins (2 eggs and 2 sperm) are always surrounded in their own sacs and have their own individual placentas, 70% of identical twins may end up sharing a single placenta. Only 1% of identical twins share both a single placenta and a single sac, and this poses significant risk. NEXT BACK CONTENTS

55. When two fetuses share one placenta, their umbilical cords may implant anywhere – there is no set or predictable pattern – and depending on where they implant, one fetus may get less of a ‘share’ of the placenta than its co-twin, resulting in less blood flow and nutrition to one fetus, with more to the other (unequal placental sharing). As a result, although identical twins usually share the same genetic material, they may actually grow differently. Like the roots of a tree, the blood vessels that run from each implanted cord may connect with each other beneath the surface, as there is nothing separating them within a single placenta. Depending on which types of vessels connect to which, one fetus may transfuse blood to the other. We will discuss each of these complications, their risks, below. NEXT BACK CONTENTS

56. A picture of conjoined twin connected in their chest When the division of the developing zygote into 2 embryos occurs, 99% of the time it is within 8 days of fertilization. If the division of the zygote occurs later than the 8 days then conjoined twins are usually the result. Conjoined twins form exactly like identical twins, but at some point during the stage where the single egg splits, the process stops, and the twins develop attached to one another. This occurs in about 1 out every 100,000 to 200,000 live births, but 60% of conjoined twins are either stillborn or lost in utero. Mortality is highest for conjoined twins due to the many complications resulting from shared organs. NEXT BACK CONTENTS

57. How They Are Formed? Conjoined twins are genetically identical, and are, therefore, always the same sex. They develop from the same fertilized egg, and they share the same amniotic cavity and placenta. Twinning occurs one of two ways: either a woman releases two eggs instead of the usual one or she produces only one egg that divides after fertilization. If she releases two eggs, which are fertilized by separate sperm, she has fraternal twins. When a single, fertilized egg divides and separates, she has identical or paternal twins. In the case of conjoined twins, a woman only produces a single egg, which does not fully separate after fertilization. The developing embryo starts to split into identical twins during the first few weeks after conception, but stops before the process is complete. The partially separated egg develops into a conjoined fetus. NEXT BACK CONTENTS

58. Types of conjoined twins Conjoined twins are typically classified by the point at which their bodies are joined. The most common types of conjoined twins are: Thoraco-omphalopagus (28% of cases): Two bodies fused from the upper chest to the lower chest. These twins usually share a heart, and may also share the liver or part of the digestive system. Thoracopagus (18.5%): Two bodies fused from the upper thorax to lower belly. The heart is always involved in these cases. Omphalopagus (10%): Two bodies fused at the lower chest. Unlike thoracopagus, the heart is never involved in these cases; however, the twins often share a liver, digestive system, diaphragm and other organs. Parasitic twins (10%): Twins that are asymmetrically conjoined, resulting in one twin that is small, less formed, and dependent on the larger twin for survival. Craniopagus (6%): Fused skulls, but separate bodies. These twins can be conjoined at the back of the head, the front of the head, or the side of the head, but not on the face or the base of the skull. NEXT BACK CONTENTS

59. Other less-common types of conjoined twins include: Cephalopagus : Two faces on opposite sides of a single, conjoined head; the upper portion of the body is fused while the bottom portions are separate. These twins generally cannot survive due to severe malformations of the brain. Also known as janiceps (after the two-faced god Janus) or syncephalus. Synecephalus : One head with a single face but four ears, and two bodies. Cephalothoracopagus : Bodies fused in the head and thorax. In this type of twins, there are two faces facing in opposite directions, or sometimes a single face and an enlarged skull. Xiphopagus : Two bodies fused in the xiphoid cartilage, which is approximately from the navel to the lower breastbone. These twins almost never share any vital organs, with the exception of the liver. A famous example is Chang and Eng Bunker. Ischiopagus : Fused lower half of the two bodies, with spines conjoined end-to-end at a 180° angle. These twins have four arms; two, three or four legs; and typically one external set of genitalia and anus. NEXT BACK CONTENTS

60. Omphalo-Ischiopagus : Fused in a similar fashion as ischiopagus twins, but facing each other with a joined abdomen akin to omphalopagus. These twins have four arms, and two, three, or four legs. Parapagus : Fused side-by-side with a shared pelvis. Twins that are dithoracic parapagus are fused at the abdomen and pelvis, but not the thorax. Twins that are diprosopic parapagus have one trunk and one head with two faces. Twins that are dicephalic parapagus have one trunk and two heads, and two (dibrachius), three (tribrachius), or four (tetrabrachius) arms. Craniopagus parasiticus : Like craniopagus, but with a second bodiless head attached to the dominant head. Pygopagus (Iliopagus) : Two bodies joined back-to-back at the buttocks. NEXT BACK CONTENTS

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62. Monozygotic twins who share a placenta can develop twin-to-twin transfusion syndrome. This condition means that blood from one twin is being diverted into the other twin. One twin, the 'donor' twin, is small and anemic, the other, the 'recipient' twin, is large and polycythemic. The lives of both twins are endangered by this condition. Twin to Twin Transfusion Syndrome is a condition that only affects identical twins that share one placenta (monochorionic). Doctors’ estimate there is up to a 25% chance of such a pregnancy resulting in twin to twin transfusion syndrome. Male and female identical twins are affected equally, since the causes of the syndrome are not based on genetic problems, but on the actual development of the placenta. When twins are affected by TTS, the blood flow through the placenta begins to "favor" one twin over the other. The twin who pumps blood for both twins and as a result whose blood supply is compromised is called the "donor" twin and the twin who receives too much blood is called the "recipient" twin. NEXT BACK CONTENTS

63. The twin who filters all of the blood for both twins (the "donor" twin) usually becomes smaller, and loses amniotic fluid because he/she isn't urinating properly into the amniotic sac. This twin also does not develop well, because all of its energy goes into the blood filtering process. The twin who receives too much blood (the "recipient" twin) usually becomes larger, but undergoes stress because he/she is developing too quickly, too much blood is traveling through his/her body, and his/her amniotic fluid is excessive. TTS can occur at any time in the pregnancy, and different risks are associated with different diagnostic times. If TTS is diagnosed early in the pregnancy, the babies cannot be delivered. If it occurs late in the pregnancy, the babies may be delivered early, but will still be at risk for certain complication. NEXT BACK CONTENTS

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69. A picture of caesarean section NEXT BACK CONTENTS

70. A fetus papyraceus shown with its umbilical cord next to the placenta of its dichorionic diamniotic twin. Researchers suspect that as many as 1 in 8 pregnancies start out as multiples, but only a single fetus is brought to full term, because the other has died very early in the pregnancy and has not been detected or recorded. Early obstetric ultrasonography exams sometimes reveal an "extra" fetus, which fails to develop and instead disintegrates and vanishes. This is known as vanishing twin syndrome. Some experts estimate that 1/5 to 1/3 of all multiple pregnancies involve a vanishing twin. While this number can seem high, it should be noted that many pregnancies that result in a vanishing twin are never diagnosed as a multiple pregnancy; indeed, the mother many never know she was carrying more than one baby. NEXT BACK CONTENTS

71. Since the advent of ultrasound, many more doctors and women are aware that a multiple pregnancy exists much earlier than in the past. When vanishing twin syndrome occurs in the first trimester, there is little effect on the mother or the surviving fetus. However, when the twin vanishes in the second or third trimester, there is a higher likelihood of effect on the other fetus, such as a higher incidence of cerebral palsy. Most vanishing twins are reabsorbed into the placenta or be compressed by the pressure of the remaining fetus and its amniotic sac. If the placenta is analyzed, evidence can sometimes be found of another DNA profile, which indicates the vanishing twin existed. NEXT BACK CONTENTS

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73. A picture of a child with his parasitic twin connected in his abdomen Sometimes one twin fetus will fail to develop completely and continue to cause problems for its surviving twin. One fetus acts as a parasite towards the other. Sometimes the parasitic twin becomes an almost indistinguishable part of the other, and sometimes this needs to be medically dealt with. NEXT BACK CONTENTS

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75. Xiphopagus Parapagus Craniopagus parasiticus Pygopagus Synecephalus Parasitic twins Craniopagus Thoracopagus Cephalothoracopagus Cephalopagus Omphalopagus Ischiopagus Thoraco-omphalopagus Omphalo-Ischiopagus NEXT BACK CONTENTS

76. True or False: Draw a star if the statement is correct and draw a box if not. 1. Conjoined twins are genetically identical, and are, always the same sex.______ 2. Partial molar twins a very rare type of parasitic twinning is one where a single viable twin is endangered when the other zygote becomes cancerous, or molar. ______ 3. Monozygotic twins who share a placenta cannot develop twin-to-twin transfusion syndrome. ______ 4. Most vanishing twins are reabsorbed into the placenta or be compressed by the pressure of the remaining fetus and its amniotic sac. If the placenta is analyzed, evidence can sometimes be found of another DNA profile, which indicates the vanishing twin, existed. ______ 5. Preterm labor/delivery is defined as delivery before 27 completed weeks of pregnancy. ______ 6. Twins can be delivered vaginally when the gestation is greater than 39 weeks. ______ 7. The increased risk for gestational diabetes in a multiple pregnancy appears to be a result of the two placentas increasing the resistance to insulin, decreased placental size, and an elevation in placental hormones. ______ 8. Low birth weight is almost always related to preterm delivery. Low birth weight is less than 10.5 pounds. _______ 9. wins can be delivered vaginally when twin A (the baby closest to the cervix) is the largest. ______ 10. Parasitic twins are developed when one twin fetus will fail to develop completely and continue to cause problems for its surviving twin. One fetus acts as a parasite towards the other. ______ NEXT BACK CONTENTS

77. List the common complications associated with multiples. NEXT BACK CONTENTS

78. After the lesson, the student is expected to: understand the unique and unusual type of twin; balance the different types of twin; and accomplish the task after the lesson. NEXT BACK CONTENTS

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86. Use your answer in the first activity then hunt those words inside the puzzle. Encircle your answer. NEXT BACK CONTENTS E G T D A V G J H T C O N J O I N E D G F G T P J T W I N S W I T H D I F F R E N T B I R T H D A Y A G I X S T I C K P A R T Y Y H E S G O K I L R L S U P E R F E T A T I O N F N M D I E N I C T A K T W I S N F S E M I I D E N T I C A L T W I N S H R A L D P Y D B O S N I W T E G A M I R O R R I M M E X E P O L A R B O D Y T W I N S Z A P O Y T E R P O X A S D E K L A N R E T A P O R E T E H I N F T W I N S O F D I F F E R E N T R A C E S A C J G D V M O I N O S I V L E O A E R A N G E H G K L

87. After the lesson, the student is expected to: recall the common misconceptions about twins; discuss each misconception; and perform the task after the lesson. After the main classifications, common complications, and unusual type of twins, you are thinking that you already know everything about twins but not that fast. Here are another bunch of trivia that I know you will love. Most of us think of something about twins but the truth is, it is not true. NEXT BACK CONTENTS

88. 1. All Twins Share the Same Birthday It is possible for twins to have different birthdates. The most common reason is when one is born before midnight and their sibling is born after. There have also been cases when one baby has been delivered while the other remained in the womb for several days for medical reasons. 2. All Twins Have the Same Parents I know what you are thinking … .But it really is possible. This actually does happen! The twins must be fraternal because, as explained earlier, identical twins are formed from one egg and one sperm. However, fraternal twins are formed from 2 separate eggs and sperm. Therefore, it is entirely possible for a woman to have intercourse with 2 separate companions within the same ovulation cycle and thus producing fraternal twins. NEXT BACK CONTENTS

89. 3. Twins Can Feel Each Other ’ s Pain It is true that this does happen, but not all twins have this ability. This isn ’ t really anything supernatural though. It is more easily explained by the close bond that some twins share. This type phenomenon is not limited to twins by any means. 4. All Twins Dress Alike This really depends on the individuals. Their mother can dress them alike, but as they get older they will most likely choose to dress differently for the most part. The majority of twins will find themselves trying to distinguish themselves from their sibling to establish their own identities. NEXT BACK CONTENTS

90. 5. Twins Have a Secret Language About 40% of twins will develop a “ secret language ” using gestures, abbreviations, nicknames, etc that they only use when talking to each other. A parent or other sibling can usually pick up on it eventually. However, the twins generally don ’ t communicate in this way with others. It should be noted that twins often experience delays in language development. There are a few different reasons for this. Normally, babies learn language from their parents or caregivers, but parents of twins sometimes find themselves spread a little thin. Imagine that! Premature birth could also be a factor. Also, twins spend a lot of time together. Therefore, like any 2 people that spend a substantial amount of time together, they may learn to rely on shorthand or nonverbal forms of communication. This can delay their need to express themselves through conventional language. There are a few things a parent can do to help. NEXT BACK CONTENTS

91. 1._____Fraternal twins are formed from 2 separate eggs and sperm. Therefore, it is entirely possible for a woman to have intercourse with 2 separate companions within the same ovulation cycle and thus producing fraternal twins. 2._____About 40% of twins will develop a “ secret language ” using gestures, abbreviations, nicknames, etc that they only use when talking to each other. 3._____This really depends on the individuals. Their mother can dress them alike, but as they get older they will most likely choose to dress differently for the most part. 4._____It is true that this does happen, but not all twins have this ability. This isn ’ t really anything supernatural though. It is more easily explained by the close bond that some twins share. NEXT BACK CONTENTS

92. Twins’ secret language b. All twins dress alike c. Twins’ each other’s pain d. Twins’ the same parents e. Twins’ the same birthday 5._____The most common reason of this is when one is born before midnight and their sibling is born after. There have also been cases when one baby has been delivered while the other remained in the womb for several days for medical reasons. NEXT BACK CONTENTS

93. After the lesson, the student is expected to: combine the different fun facts about twins; accumulate the twin fun facts; and accomplish the task after the lesson. First Test Tube (IVF) Twins The world's first test tube twins are Stephen and Amanda Mays born June 5 1981. Youngest Mother of Twins The youngest mother of twins is Donna Dowman of England, conceived twins at 13 and had Rachel and Rebecca at age 14 in 1997. Nicola Doherty of England had her twins Courteney and Caitlyn April 20 1997 when she was 14. NEXT BACK CONTENTS

94. Youngest Father of Twins The youngest father of twins is James Sutton of England, who was 13 when his girlfriend Sarah Drinkwater (age 17) had identical twins Leah and Louise in late 1999. Oldest Mother and Father of Twins, the oldest mother of twins is Lin Fu-mei of Taiwan, who apparently had twins at age 59. Judy Cates of the USA had twins at age 58. Lynne Bezant of England had twins David and Susan on May 24 2001 at age 56. Marilyn Nolen had twins Travis and Ryan on March 22 2000 at age 55. The World's Oldest Triplets Who Ever Lived The longest-lived triplets ever recorded were Faith, Hope, and Charity Cardwell (USA) who were born on May 18, 1899. Faith died first on October 2, 1994 age 95 years 137 days. The World's Oldest Living Triplets Marjory Skeaping (neé Scott), Sheila Botterill (neé Scott), and David Scott (UK) have been verified as the world's oldest living triplets. They were born in Edinburgh, SCOTLAND on May 19, 1920. Curiously, their Uncle, Aunt, and their Mother's First Cousin also celebrate their birthdays on May 19th. NEXT BACK CONTENTS

95. The World's Oldest Living Quadruplets The oldest quadruplets were The Ottmans (GERMANY). Adolf, Ann-Marie, Emma, and Elisabeth were born on May 5, 1912. All four quads lived to the age of 79. In November 2000, there were 992 sets of quadruplets worldwide. Identical quads are quite rare - only about 20 sets worldwide. Longest time a twin has remain undiscovered** 7/97 - a fetus was discovered in the abdomen of a 16 year old - Hisham Ragab of Egypt. A swollen sac found pressing against his kidney turned out to be his 7 inch long, 4lb, 6oz identical twin. Longest Lived Conjoined Twins** Chang & Eng Bunker from Siam (now Thailand). They were born 5/11/1811 and they passed away within 3 hours of each other at the age of 63 on 1/7/1874 NEXT BACK CONTENTS

96. Ronnie & Donnie Gaylon are the oldest living male conjoined twins. They are 47 years old and live in Ohio. For 36 years they traveled in shows, carnivals and the circus. They retired in 1991. Heaviest Twins** Billy and Benny Crary - Hendersonville, NC They were normal in size until they were 6 years old. In 1978 Billy was 743 pounds and Benny was 723 pounds. Their waist measurement was 7 ft. Largest Multiple Birth** 1971 - Dr Gennaro Montanino from Rome-Italy, claimed to have removed 15 fetuses from the uterus of a 35yr old woman after 4 months of pregnancy. A fertility drug was responsible for these Quindecaplets. NEXT BACK CONTENTS

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98. Conjoined twins are genetically identical and are, therefore, always the same sex. They develop from the same fertilized egg. One of the earliest documented cases of conjoined twins was Mary and Eliza Chulkhurst. They were born in Biddenden, Kent , England , in the year 1100, and were joined at the hip. Another set of famous conjoined twins was Eng and Chang Bunker, who were born in Thailand (then called Siam) in 1811. The term Siamese twin was coined as a reference to Eng and Chang, who achieved international fame shortly after leaving Siam as teenagers. They were exhibited in circus shows around the world before settling in the United States, where they married two sisters and had nearly two dozen children. They were 63 years old when they died. The term “Siamese twins” is no longer considered appropriate. Conjoined twins aren't limited to any racial or ethnic group and have been born all over the world. NEXT BACK CONTENTS

99. List here you have found: 1. _____________________ 2. _____________________ 3. _____________________ 4. _____________________ 5. _____________________ NEXT BACK CONTENTS

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101. http://www.motheroftwins.com/factsabouttiwns.html.December 31, 2010 http://multiples.about.com/cs/funfacts/a/multiplemyths.htm .December 31, 2010 http://multiples.about.com/od/pregnancy/a/genderselect.htm.December 31, 2010 http://multiples.about.com/cs/funfacts/a/oddsoftwins_2.htm.December 31, 2010 http://multiples.about.com/od/funfacts/Fun_Facts_Statistics_and_Trivia_About_Twins_and_Multiples.htm.December 31, 2010 http://multiples.about.com/od/funfacts/a/differenttwins.htm.December 31, 2010 http://psychic abilities.suite101.com/article.cfm/telepathy_identical_twins#ixzz0alPAw5Jp . January 01, 2010 www.blessedwithtwins.com/All_About_Twins.January 01, 2010 http://www.keepkidshealthy.com/twins/expecting_twins.html.January 001, 2010 www.twinship.com.January 01, 2010 http://multiples.about.com/od/funfacts.January 01, 2010 http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Twins_identical_and_fraternal?open.January 01, 2010 http://multiples.about.com/cs/funfacts/l/aa060101b.htm.January 01, 2010 NEXT BACK CONTENTS

102. Pictures came from: URL http://multiples.about.com/od/picturesphotos/ig/Baby-Boy-Girl-Twins-Gallery/blgal1016.htm .February 14, 2010 http://multiples.about.com/od/picturesphotos/ig/Baby-Boy-Girl-Twins-Gallery/blgal690.htm .February 14, 2010 http://www3.ha.org.hk/pwh/content/pwh/Obstetrics%20and%20Gynaecology/img/10_02.jpg.February 14, 2010 http://multiples.about.com/od/picturesphotos/ig/Twin-Ultrasound-Photo-Gallery/blgalus18.htm.FEbruary 14, 2010 greenpeace.org science.qj.net blog.wired.com purestrange.wordpress.com clipartof.com myhealthinsight.com lifespan.org teachline.ls.huji.ac.il animate4.com brewsterschools.org flatrock.org.nz flickr.com pregnancy-bliss.co.uk estatevaults.com multiples.about.com visit-chiangmai.com celebritybabies.info NEXT BACK CONTENTS

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