Types of twins and complications during pregnancy

2.  Twins-two off springs produced by the same
pregnancy.
 The two babies born at the time for a mother.
 Twins are due to multiple pregnancy.
 The early cells of the mammalian embryo can
replace each other and compensate for a
missing cell.
 This regulative ability was first demonstrated in
1952, when Seidel destroyed one cell of a 2-
cell rabbit embryo and the remaining cell
produced an entire embryo.

3.  The regulative capacity of the ICM
blastomeres is also seen in humans.
 Human twins are classified into two
major groups:
Monozygotic twins
Dizygotic twins

4.  Monozygotic twins are otherwise called
as identical twins.
 They are extremely similar in their
characters.
 Develop from single zygote
 During cleavage, the zygote divides into
two blastomeres.
 These blastomeres separate and each
develops into a baby.

6.  The two babies are similar in all
respects.
 Same sex.
 Same type of genes.
 Same type of blood group.
 They are generally opposite handed.
 They show similar whirls of hair on the
head but in a reverse order like mirror
image.

7.  Due to the arrangement of placenta and
membranes it is divided into 4 types
 These types depends on division of
zygote.
Dichorionic diamniotic twins
Monochorionic diamniotic twins
Monochorionic monoamniotic twins
conjoined twins

9.  Where each twin has its own chorionic
and amniotic sacs.
 This type occurs most commonly with
dizygotic twins but may also occur with
monozygotic twin pregnancies.
 This type of pregnancy may have
characteristic findings on ultrasound.

10.  This type of twins are the product of a
single fertilized ovum, resulting in
genetically identical offspring.
 They share a single placenta but have
separate amniotic sacs.
 The occurrence of this type of twins
occurs at a rate of three to four in 1,000
live birth.

11.  They are the monozygotic multiples.
 They share a single amniotic and single
placenta.
 But they have separate umbilical cord.
 This case is very rare and may cause
risk to the babies due to cord
entanglement.

12.  Conjoined twins also known as siamese
twins.
 They are identical twins that have not split
properly after fertilization.
 They share body and may share vital
organs.
 Separation of conjoined twins is usually
performed at a very young stage.
 In some cases the brain or the heart must
be separated in order to provide each twin
with vital organs.

13.  Dizygotic twins are otherwise called as
fraternal twins.
 Fraternal twins are like ordinary brothers
and sisters.
 Develop from two independent zygote.
 So they are called as dizygotic twins.
 Formed by the fertilization of two eggs by
two sperms.
 They may be of same sex or opposite sex.
 Different genotypes.

15.  Dissimilar characters.
 They are called as non-identical twins.
 If both eggs are fertilized by the X-
chromosome female babies are produced.
 If both the eggs are fertilized by the Y-
chromosomes male babies are produced.
 If one egg is fertilized by X carrying sperm
and another by Y carrying sperm male and
female babies are produced.

16.  2 to 3 fold increased than singletons.
 Threatened and spontaneous abortion.
 Severe anemia
 Hypertensive disorders of pregnancy.
 Gestational diabetes.
 Operative delivery
 Increased maternal mortality.

17.  Congenital malformations
 Low birth weight
 Preterm birth
 Monochrionic pregnancy complications
 Perinatal asphyxia
 Fetal death
 Cord accidents
 Increased perinatal mortality.

18.  Monoamniotic twins – 1 in 20
monochorionic twins are monoamniotic
 Associated with high fetal death rate
from cord entanglement, congenital
anomalies, preterm birth or twin-twin
transfusion syndrome
 Diamniotic twins can become
monoamniotic if the dividing membrane
ruptures.

19.  External parasitic twins- grossly defective
fetus or merely fetal parts attached
externally to a relatively normal twins.
 Believed to result from demise of the
defective twin with its surviving tissues
attached to and vascularised by its normal
twin.
 Fetus in early development one embryo
may be enfolded within its twin
 Classically vertebral or axial bones are
found in these fetiform mases supported by
their host by a few large parasitic vessels.

20.  Two amniotic sacs and a common
surrounding chorion.
 Anatomical sharing of the two fetal
circulations through anastomoses of
placental arteries and veins.
 Artery to artery anastomoses are most
common and are identified on the
chorionic surface of the placenta-75%
 Vein to vein and artery to vein -50%

21.  Deep artery to vein connections can extend
from capillary bed of a given villus creating
a common villous compartment or third
circulation.
 Depending on the degree to which they are
hemodynamically balanced severity
occurs.
 With significant pressure or flow gradients
a shunt will develop between fetuses.
 Chorionic feto fetal transfusion results in
several clinical syndromes.

22.  5-17% of monochorionic twin
 Blood is transfused from donor twin to
its recipient sibling- donor is anemic and
growth may be restricted.
 Recipient become polycythemic, with
circulatory overload and may manifest
as hydrops.
 Deoxygenated blood from donor
placental artery pumped into a cotyledon
shared by recipient.

25.  Once oxygen exchange is completed in
the chorionic villus, oxygenated blood
leaves the cotyledon via a placental vein
of the recipient twin.
 Clinically important TTTs is frequently
chorionic, results from significant volume
differences.

27.  It is a condition in which presence of two
or more chromosomal complements
found in the same tissue of an
individual.
 The divergent genotypes are usually
found in all across the genome.
 It occurs in single organism composed
of cells with distinct genotype.
 Chimeras can happen with organ
transplantation.

29.  Natural chimerism
 Organism with mixed sexual
characteristics.
 May occur when two fertilized eggs fuse
together.
 SRY genes gets transferred to the X
chromosome during meiosis.
 Organism developed are known as
hermaphrodite.

30.  Occurs due to fertilization of an oocyte
and its second polar body by two
sperms.
 Also occur when a zygote fuses with a
fertilized polar body.
 The organism developed from the
zygote consist both type of genetic
materials.

32.  It is the presence of
two genetically distinct
and separately derived
populations of cells.
 One population being
at a low concentration
than other.
 The cells genetically
distinct from those of
the host individual.
 Usually occurs to
foetus from mother.

33.  Occurs due to
fertilization of two
separate ova by two
sperm, followed by
aggregation of the
two at the blastocyst
or zygote stages.
 Organism with
intermingled cell
lines.
 Organism developed
possess organs that
have different sets of
chromosomes.

35.  Usually found in Angler fish.
 The male releases an enzyme that digests
the skin of his mouth and the body of the
male
 Formation of single hermaphroditic
individual takes place
 The male develops large testicles and
atrophy of other organs take place.
 Becomes able to have a great number of
offsprings.

36.  Occurs when the germ cells of an
organism are not genetically identical to
its own.
 Mainly found in marmosets
 They carry the reproductive cells of their
fraternal twin siblings
 Occurs because of placental fusion
during development.

39.  It can be done by grafting genetically
different parents, different cultivates or
different species.
 Tissues get partially fused together

40.  These are chimeras in which the layers
differ in their chromosome constitution.
 Occaionally occurs due to loss or gain of
individual chromosome or chromosomal
fragments owing to miss divsion.
 It has various effects on cell size and
growth characteristics.

41.  These chimerism arise by spontaneous or
induced mutation of a nuclear gene to a
dominant and recessive allele.
 One character is affected at a time in leaf,
flower, fruit and other parts.

42.  These arise by spontaneous or induced
mutation of a plastid gene.
 Plastids may sort-out from a mixed egg or
mixed zygote respectively.
 It affects the colour of the plasmids with in
the leaves.

43.  It is the most lethal virus
till date.
 Developed by soviet
union in 1980 as “Project
Chimera”.
 Virus was developed by
combining DNA of
Venezuelan Equine
Encephalitis Virus,
Smallpox Virus and Ebola
Virus.
 Developed as a bio-
weapon.
 The project was
abandoned due to its
significant risks.