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7. 9th week to birth embryology
The document summarizes key aspects of prenatal development from conception through birth. It describes the major periods (germinal, embryonic, fetal), key developmental milestones in each, and factors that can impact development like teratogens and medical interventions. It outlines risks like low birthweight and anoxia, the assessment of newborns using the Apgar scale, and importance of social support through parenting and bonding in early life.
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7. 9th week to birth embryology
- 1. Sex Chromosomes • • • • • • XX =Female XY = Male XO = Female, Turner’s Syndrome XXY = Male, Kleinfelter’s Syndrome XYY = Male, Double Y Syndrome Fragile X = Male or Female Berch & Bender (1987); Berger, K. S. (2006); Doyle & Paludi (1998). 1
- 2. Part I Chapter Four PrenatalDevelopment and Birth From Zygote to Newborn Risk Reduction Birth 2
- 3. From Zygote toNewborn • Prenatal development is divided into three main periods: – Germinal period (0-2 weeks) – Embryonic period (3-8 weeks) – Fetal period (9 weeks-birth) 3
- 4. Timing • Pregnancy beginsat conception – Start of gestational age – Obstetrician may use LMP – 14 days before conception • Length of pregnancy – 266 days, 38 weeks, or 9 months – LMP = 40 weeks 4
- 5. Timing • Trimesters (3mo.) vs. germinal, embryonic, and fetal periods • Due date – Based on LMP – 5% babies born on that date – Full term = 3 weeks early or 2 weeks late (preterm and post-term) 5
- 6. Germinal: The First14 Days • Germinal period: – First two weeks of prenatal development after conception – Characterized by rapid cell division and the beginning of cell differentiation 6
- 7. • Embryonic period: –Approximately the third through eighth week after conception • all body structures, including internal organs, begin to develop • Fetal period: – Stage of prenatal development from ninth week after conception until birth, during which the organs grow in size and mature in functioning 7
- 8. Germinal: The First14 Days • Implantation: – process in which developing organism burrows into placenta that lines uterus • Placenta: – organ that surrounds developing embryo and fetus, sustaining life via the umbilical cord 8
- 9. Embryo: From theThird Through the Eighth Week • Embryo: a developing human organism from about the third through the eighth week after conception 4 weeks ¼ in. 5 weeks 7 wks. <1 in. 8 wks. 1 in. 9
- 10. Fetus: From theNinth Week Until Birth • The developing organism is called a fetus from the start of the ninth week after conception until birth 10
- 11. The Third Month •At the end of the third month, the fetus has all its body parts • Weighs approximately 3 ounces and is about 3 inches long 11
- 12. • In thefourth, fifth and sixth months: – Heartbeat becomes stronger – Cardiovascular system becomes more active – Brain increases about six times in size 12
- 13. • Age ofviability: age at which a fetus can survive outside the mother’s uterus if specialized medical care is available – About 22 weeks after conception 13
- 14. Final 3 Months •Brain waves indicate responsiveness • Lungs expand and contract, using the amniotic fluid as a substitute for air • Heart valves, arteries, and veins circulate the fetal blood 14
- 15.
- 16. Risk Reduction • Teratogens:agents and conditions that can – Harm the prenatal brain – Impair the future child’s intellectual and emotional functioning 16
- 17. Determining Risk • Onceit was thought the placenta screened out all harmful substances. 17
- 18. – Teratology: scienceof risk analysis, the study of birth defects – Risk analysis: to determine likelihood of harm, science of weighing the potential effects of a particular: – event – substance – experience 18
- 19.
- 20. – Threshold effect:situation in which a certain teratogen is relatively harmless in small doses but harmful once exposure reaches certain level (the threshold) • Vitamin A beneficial in low doses, dangerous in high doses – Interaction effect: result of a combination of teratogens • Alcohol, tobacco, and marijuana 20
- 21. Genetic Vulnerability – Dizygotictwins, exposed to same teratogens but have only half their genes in common, are born with different abnormalities • Suggests both protective and vulnerable genes – Cleft lip, cleft palate, club foot more common in some families • Suggests genetic vulnerability – Neural tube defects 21
- 22. Protective Measures • Impactof teratogens cannot be predicted before mid-pregnancy • Some pregnant women are exposed to the tetragons with no evident harm • Some defects occur even though the woman avoids all known tetragons while pregnant 22
- 23. A View FromScience • Alcohol in high doses is a proven teratogen • 40 years ago drinking during pregnancy was believed to be harmless • Obstetricians noted that some patients who drank heavily while they were pregnant had babies with distorted faces 23
- 24. • Fetal alcoholsyndrome (FAS) : cluster of birth defects – – – – Abnormal facial characteristics Slow physical growth Cognitive delays or deficits Impulsiveness • Fetal alcohol effects (FAE) : condition in which child has been exposed to alcohol before birth – Some signs of fetal alcohol syndrome but does not meet all the criteria 24
- 25. Benefits of PrenatalCare • Tests done during pregnancy can diagnose problems early on, and remedies can be put in place in some instances • Sonogram: image of unborn fetus (or an internal organ) produced by high-frequency sound waves (ultrasound) 25
- 26. • For full-termfetus and a healthy mother, birth can be simple and quick 26
- 27. The Newborn’s FirstMinutes • Most newborns begin to breathe as soon as their head emerges. – first breath causes infant’s color to change – eyes open wide – the tiny fingers grab – toes stretch and retract – mucus in the baby’s throat is removed – umbilical cord is cut to detach the placenta – placenta is expelled 27
- 28. Apgar scale: quickassessment of newborn’s condition including: – – – – – the baby’s color heart rate reflexes muscle tone respiratory effort 28
- 29. Medical Intervention • About31% of births in the U.S. are cesarean section, (also called c-section) 29
- 30. Birth In DevelopingNations • • • In the U.S. only 1% of births take place at home. Worldwide most births occur at home Doula- a woman who helps with the birth process - Also helps with breastfeeding and newborn care 30
- 31. Anoxia • Anoxia: – lackof oxygen that can cause brain damage or death to the baby – means “no oxygen” • Cerebral palsy: – disorder that results from damage to brain’s motor centers – People with cerebral palsy have difficulty with muscle control, so their speech and body movements are impaired. 31
- 32. Low Birthweight (LBW) •Average weight of a newborn is 7½ lbs. – Low birthweight (LBW): a body weight at birth of less than 5½ lbs. – Very low birthweight (VLBW): a body weight at birth of less than 3 lbs, 5oz. – Extremely low birthweight (ELBW): a body weight at birth of less than 2 lbs, 3 oz. 32
- 33. • Preterm birth:occurs 3 or more weeks before full 38 weeks of a typical pregnancy – Preterm babies are typically (but not always) LBW because they miss final weeks of weight gain – Small for dates or small for gestational age (SGA)- birth weight is lower than expected given the time of conception 33
- 34. Social Support • Thedeveloping person is affected by quality of: – – – – medical care education culture social support • Fathers and other relatives, neighbors, cultures, and, clinics can reduce risk of birth complications 34
- 35. Mothers, Fathers, anda Good Start • Birth complications can have a lingering impact on the new family, depending partly on: – sensitivity of hospital care – the home • To reduce stress on an infant who has to stay in the hospital, parents are encouraged to help with early caregiving. 35
- 36. • Kangaroo care:form of child care in which the mother of a low-birthweight infant spends at least an hour a day holding the baby between her breast, like a kangaroo 36
- 37. Help from Fathers •Fathers can be crucial in the effort to produce a healthy baby. • Supportive father-to-be helps a mother-to-be: – stay healthy – well nourished – drug-free 37
- 38. • Parental alliance:cooperation between a mother and a father based on mutual commitment to their children • Parents agree to support each other in their shared parental roles 38
- 39. Postpartum Depression • Newmother’s feelings of inadequacy and sadness in days and weeks after giving birth including: – irritability – eating disruptions – sadness – feeling overwhelmed and inadequate • Affects 10-15% of women 39
- 40. Bonding • Parent-infant bond:strong, loving connection that forms as parents hold, examine, and feed newborn 40
Editor's Notes
- #2 One X is essential to life. Turner’s syndrome: female, short and immature in appearance, webbed necks, eyelid folds, receding chcins, broad chest. Sterile (missing the X that directs development of ovaries); interest in “feminine” activities. Estrogen therapy to develops secondary sex characteristics. Intellectually fine, even above average. Kleinfelter’s: 1-2/1000 males; average height, long limbs, high pitched voice, sterile, sometimes cognitively imparierd. High prison population – minor crimes, more frequent arrests, not predisposition to criminal activity. YY: 1/1000 males; even taller than males with Kleinfelter’s Syndrome, also have a high crime rate – nonviiolent (theft and larceny); intellectual impairment. Fragile X: 1/3 females cog. Impair; 20% males normal, 33% impaired, rest severely impaired. Fragile-X syndrome is the most common cause of inherited mental impairment. It affects about one in 5000 boys and about one in 2500 girls. As well as learning difficulties, people with Fragile-X may have other symptoms, including anxiety and hyperactivity. Boys are usually more severely affected than girls. Diagnosis of Fragile-X syndrome is important, as special education and therapy can help affected children.
- #5 LMP – date of last menstrual period
- #7 Not yet nourished by the mother so does not increase in size for 10 days. At 10 days, implantation in the uterus occurs. 60% of natural and 70% of in vitro conceptions FAIL to implant.
- #9 Structural information
- #10 About 20% of all embryos are aborted spontaneously , most often because of chromosomal abnormalities. We begin to see the primitive streak, which will become the neural tube 22 days after conception. The neural tube becomes the central nervous system (brain and spinal cord). At 5 weeks we begin to see buds of arms and legs. At 52 and 54 days after conception the fingers and toes separate. At the 7th week, the embryo has eyes, nose and digestive system and the beginning of toes. At the 8th week, the embryo weighs about 1/13 ounce, 1 in. long. All the basic organs and body parts. At this point, the embryo has an indifferent gonad.
- #11 During the fetal period the fetus develops from tiny, sexless creature to a 7 1/2-pound, 20-inch boy or girl. If the embryo is male, in the third month a gene on the Y chromosome commands the development of male sex organs. Female organs are the default mode of no command is given. By week 12, the genitals are fully formed and send hormones to the developing brain. At the end of three months, the fetus has all his or her parts and is about 3 inches long. Individual weight varies consierably, but 3 mo, 3 oz., 3 inches is an easy way to remember approximate measurements at this stage.
- #12 Early prenatal growth is very rapid, but there is considerable variation from fetus to fetus, especially in body weight.
- #14 Advance in brain development – neuron organization, axon development – are critical to attainment of the age of viability. The brain regulates breathing and sucking, which are life-sustaining. < 1 pound, often don’t survive because outside of the womb brain development doesn’t proceed appropriately.Before 22 weeks of gestation a baby will not survive. 50 years ago, it was 23-26 weeks, now 2/3 survive at those ages. Weight is a good indicator of maturity – at 28 weeks, a typical fetus weighs 3 pounds and has a 95% chance of survival. For genetically small babies or multiples, time since conception is the critical variable. The baby pictured here was born after 26 weeks and 6 days, weighed 8.6 oz. She was a twin and weighed 15 pounds by her first birthday.
- #15 Each day in the final three months increased the odds the baby will be healthy, not just survive. Mature neurological, respiratory and cardiac systems are the key. Weight in the last 3 months is about 4.5 pounds. The mother child bond deepens – the baby’s movements increase the mother’s awareness. The baby hears, smells and notices mom’s behavior, being soothed by regular walking and jumping to sudden noises.
- #18 Doctors on an Australian military base traced an increase in blindness among newborns to rubella (German measles) contracted by pregnant women a few months earlier. Realized that some diseases during pregnancy could harm a fetus.
- #19 The effort to understand what triggered such damage gave rise to:
- #20 Thalidomide, a sedative, in the 1950’s had an impact during weeks 6 or 7 when arms and legs are formed, but no impact after week 9.. Timing determines what areas and how profound of an impact a teratogen has on the developing person. Remember, these are called critical periods. Because the exact timing of conception isn’t always know, drs recommend stopping the use of recreational drugs, certain prescription and update their immunizations if they are trying to conceive or are not taking measures to prevent pregnancy. Prenatal vitamins are a part of this preparation. Folic acid is especially important for neural tube formation – which becomes the nervous system. Most people are deficient in folic acid even though many foods are now supplemented with it.