Conception and Prenatal Development: From Conception to Birth

1. CHAPTER THREE PRENATAL DEVELOPMENT AND BIRTH

2. I. CONCEPTION The first step in the development of an individual human being happens at conception, when each of us receives a combination of genes that will shape our experiences throughout the rest of our lives

3. A. The Process of Conception Conception occurs when a sperm penetrates an ovum Most cells in the human body contain 23 pairs of chromosomes Gametes are cells that have only 23 chromosomes At conception, the 23 chromosomes of the sperm unite with the 23 chromosomes of the ovum so that the fertilized egg has 23 pairs of chromosomes in an entirely new cell called a zygote Chromosomes are composed of molecules of a chemical called deoxyribonucleic acid (DNA) that is further subdivided into segments called genes (continued)

4. The Process of Conception (continued) Fraternal twins, also called dizygotic twins, are conceived when two eggs are fertilized by two separate sperm Identical twins, also called monozygotic twins, are conceived when a single fertilized ovum separates into two parts, and each develops into a separate individual The annual number of multiple births has tripled in Canada since the late 1980s; births of triplets, quadruplets, and quintuplets have increased by over 230% since the mid-1990s (continued)

5. The Process of Conception (continued) Assisted Human Reproduction (AHR) New Canadian legislation protects the health and safety of those undergoing AHR and the children born from such procedures Fertility drugs are one of the many assisted human reproductive (AHR) techniques available to couples who have trouble conceiving Cryopreservation freezes the multiple embryos created in IVF (In vitro fertilization) labs, using vitrification protocols to speed the cooling Artificial Insemination injects sperm directly into a woman’s uterus

6. II. PREGNANCY & PRENATAL DEVELOPMENT Pregnancy is a physical condition in which a woman’s body is nurturing a developing embryo or fetus Prenatal development, or gestation, is the process that transforms a zygote into a newborn

7. A. The Mother’s Experience First Trimester Pregnancy begins when the zygote implants itself in the lining of the woman’s uterus Morning sickness: feelings of nausea Prenatal care is essential in the first trimester to prevent birth defects because all of the baby’s organs form during the first eight weeks Early prenatal care can also be important to the woman’s own health (continued)

8. The Mother’s Experience (continued) Second Trimester The woman gains weight and the uterus expands The woman begins to feel the fetus’s movements Prenatal visits include monitoring the mother’s and the baby’s vital functions and keeping track of the womb’s growth (continued)

9. The Mother’s Experience (continued) Third Trimester At 25 weeks, the pregnant woman enters her third trimester Weight gain and abdominal enlargement Women begin to feel more emotionally connected to the fetus Toxemia of pregnancy (a life-threatening condition) may occur — signalled by a sudden increase in blood pressure

10. Pregnancy Summary

11. B. Prenatal Development Cephalocaudal pattern—growth that proceeds from the head downward Proximodistal pattern—growth that proceeds from the middle of the body outward (continued)

12. Prenatal Development (continued) The first two weeks of gestation, from conception to implantation, constitute the germinal stage Placenta: specialized organ that allows substances to be transferred from mother to embryo and from embryo to mother, without their blood mixing Umbilical cord: organ that connects the embryo to the placenta Amnion: fluid-filled sac in which the fetus floats until just before it is born (continued)

13. Prenatal Development (continued) The embryonic stage begins when implantation is complete, at about the end of the second week of pregnancy Neurons: specialized cells of the nervous system Gonads: sex glands (ovaries in females; testes in males) Organogenesis: process of organ development (continued)

14. Structure of a Single Developed Neuron

15. Prenatal Development (continued) The final stage is the fetal stage, beginning at the end of week eight and continuing until birth, about seven months This stage involves refinements of the organ systems, especially the lungs and brain, that are essential to life outside the womb Viability: ability of the fetus to survive outside the womb (continued)

16. Prenatal Development (continued) Most of the formation and fine-tuning of the brain takes place during the fetal stage Neuronal proliferation is the faster pace of neural formation between the 10th and 18th weeks Between the 13th and 21st weeks, newly formed neurons consisting only of cell bodies migrate to the parts of the brain where they will reside for the rest of one’s life Synapses, axons and dendrites subsequently develop Glial cells: specialized cells in the brain that support neurons

17. C. Sex Differences Male fetuses are more physically active than female fetuses The male embryo secretes the male hormone testosterone Male fetuses secrete small amounts of testosterone into the amniotic fluid Subtle sex differences in prenatal brain development probably contribute to different patterns of growth-hormone secretions in adolescence Female fetuses appear to be more sensitive to external stimulation and advance more rapidly in skeletal development Males are more vulnerable to all kinds of prenatal problems Males are more likely to be spontaneously aborted Males are more likely to have birth defects

18. D. Prenatal Behaviour As early as the 25th week, fetuses respond to sounds and vibrations with heart rate changes, head turns, and body movements By the 32nd or 33rd week, fetuses can distinguish between familiar and novel stimuli Newborns appear to remember stimuli to which they were exposed prenatally—their mother’s heartbeats, the odour of the amniotic fluid, and stories or pieces of music they heard in the womb Stable individual differences in behaviour: Very active fetuses tend to become children who are very active and are more likely to be labelled “hyperactive” by parents and teachers Fetuses who are less active than average are more likely to be intellectually delayed

19. III. ISSUES IN PRENATAL DEVELOPMENT Congenital anomaly: an abnormality present at birth Prenatal development is not immune to outside influences Most of the problems are very rare, many are preventable, and many need not have permanent consequences for the child

20. A. Genetic Disorders

21. B. Chromosomal Errors A trisomy is a condition in which a child has three copies of a specific autosome The most common is trisomy 21, or Down syndrome, in which the child has three copies of chromosome 21 The risk of bearing a child with trisomy 21 rises with maternal age Anomalies associated with the sex chromosomes: Klinefelter’s syndrome Turner’s syndrome Boys with an extra Y chromosome (XYY) are taller than average and have large teeth

22. C. Teratogens: Maternal Diseases Deviations in prenatal development can result from exposure to teratogens, agents that cause damage to an embryo or fetus The greatest risk from most teratogens is in the first eight weeks of gestation, because most organ systems develop most rapidly during this period

23. Sensitivity to Teratogens throughout the Prenatal Period

24. Some Important Teratogens and their Effects

25. D.Teratogens: Drugs Any drug can be teratogenic The Thalidomide tragedy of the 1960s Relatively common drugs used in the treatment of anxiety and depression can have teratogic effects (e.g benzodiazepines, SSRIs) Doctors advise against taking any unnecessary medicines during pregnancy (continued)

26. Teratogens: Drugs (continued) Tobacco Low birth weight contributes to increased rate of miscarriage, stillbirth and neonatal death Alcohol An ovum or a zygote can be affected before implantation in the uterus Heavy alcohol intake may result in a child with fetal alcohol syndrome Psychotropic Drugs Use results in a wide range of effects, from an addicted child to miscarriage

27. E. Teratogens: Other Harmful Influences on PrenatalDevelopment Diet Body Mass Index (BMI) is a ratio of weight to height that estimates healthy and unhealthy body composition Age Chronic illness Maternal emotions

28. F. Teratogens: Mutagenic, Environmental and Epimutagenic Mutagens cause changes (mutations) in genomic DNA Environmental teratogens damage cells or disrupt normal cell development Epimutagenic teratogens cause abnormal gene silencing or expression

29. G. Paternal Influences: Preconceptual and Prenatal There is high reproductive risk in many professions that expose a potential father to teratogens Contamination of the mother and fetus can occur through seminal fluids or by toxins being brought into the home Adverse birth outcomes and congenital anomalies in offspring have been linked with both teen fathers and older fathers Physical abuse of the mother during pregnancy can result in injury to the fetus

30. H. Fetal Assessment and Treatment Preconception and first trimester procedures can screen women at risk of bearing a child with a congenital defect. Tests include: Chorionic villus sampling (CVS) Amniocentesis Alpha-fetoprotein sampling Fetoscopy

31. Chorionic villus sampling (CVS) and Amniocentesis

32. IV. BIRTH AND THE NEONATE Once gestation is complete, the fetus must be born - an event that holds some pain as well as a good deal of joy for most parents

33. A. Birth Choices Midwives are regulated health professionals in most Provinces and Territories in Canada There are three types of drugs commonly used during labour and delivery Analgesics Sedatives or tranquilizers Anaesthesia The following are the four alternatives typically available in Canada for where the baby can be born: A traditional hospital maternity unit A hospital-based birth centre or birthing room A free-standing birth centre Home delivery

34. B. The Physical Process of Birth Stage 1 includes two important processes: Dilation is the opening of the cervix so it is large enough (about 10 cm) for the baby to pass through Effacement is the flattening of the cervix When the cervix is dilated, the second stage of labour occurs—the actual delivery of the baby Stage three, called the afterbirth, is the delivery of the placenta and other material from the uterus Most infants are delivered head first, facing toward the mother’s spine A breech birth occurs when the baby is oriented differently, either feet first or bottom first (continued)

35. The Sequence of Steps During Delivery

36. Typical Pattern of the Stages for First Births and Subsequent Births

37. The Physical Process of Birth (continued) During the process of birth, some babies go into fetal distress, a sudden change in the baby’s heart rate Anoxia, or oxygen deprivation, can result in death or brain damage After birth, most women require a period of a month or so to recover

38. C. Assessing the Neonate Neonate: term for babies between birth and 1 month of age The health of neonates is usually assessed using the Apgar scale Standard screening is done for rare metabolic disorders The Brazelton Neonatal Behavioural Assessment Scale tracks a newborn’s development over about the first 2 weeks after birth to identify significant neurological disorders The Nipissing District Developmental Screen can be used with children from 1 month to 6 years of age to screen for a variety of developmental problems

39. The Apgar Scale

40. D. Low Birth Weight Low birth weight (LBW): newborn weight below 2500 grams Most LBW infants are preterm, or born before the 38th week of gestation Some infants are full-term but still weigh less than 2500 grams and are called small-for-date Those below 1500 grams have significantly higher rates of long-term problems, lower intelligence test scores, smaller size, and more problems in school