General facts about pregnancy

1. General facts about pregnancy • Pregnancy lasts for 266 days on average. • Doctors count first day last menstrual period (LMP)—not the day you conceive--as the first day of pregnancy • According to the medical model, pregnancy lasts 40 weeks; it’s actually 38 weeks from the time of conception until birth (on average).

2. Three distinct periods of development • Period of the zygote (weeks 1-2)-also called the germinal period • Period of the embryo (weeks 3-8) • Period of the fetus (weeks 9-38) • **These are not the same as first, second, and third trimester

3. Period of the zygote (germinal period) • First two weeks after conception • Period of rapid development • Zygote becomes the blastocyst--hollow inner layer of cells, which implants into the uterine lining on days 7-9 • Trophoblast—outer layer of cells; becomes the placenta • Differentiation of cells begin • 30-50% of conceptions don’t make it through this period • Placenta is formed at the end of this stage

4. Life support systems of the embryo • Amnion—sac filled with clear fluid in which embryo floats • Placenta—disk-shaped group of tissues that allows food and oxygen to reach the embryo; carries waste products away • Umbilical cord—contains two arteries and one vein that connect the baby to the placenta. • Embryo’s and mom’s blood supplies come in close contact but never mix directly

5. Placenta at around 8 weeks

6. Placenta at birth • The placenta is the baby’s life support system throughout pregnancy.

7. Developmental trends • Cephalocaudal—from head to tail; development occurs head-down • Head region accounts for 50% of total length during the first month • Proximodistal—development occurs “from the inside out”—midline outward • Same pattern of development throughout childhood

8. Period of the embryo • Dramatic and rapid growth takes place • Groundwork for all body structures and internal organs is laid • By the end of this period, all of the structures and internal organs a baby is born with are already formed • By the end of this period, embryo loses its gills and tail and looks more human.

9. Cellular differentiation in the embryo • Three distinct layers are formed: • Ectoderm: outer layer of the embryo—gives rise to the nervous system, skin, hair, teeth, nails, and teeth • Mesoderm: middle layer—gives rise to muscles, skeleton, circulatory, and excretory systems • Endoderm: inner layer which gives rise to the respiratory system, liver, and pancrease

10. Organogenesis during the first four weeks • The process of organ formation • 3rd week: neural tube forms (becomes spinal cord) • 21 days—eyes appear • 24 days—heart cells begin to differentiate • 4th week—urogenital system is apparent; arm & leg buds emerge • Primitive mouth, intestinal tract, liver form • Primitive brain forms • Embryo is 1/6 of an inch long

11. The embryo at 6 weeks

12. Neural Induction • The process of beginning the development of the nervous system at the start of the third week • Starts with a chemical signal from the mesoderm to the ectoderm, causing a portion of the ectoderm to become the neural plate

13. Nervous System Development • Begins with neural induction of the neural plate • Neural tube then forms; top becomes the brain and the rest becomes the spinal cord. • Even in the early days of neural tube development, neurons know to what part of the brain they’ll travel and what time of nerve cell they’ll become (motor, vision, hearing, etc.)

14. Speed of Neural Development • Cell proliferation: nerve cells begin to form in the neural tube at a rate of 250,000 per minute for the entire pregnancy. 30,000 synapses are formed every second. Baby is born with 100 billion neurons. • Cell migration: begins during 7th week; neurons begin their destination in the developing brain. • Some neurons travel distances equal to the distance between Boston and San Francisco! • 1000 trillion connections in the brain begin to form, followed by a pruning process that continues throughout life.

15. Embryonic development at 8 weeks • Embryo is 1 ½ inches long and 1 oz. In weight • Arm and leg differentiate further • Elaborate peripheral nervous system in place • Glandular system operating • Internal sex organs developed (NOTE: Sex is determined at conception.) • Embryo can move, but movements can’t be felt by mom yet. • 95% of body parts are differentiated (arms, legs, beating heart, nervous system, etc.) by the 8th week.

16. 8-week-old embryo

17. Early Period of the fetus (weeks 9-12) • Embryo becomes a fetus when bone replaces cartilage • Facial features become distinct, human-like • Vocal cords, nails, lungs have formed • External genitalia are identifiable • Heartbeat can be heard • Baby can urinate • Baby can smile, frown, suck, and swallow • About 3 inches long; weighs about 1 ounce

18. Middle months of period of the fetus (5th-6th month) • 12-15 inches long, 12-32 ounces • Grasping reflex; baby sucks thumb • Lung breathing is possible • Sleep/wake cycles similar to newborn’s • Eyes and ears are sensitive to light and sound; visibility is obtained. • Very sensitive to touch • All neurons present by 24 weeks’ gestation • Rapid growth during 6th month; slows during 7th month.

19. Vernix and lanugo • Appear in 5th-6th month • Vernix—cheeselike covering to protect skin from chapping • Lanugo—white, downy hair on body to protect skin from chapping

20. Fetus with vernix and lanugo • Vernix and lanugo are often still present at birth, especially if the baby is preterm.

21. Age of viability • This is the age by which the fetus can survive outside the womb • Usually this is between 22-26 weeks’ gestation • By the 24th week, the fetus has a 50% chance of survival.

22. Fetal Development by Month • 3rd month: sex organs appear. Visible by 12 weeks. • 4th month: rapid growth; red blood cells develop; active sucking reflex • 5th month: hears sound, sleeps, 10-12 oz. long, 1 pound • 6th month: rapid growth, 12-14 inches, 2 pounds • 7th month: growth slows; viability attained • 8th and 9th month: baby plumps up, senses ready to function, brain is 25% of adult weight

23. Last months (7-9) of pregnancy • Lungs gradually mature • Rapid brain development causes sensory & behavioral capacities to expand • Antibodies are transferred from mom to baby • Baby becomes better able to regulate temperature • Gains 3.5 pounds in fat • Engagement (baby’s head in birth canal) by 36 weeks • Baby weighs on average 7 ½ pounds at birth

24. Ethical Issues during Pregnancy • Embryonic adoption…what to do with frozen embryos that the biological parents do not want • Stem cell research • Embryonic stem cells are those cells that have been removed from the inner cell mass of the blastocyst about 4 days after conception. • These cells are called pluripotent cells, which are capable of becoming almost any cell in the human body until they begin to specialize. If left alone, the pluripotent cells develop into a viable embryo.

25. Sex Differences in Utero • Males are more physically active—they remain more active through childhood • Females are more sensitive to external stimulation • Females advance more rapidly in skeletal development and are 1-2 weeks ahead of males in bone development at birth. Trait remains through early adolescence. • More boys are conceived than girls, but the birth rate is roughly equal (105 males to 100 females)

26. Mozart effect • The finding that exposing fetuses and babies to classical music (specifically Mozart) is associated with greater math and spatial ability test scores. • The finding has been disputed recently. Seems to increase math skills in adults for about 30 minutes after listening to it.

27. Sounds and tastes infants prefer • They prefer their mother’s voice over all others • No preference in father’s voice over other men’s • Fetuses develop taste preferences and aversions; strong tastes such as garlic are present in the amniotic fluid (also in breast milk) • Fetal tastes may influence later taste preferences.

28. Habituation • Getting accustomed to a certain stimulus in the womb • Fetuses at 26 weeks of age show habituation to repeated stimuli • Some psychologists think that how quickly a fetus habituates to a routine stimulus predicts future intelligence. This is debatable.

29. Teratogens • Any environmental agent that can interfere with the process of normal growth (even vitamins can be teratogens) • Especially harmful in the embryonic stage because this is when organs are being formed. • Effects of a teratogenic substance are worse on the body part or organ systems that are being formed at the time of exposure

30. Does a teratogen always cause damage? • No—a specific teratogen usually does NOT cause a specific birth defect. • Three factors influence the effects of a teratogen: • Dose—the greater the dose, the greater the effect. • Genetic susceptibility—both the mother’s and baby’s genotypes influence vulnerability. • Timing—Teratogens do more damage at specific times of development.

31. Times of greatest vulnerability when exposed to teratogens Brain: 15 to 25 days after conception Eyes: 24-40 days after conception Heart: 20 to 40 days after conception Legs: 24-37 days *Each body part has its own critical time of formation. Only about half of all potential effects of a teratogen are evident at birth.

32. Why are teratogens harmful to baby but not to Mom? • Mother weighs a lot more • Mother’s organs aren’t developing like the baby’s are • The placenta and immature fetal liver may be unable to convert a harmful substance to a harmless one

33. STORCH • Refers to the following infectious diseases that are teratogens • Syphilis (50% die; blindness, retardation, deafness) • Toxoplasmosis (protozoan virus transmitted by cats; neurological problems, preterm delivery, or miscarriage) • Other infections (flu, chicken pox, measles, etc.) • Rubella (German measles; blindness, deafness, retardation, death) • Cytomegalovirus (CMV..no treatment for this…casus retardation, blindness, deafness, possibly death) • Herpes (Herpes II is the genital kind; contracted in birth canal; child develops symptoms in 1st week of life. Affects CNS.)

34. Examples of teratogens • Over-the-counter, prescription, and illegal drugs • Caffeine—medical opinions differ as to whether it’s harmful or not (4 cups or more of coffee a day is considered harmful) • Tobacco—associated with low birth weight, miscarriage, SIDS, asthma, and childhood cancer • Alcohol—can result in fetal alcohol syndrome • Maternal malnutrition—smaller brain size • Maternal stress—associated with miscarriage, preterm labor, low birth weight

35. Fetal alcohol syndrome • Involves mental retardation, impaired motor coordination, poor attention and memory, and certain physical characteristics.

36. Heroin • Well-documented effects: behavioral disturbances in children of heroin-addicted mothers • Infants have tremors, show irritability, abnormal crying, sleep disturbances, and impaired motor control. • These are all symptoms of heroin withdrawal. • Many still have behavioral problems at 1 year old, and studies show attention deficits later in development.

37. Methamphetamine (meth) • Babies are at significant risk of infant mortality, low birth weight, and developmental and behavioral problems. • Respiratory difficulties, neurological problems, poor cognitive functioning, and abuse and neglect by parents are common. • Meth use during pregnancy is increasing and is now considered an even greater problem than cocaine use.

38. What about fish? • Some fish, especially large fish such as tuna, sharks, swordfish, etc., contain high levels of mercury. • Mercury crosses the placenta easily and leaves the infant highly sensitive to brain and nervous system defects. • FDA in 2004 advised women of childbearing age and young children not to eat shark, swordfish, king mackerel or tilefish. They can eat up to 12 ounces (2 meals) a week of shrimp, canned light tuna, salmon, pollock, & catfish.

39. Maternal Age • Considered a teratogen • Over age 35, problems increase dramatically (more trouble getting pregnant, risk of birth defects & chromosomal problems) • Teenage mothers show the same problems as older mothers, especially in rates of Down’s syndrome

40. What about paternal age? • Older fathers have children who face increased risk of certain birth defects, including Down syndrome, dwarfism, Marfan syndrome (involves head & limb deformities), and perhaps autism. • When both parents are older (mom over 35; dad over 40), the risk of miscarriage is greater.

41. Genital herpes • Newborns contract genital herpes when they pass through the birth canal of an infected mother. • About 1/3 of the babies die, and another ¼ are brain damaged if delivered by a mother with active herpes. • A C-section may be performed if mother has an active case of herpes near the time of delivery.

42. AIDS • Mothers can transmit HIV to their infants in one of 3 ways: • Across the placenta • During delivery through contact with maternal blood/fluids • Postpartum through breastfeeding • Infants can be infected but asymptomatic; they can still develop symptoms up to 15 months old. Risk is reduced by giving pregnant HIV-infected moms AZT during pregnancy and the baby AZT after birth; a “bloodless” C-section can also help. An infected mother will pass HIV along 30-50% of the time

43. AIDS in babies • AIDS embryopathy may develop when the virus is transmitted. • Results in growth retardation, microcephaly, flat nose, widespread, upward-slanted eyes. • Associated with higher rates of preterm disease, low birth weight, and miscarriage. • AIDS has slower incubation period in fetuses than adults. Symptoms often appear as early as 6 months (weight loss, diarrhea, fever, chronic infections). • Babies rarely survive more than 5-8 months once symptoms appear.

44. AIDS embryopathy

45. The Rh problem • If a woman has Rh - blood and the father has Rh +, the fetus may be born with Rh + blood. • Antibodies in the mother may attack the fetus as being “foreign.” • Can result in miscarriage, stillbirth, anemia, jaundice, heart defects, brain damage, or death soon after birth. • First Rh-positive baby is usually not affected; subsequent babies are. • Moms are given a RhoGam vaccine within 3 days of delivery to prevent antibodies from being produced.

46. Prematurity • Babies born 3 weeks or more before the end of pregnancy OR who weigh less than 5.5 pounds • Birth weight is best predictor of infant survival and healthy development • Best scenario is to be at least 2 pounds at birth and 32 weeks’ gestation • Preterm babies are more difficult infants than other babies are and have a greater risk for abuse.

47. Causes of Prematurity • Low socioeconomic status: 1 in 4 babies are born in underdeveloped countries • Infections • Smoking and drinking • Mom’s age (under 17 or over 35)—high correlation • Cervical problems, high blood pressure, unusual stress, diabetes, heart diseases • Often impossible to determine

48. Prematurity Stereotyping • The tendency for people to view premature babies as weaker, more vulnerable, and less competent than full-term babies, even after the premature babies have caught up developmentally with full-term peers • Developmental milestones may, in fact, be reached a little more slowly in preterm babies. • Experiment showed that people judged a 9-month-old healthy looking baby as “weaker, less sociable, and less cognitively competent” if told the baby had been premature.

49. Micro-preemie (at the very edge of viability) This infant was born at 23 weeks and weighed 1 lb. 2.6 oz.

50. The same preemie at 4 years • Although asthmatic and slightly developmentally delayed, she’s doing great!