Prenatal Development and Birth

I. From Conception to Birth

The entire zygote is contained within the zona pellucida, a delicate envelope that forms its boundaries.

There are 3 basic periods of prenatal development: &

A. Germinal Period – 8 to 10 days to 2 weeks; ends with egg attachment to uterine wall. Cleavage – the mitotic division of the zygote into several cells; begins at 24 hours after conception. Division rates are different and this yields heterogeneity – variability in the rate of change of different parts.

1. As cleavage occurs, a cluster of cells called the morula take shape in the zona pellucida. After the 5^th day post-conception, the cells begin taking in nutrients; this is the first interaction with the environment (the fallopian tube).

2. A fluid filled cavity forms in the morula thus facilitating the change into a blastocyst – hollow sphere of cells. The blastocyst has two kinds of cells. One set ofsmall cells are the inner cell mass, which gives rise to the organisms, whereas the other set of flat cells surrounding the inner cell mass called the trophoblast, form a protective barrier b/w the inner cell mass and the environment.

3. As the blastocyst moves further into the uterus, the trophoblast cells branch out into the mother’s uterus to the blood vessels. This begins implantation, the process by which the blastocyst becomes attached to the uterus. This action marks the transition to the embryonic period.

B. Embryonic Period – up to 8 weeks; ends when all major organs have formed. The embryo is surrounded by the amnion, a thin, tough, transparent membrane that holds the amniotic fluid, which protects the embryo from damaging movements.

1. Surrounding the amnion is the chorion, the precursor to the placenta, a complex organ of tissue from mom and embryo that acts as a filter allowing oxygen, nutrients, and waste to be exchanged. Waste is filtered through mom’s kidneys and excreted.

2. While the trophoblast is forming the placenta and other membranes, the inner cell mass is busy evolving into organs. Then the inner cell mass separates into two layers:

a. ectoderm – outer; skin, nails, teeth, eye lens, inner ear, and nervous system

b. endoderm – inner; digestive system and lungs

Then a third layer develops b/w these two:

c. mesoderm – middle; muscles, circulatory system & inner skin

3. Organogenesis – process of organ formation that takes place during first two prenatal months.

4. Human growth follows two patterns from now until adolescence:

a. cephalocaudal – head to toe (arms then legs)

b. proximodistal – inside to out (shoulder before wrists)

C. Fetal Period – from 9 weeks to birth (30 weeks); bones harden and infant is able to survive outside mother. At 17 to 18 weeks fetal activity declines as the higher regions of the brain develop. This period of inhibited activity persists until six months. Then activity increases.

1. At this point the fetus experiences endogenous (internal to fetus) and exogenous (external) movement. Movement is essential for limb development.

D. Prenatal Care

Appropriate prenatal care includes the following:

· screening for conditions/disease

· educational literature

· Information on social services

· Information on immunizations and future medical care

· Information on delivery and nursing

E. Sensory Capacities &

1. Motion – the vestibular system controls balance and develops and functions at 5 months. This helps fetus sense changes so it can adjust inutero.

2. Vision – it is thought at 26 weeks (6.5 months) the fetus senses light.

3. Sound – at 4 months the fetus responds to sound; fetuses prefer mother’s voice postnatally because they are use to hearing it while in the womb.

4. Learning – hard to investigate; studies have shown that newborns prefer their mother's heart rate over other heart rates, and when read "Cat in the Hat" prenatally, newborns are calmed/comforted when it is read after birth.

II. Influences on Prenatal Development

A. Miscarriage/Spontaneous Abortion

Pregnancy ends before developing organism is mature enough to survive outside the womb.

Embryo separates from uterine wall and is expelled by the uterus.

15-20% of all pregnancies end in spontaneous abortion, most in first 2-3 months (some before mom had knowledge of pregnancy)

Elected abortions yield risk to mother as well.

B. Maternal Characteristics

1. The mother’s conditions (physical, emotional, psychological) can affect the growing fetus.

2. Evidence shows that mom’s attitude about pregnancy affects child long-term; anxious mothers yield hyperactive and irritable infants

3. Malnutrition – if fetus does not get sufficient nutrients before birth, MR and/or death can occur.

· Not just 3^rd-world countries – poor prenatal care in U.S.

· Mothers concerned about their "weight/figure"

4. Mother's age is a factor. Prime child-bearing age is 22-28. Teenage mothers and women over 40 are more likely to have labor complications.

C. Teratogens – environmental agents that "can" cause deviations in normal development and can lead to abnormalities or death. There are many types of teratogens:

1. Disease – illness and infections can affect the fetus prenatally and perinatally.

a. Rubella – German measles; it’s the fever that causes blindness in infants. We have vaccine.

b. AIDS – 50% of infants born to HIV positive moms acquire the disease; via prenatal barrier or during delivery.

c. Rh incompatibility – Rh complex exists on surface of red blood cells. Mom and baby need to have same, either Rh+ or Rh-. If not, second child will be harmed b/c mom’s body created antibodies to fight off the second child that mom’s body perceives as an antigen (foreign substance). Only when mom is negative and infant is positive.

d. Fever – if mother has high fever, fetus’ core body temperature may get too high thus brain damage occurs; if fetus or infant gets fever, may result in MR or death.

2. Drugs – 60% of all women take some form of drug during pregnancy. Here are 5 types of drugs and their known effects:

a. prescriptions – thalidomide was given for nausea to pregnant women; effects = no limbs, vision & hearing deficits. Aspirin can also cause abnormalities.

b. Tobacco – 26% higher chance of stillborn and death at birth. Infants have lower birthweight and more likely to die of SIDS.

c. Alcohol – heavy drinker = 3 ounces of pure alcohol/day. If so, 71% of these infants were abnormal and/or have fetal alcohol syndrome – small head, underdeveloped brain, congenital heart disease, facial malformations, and joint anomolies.

d. Cocaine – addictive stimulant; infants of cocaine using mothers are irritable, liable to react excessively to stimulation, uncoordinated, and slow learners (crack babies)

e. Methadone/heroin – infants are born addicted to these and must receive it after birth to aid with withdrawal; these infants are premature, underweight, prone to respiratory illness, and have low attention spans.

3. Environment

a. Abuse – any trauma that mom receives (e.g., get kicked in stomach) can damage fetus and result in MR or death.

b. Radiation – high doses = prenatal death, spontaneous abortion, and/or MR

c. Pollution – what mom breathes, fetus receives as well.

III. The Process of Birth

A. Three Stages of Labor:

1. First – from first intense contraction until cervix (opening b/w uterus & vagina) is fully dilated.

2. Second – begins when baby is pushed headfirst into vagina; contractions = 1 minute in duration & 1 minute apart.

3. Third – when baby emerges from vagina & uterus contracts; contractions expel placenta & other membranes

B. Perinatal Hazards (Delivery Complications) &

1. Forceps/suction

2. Oxygen deprivation (anoxia)

3. Long contractions

4. Infection

5. Precipitate delivery – takes place too rapidly; too much force

6. Trauma (breech = butt first; transverse = lateral)

C. Use of Drugs

1. Different drugs have been used: anesthetics, analgesics, and sedatives.

2. Effects on infant may occur b/c drugs pass through placenta barrier, blood brain barrier, and through umbilical cord. Long term effects are not supported empirically (1992).

3. Administration methods:

a. IV

b. IM

c. Epidural (spinal block)

D. Childbirth Strategies

1. Standard – hospital; waiting room; strapped in; become dilated; fully effaced; doctor comes; wheeled to delivery room; have baby; taken and cleaned up; returned; wheeled to recovery/own room.

2. Leboyer Method – French obstetrician:

· no violence to infant

· doctor places infant on mother’s stomach

· uses warm lights and/or bath

· Mom caresses infant before cutting cord

3. Natural or Prepared – based on parent confidence

· usually no drugs involved

· flexible; lots of variance

4. Lamaze Method – French obstetrician; strategies (mainly breathing) to help cope with pain during delivery so to use less or no medication

5. The Doula – Greek word for woman helper; are part of birthing team; like midwives

E. Family Participation – traditional childbirth methods have left family members out of delivery process.

Now, fathers go to regular doctor appointments, attend all prenatal classes, Lamaze classes, are labor "coaches," usually in delivery room.

The same changes are occurring for siblings as well (e.g., doctor visits, hospital tours)

F. Permaturity and Low Birth Weight

These are two very different concepts:

1. Prematurity – when infant is born before 38^th week of gestation. Leading cause of death to preterm babies is immature lungs; second is weak immune system.

2. Low birth weight – when infant weighs 2500 grams (83 oz; 5.5 lbs) or less at birth regardless if it is premature or not. These experience fetal growth retardation for reasons discussed earlier.

G. The Postpartum Period

Birth marks the beginning of the parent-child relationship.

1. Appearance – how the infant is shaped and looks can determine the parents’ response to it.

2. Attachment – primary bond between infant and primary caregiver (usually mom) that is thought to need to take place immediately after birth; it is physical, emotional, and psychological bond.

This is another example of a critical period of development.

3. The postpartum period is the adjustment period after delivery. Varies but on average, lasts 6 weeks, when return to pre-pregnancy state (more like 9 months). Changes occur very quickly.

4. Physical Adjustments:

a. Involution – process by which the uterus returns to its prepregnancy size; 5-6 weeks after birth. Nursing helps to contract the uterus at a fast rate.

b. Sudden and dramatic hormone production changes; if not nursing, will mense 4-8 weeks after birth. If nursing, menses are delayed (but one still can conceive)

c. On average, no sexual intercourse for 6 weeks (for many, it’s a lot longer)

5. Emotional Adjustments:

a. Because of all the changes involved with a newborn, many women experience anxiety, depression, and/or difficulty coping with stress.

b. Postpartum depression affects as many as 70% of women; less often long-term with working moms who return to work

6. Psychological Adjustments:

a. Your time; newborns are extremely demanding

b. Your lifestyle changes; activities revolve around child

c. Budget changes

d. Network of friends may change

Date: 2015-01-29; view: 1226