Chapter 4: Prenatal Development and Birth

PSY 2410 107

Length of Pregnancy

40 weeks, 9 months.

Germinal Period

(First 2 weeks after conception): Rapid cell division and beginning of cell differentiation.

Embryonic Period

(Third through eighth week): Basic forms of all body structures develop.

Fetal Period

(Ninth week until birth): Fetus grows in size and matures in functioning.

Germinal Period: First 14 Days

• Zygote begins duplication and division within hours of conception.

• Development of the placenta

• Implantation (about 10 days after conception)

• Implantation fails when a zygote doesn’t develop as it should.

Embryonic Period

a. At 4 weeks past conception, the embryo is only about 1/8 inch (3 millimeters) long, but already the head has taken shape.

b. By 7 weeks, the organism is less than an inch (2 centimeters) long. Eyes, nose, the digestive system, and even the first stage of toe formation can be seen.

Embryo: Weeks 3 Through 8

• Primitive streak (22 days after conception) becomes the neural tube and later forms the brain and spine of the central nervous system.

• Head takes shape.

• Eyes, ears, nose, and mouth form.

• Heart begins to pulsate.

• Extremities develop, and webbed fingers and toes separate.

• Cephalocaudal and proximodistal growth is evident.

• Both male (via Wolffian ducts) and female (via Müllerian ducts) potential in a tiny intersex gonad are present.

Fetal Period

Week 9 until birth

• The third month: Rapid fetus growth with considerable variation

• Average: 3 months; 3 ounces; 3 inches

• Hormones guide growth of the body and brain.

• Third month: Neurological sex differences begin; overlap is common.

Fetus: Middle Three Months

• Large body movements and vigorous leg kicks occur.

• Digestive and excretory systems develop.

• Heartbeat speeds up when the fetus is awake and moving.

• Fingernails, toenails, and buds for teeth form, and hair grows

• Brain maturation allows the fetus to reach the age of viability.

Fetus: Final Three Months

• Neurological, respiratory, and cardiovascular systems develop.

• Lungs expand and contract, and breathing muscles strengthen as the fetus swallows and spits out amniotic fluid.

• Heart valves go through a final maturation.

• Testicles of the male fetus descend.

• Hearing adjusts to sounds.

• The cortex becomes wrinkled, and fontanels develop.

Vulnerability during the Germinal Period (Prenatal Development)

An estimated 65 percent of all zygotes do not grow, or implant properly and thus do not survive the germinal period.

Vulnerability during the Embryonic Period (Prenatal Development)

About 20 percent of all embryos are aborted spontaneously. This is usually called an early miscarriage, a term that implies something wrong with the pregnant person when in fact the most common reason for a spontaneous abortion is a chromosomal malformation.

Vulnerability during the Fetal Period (Prenatal Development)

About 5 percent of all fetuses are aborted spontaneously before viability at 22 weeks or are stillborn, defined as born dead after 22 weeks. This is much more common in low-income nations.

Vulnerability during Birth (Prenatal Development)

Because of all these factors, only about 27 percent of all zygotes grow and survive to become living newborn babies.

By third week after conception:

Specialize neural progenitor cells eventually become brain cells (Neurons); migrate to a particular brain region and specialize.

By mid-pregnancy:

• Billions of neurons create ridges and depression (gyri and sulci), allowing for a larger and more complex brain.

• Cortex layers are produced; back of neck, midbrain, and forebrain develop and connect.

• Synchronized connections between brain parts begin.

Prenatal Growth of the Brain

Birth

• Fetal brain signals the release of hormones to trigger the uterine muscles.

• Average duration for firstborn babies: 12 hours

• Quicker labor for subsequent babies: 7 hours

• Birthing positions vary: Sitting, squatting, lying down, and water births — Cultural and personal preference.

• Prolonged anoxia (lack of oxygen of the mother) can cause brain damage or death.

Newborns

• Usually cry spontaneously

• Color changes from bluish to reddish

• Eyes open, fingers grab, and toes stretch

Apgar Scale

• Quick assessment of newborn’s heart rate, breathing, muscle tone, color, and reflexes

• Completed twice (1 minute and 5 minutes after birth)

• Score of 0, 1, or 2 in each category

• Desired score: 7 or above

• Ratings of birth attendants influenced by culture

Cesarian Sections

• The fetus is removed through incision in the abdomen.

• Medically indicated for about 10–15 percent of births; various conditions suggest surgery; worldwide differences in rate.

• Surgery adds risk for maternal death.

• Only Physicians can perform cesarean sections.

Advantages for C-Sections

• For hospitals: Easier to schedule, quicker, and more expensive than vaginal deliveries.

• For birthing parents: Advance planning, quick birth; VBAC.

• For baby: Beneficial microbiome from birth canal.

Disadvantages for C-Sections

• Breast-feeding is less common, and medical complications are more likely.

• Babies born via c-section are more likely to develop asthma, diabetes, and obesity.

Teratogens

Any agent or condition, including drugs, viruses, pollutants, malnutrition, stress, and more, resulting in congenital disabilities or complication.

Threshold Effect

• Certain teratogens are relatively harmless until exposure reaches a

certain level.

• Thresholds are controversial.

EX: Alcohol consumption. Embryo exposed to heavy drinking can develop fetal alcohol syndrome (FAS).

Genetic Vulnerability

Genes of both the carrier and the fetus interact with teratogens.

Examples of Genetic Susceptibility

• Male fetuses are more often spontaneously aborted, stillborn, or harmed than are female fetuses.

• One maternal allele reduces folic acid that can produce neural-tube defects (spina bifida or anencephaly); more common in certain ethnic groups (e.g., Irish, English, and Egyptian).

Drugs and Pesticides

Unrelated and potentially harmful substances

• Some herbal products

• Over-the-counter drugs

Common Substances

• Cigarettes

• Alcohol

• Marijuana

• Opioids

Prescription Drugs

• Pesticides

• Chlorpyrifos

Low Birthweight (LBW)

Less than 2,500 grams (5 ½ pounds) at birth.

Very Low Birthweight (VLBW)

Under 1,500 grams (3 pounds, 5 ounces) at birth.

Extremely Low Birthweight (ELBW)

Under 1,000 grams (2 pounds, 3 ounces) at birth.

Preterm

Birth occurs at 36 or fewer weeks after conception; associated with LBW