3. Prenatal Development and Birth

Have you ever thought about what an absolute miracle your life is?

You began with two microscopic cells and NOW look at you! You are trillions of cells all working together to allow you to sit up, read, feel, digest, and even, when the time is right, make a miracle of your own.

Development begins with conception. Conception occurs when fertilization creates a zygote, a one-celled organism formed by the union of sperm and an egg. All of the other cells in the human body develop from this single cell.

Prenatal development is the process in which an embryo or fetus gestates during pregnancy, from fertilization until birth.

The Course of Prenatal Development

The prenatal period is divided into three phases:

1.Germinal Stage

This brief stage begins when a zygote is created through fertilization. Within 36 hours, rapid cell division begins, and the zygote becomes a microscopic mass of multiplying cells. This mass of cells slowly migrates along the mother’s fallopian tube to the uterine cavity. On about the seventh day, the cell mass begins to implant itself in the uterine wall.

2. Embryonic Stage

During this stage, most of the vital organs and bodily systems begin to form in the developing organism, which is now called an embryo. Structures such as the heart, spine, and brain emerge gradually as cell division becomes more specialized.

Although the embryo is typically only about an inch long at the end of this stage, it’s already beginning to look human.

3. Fetal Stage

The developing organism, now called a fetus, becomes capable of physical movements as skeletal structures harden. Organs formed in the embryonic stage continue to grow and gradually begin to function. Sex organs start to develop during the third month. The fetus is far from being a passive passenger in its mother’s womb. It kicks, turns, flexes its body, somersaults, squints, and swallows, makes a fist, hiccups and sucks its thumb. It responds to both sound and vibrations, showing that it can hear and feel.

Stages of Prenatal Development

First month: Fertilization occursZygote implants itself in the lining of the uterusRapid cell division occursEmbryonic stage lasts from

2 weeks to 8 weeksCells differentiate into

three distinct layers:    the ectoderm, the mesoderm, and the endoderm

Nervous system begins to develop Embryo is 1/2 inch long

6-Week-Old Embryo (Rear View)

At 6 weeks, the embryo is just over half an inch long. As shown in this photograph, the arms and legs are just beginning to grow, and the head area is extremely large compared to its size after birth. The embryo is shown here in the amniotic sac, which is filled with fluid to protect it.

Heart and blood vessels formHead area develops rapidlyEyes begin to form detailInternal organs grow, especially the digestive systemSex organs develop rapidly and sex is distinguishedArms and legs form and growHeart begins to beat faintlyEmbryo is 1 inch long and weighs 1/10 ounce

Two Months

Head growth occurs rapidlyBone formation begins to form rapidlyThe digestive organs begin to functionArms, legs, and fingers make spontaneous movementsFetus is 3 inches long and weighs 1 ounce

Three Months

4½-Month-Old Fetus Sucking Thumb

At about 4½ months of prenatal development, the fetus is about 10 inches long and weighs approximately 9 ounces. As shown in this photograph, the fetus shows the reflexive movement of sucking its thumb. This activity appears remarkably similar to thumb-sucking in neonates.

Six months

Eyes and eyelids fully formedFat is developing under the skinFetus is 14 inches long and weighs 2 pounds

Nine months

Fetus settles into position for birthThe average baby is more than 19 inches long and weighs nearly 7 pounds now, but babies vary widely in size at this stage

Miscarriage and Abortion

Causes • chromosomal abnormalities• viral or bacterial infections• abnormalities of reproductive tract. • severe trauma

Maternal CharacteristicsMother’s age

- Infants born to adolescents are often premature and mortality rate of infants born to adolescents is double than that of one born to mothers in their 20s.- Babies with down’s syndrome are rarely born to mothers below 30, but the risk is considered higher for mothers below 18.

Nutrition-Nutrition is very important too as children born to malnourished mothers are likely to be malformed.

Emotional states-Stress during pregnancy leads to physiological changes and production of adrenaline(usually in response to fear) which may restrict blood flow to the uterine area and may deprive the fetus of adequate oxygen. -Maternal anxiety during pregnancy was also found associated with infants who were morehyperactive and irritable along with feeding and sleeping problems.

Teratology and Hazards to prenatal Development

The field of study that investigates the causes of birth defects is called teratology. Teratogen is any agent that causes a birth defect.

The probability of structural defects is greatest early in the embryonic period; during the fetal period they are likely to stunt growth or create problems in the way organs function.

For example, brain is most vulnerable at 15-25 daysafter conception; eyes 24-40 days; heart at 24-40 days, and legs at 24-36 days.

Maternal Diseases and Conditions

Rubella, syphilis and genital herpes are found to cause death or deformities in children born to mothers who are infected.

AIDS• Mothers can infect their offsprings: (1)during gestation across the placenta; (2) during delivery through contact with blood or fluids; (3) post-partum through breast-feeding.

• Approximately one-third born to infected mothers will ultimately become infected.• Babies can be infected and symptomatic; infected but asymptomatic and not infected at all.

Drugs• Tranquilizers like thalidomide, taken for morning sickness are known to cause devastating effects on fetus. e.g. if a woman took on day 26, an arm might not grow.

• Fetal alcohol syndrome (FAS) is a cluster of abnormalities that appear in the offspring of mothers who drink heavily during pregnancy.

Fetal and neonatal deaths are higher among smoking mothers; studies have also shown that exposure to smoking was related to poor language and cognitive development; mothers who smoked during pregnancy had infants who were awake more on a consistent basis; and respiratory problems and sudden infant death/ crib death were found very common among the offsprings of mothers who smoked during pregnancy.

Environmental Hazards

Radiation can cause gene mutation, an abrupt but permanent change in genetic material. Even radiation from X-rays can affect the fetus.

BirthStages of Birth:.

Stage 1(average of 12-24 hrs)

uterine contractions are 15 - 20 mins apart and lasts upto a min; contractions come closer as it progresses increasing in intensity; and dilates the cervix to an opening of 4“ for baby to move from uterus to birth canal.

Stage 2(lasts 1 and half hrs.)

head starts to move through the cervix and birth canal.

Stage 3/ Afterbirth

placenta, umbilical cord and other membrane are detached and expelled.

Delivery Complications

• Precipitate delivery is a delivery that takes place too rapidly - takes less than 10 minutes to be squeezed through the birth canal. It can disturb infant’s normal flow of blood and the pressure on infant’s head can causehaemorrhaging.

• If delivery takes too long, anoxia or the insufficient supply of oxygen to the infant can take place. Anoxia can cause brain damage.

The breech position can cause respiratory problems and some cannot pass through the cervix and has to be delivered by a cesarean section

The Postpartum Period

It is a time when a woman’s body adjusts, both physically and psychologically, having completed the process of childbearing.

Physical adjustment:Involution is the process by which the uterus returns to its pre-pregnancy size 5 or 6 weeks after birth. Nursing the baby helps to contract the uterus at a rapid rate.

Emotional and Psychological Adjustments: Many women undergo a postpartum depression and can have a considerable effect on the infant.