Section 3.1 Prenatal development

1. Germinal stage

This stage of human development begins with conception and ends when the zygote is implanted in the wall of the uterus. It typically lasts for the first two weeks after conception. At the moment of conception, two single cells, one from a male (sperm) and one from a female (ovum), merge to form a new cell called a zygote.

After conception, the zygote begins its journey, spending about a week floating down the fallopian tube toward the uterus. Cell division begins approximately 24 to 36 hours after fertilization. Within two to three days, the multiplying cells form a mass that contains several dozen cells and is roughly the size of a pinhead.

Around four days after conception, this mass of cells is referred to as a blastocyst, which starts to take a spherical shape with two layers of cells surrounding a hollow center. The outer layer of the blastocyst will develop into structures that support the growing organism, such as the placenta, while the inner layer will eventually become the embryo.

The final step of this stage is implantation, during which the blastocyst attaches itself to the wall of the uterus. This process is usually complete within 10 to 14 days after conception, by which time the blastocyst contains about 150 cells and is ready to begin the next stage of prenatal development.

2. Embryonic stage

The embryonic stage begins after the fertilized egg attaches to the mother’s uterine wall and lasts from about the 2nd to the 8th week after conception. This is a critical period of development, as the foundations of all major body systems are established.

By week 4, the placenta is fully formed. It serves a vital role by delivering oxygen and nutrients from the mother to the developing baby while also removing waste products. During this time, organ development, or organogenesis, begins, with the formation of the skin, muscles, nerves, heart, and other organs.

A heartbeat can typically be detected around week 4. The baby also starts to form lungs and small limb buds, which will later develop into arms and legs. As the stage progresses, early shapes of fingers, toes, eyes, nose, mouth, and ears become visible, and the nervous system starts to develop.

By the end of the embryonic stage, around week 8, the baby’s major organs have formed, and bones begin to grow, signaling the transition into the next phase of prenatal development which is the fetal stage.

3. Foetal stage

The fetal stage is the final phase of prenatal development, beginning around the 8th week after conception and continuing until birth. At this point, the developing organism is referred to as a fetus. This stage is marked by rapid physical growth, as the fetus increases in size from about 1 inch and 1/4 ounce to an average birth weight of around 7 pounds and a length of approximately 20 inches.

Throughout this stage, all of the organ systems formed during earlier development undergo further refinement and maturation to prepare for life outside the womb. One of the most critical milestones during this period is the achievement of viability, or the fetus’s ability to survive independently outside the womb. This can occur as early as 23 weeks, though most medical experts consider 24 weeks as the average threshold, primarily due to improved lung and brain development.

Brain development is especially significant during the fetal stage. Between the 10th and 18th weeks, brain cells multiply rapidly, laying the foundation for neurological function after birth. The continued growth and specialization of the brain and other vital systems ensure that the fetus is equipped to respond to its environment and sustain life once born.

3.1. Behaviour of a fetus

Fetal behaviors that can be observed include:

•    Responding to sounds with heart rate changes, head turns, and body movements as early as 25 weeks.

•    Distinguishing between familiar and novel stimuli by 32^nd or 33^rd week.

•    Learning in the womb, as evidenced by infants remembering stimuli like maternal heartbeats, amniotic fluid odor, and stories heard prenatally.

•    Exhibiting individual differences in activity levels, with very active fetuses tending to become very active infants, and less active fetuses being more likely to have mental retardation.

•    Male fetuses are more physically active overall due to being awake more often, but activity levels are equal during wakefulness. Female fetuses are more responsive to external stimuli.

4. Factors affecting prenatal development

Prenatal development can be affected by many things that happen before and during pregnancy. These factors can influence the baby’s health and development in the womb and even after birth.

4.1. Physical hazards

Injuries to the mother during pregnancy, such as accidents, can harm the baby. This may cause damage to the placenta, reduce blood flow, trigger early labor, or lead to miscarriage or birth defects.

4.2. Miscarriage

This is the loss of a baby in the early months of pregnancy, often caused by infections, hormonal issues, or physical problems in the mother. It can be emotionally painful and may need medical care.

4.3. Diseases in the mother:

• HIV/AIDS: Can be passed to the baby, but proper treatment can prevent this.
• Genital Herpes: Can infect the baby during birth, causing serious problems like brain or eye damage.
• Syphilis: Can harm the baby if untreated, causing birth defects or miscarriage.
• Rubella: If caught early in pregnancy, it can cause deafness, heart problems, or disabilities in the baby. It can be prevented with vaccination before pregnancy.

4.4. Mother's age

Teen mothers and older mothers face more risks. Teen moms may have babies with low birth weight or other health issues. Older moms have a higher chance of having babies with genetic problems like Down syndrome.

4.5. Poor nutrition

If a mother eats poorly during pregnancy, the baby may have weak bones, poor brain development, low birth weight, and be more likely to get sick.

4.6. Drugs and alcohol

Smoking, drinking alcohol, or using drugs during pregnancy can cause birth defects, brain damage, low birth weight, or long-term problems in the baby’s learning and behavior.

4.7. Environmental hazards

Exposure to harmful things like radiation, chemicals, or infections from animals (like toxoplasmosis from cats) can damage the baby’s brain, cause early birth, or lead to birth defects.

4.8. Emotional stress

Too much stress in the mother can reduce oxygen and nutrients to the baby, leading to slow growth, early birth, or later emotional and learning problems for the child.

5. The birth process

Birth usually happens around 38 to 40 weeks of pregnancy and includes three main stages:

•    Labor (dilation stage): The cervix (opening of the uterus) slowly opens (dilates) to about 10 cm. Contractions become stronger and closer together. This stage can last several hours, especially for firsttime mothers.

•    Delivery (expulsion stage): Once the cervix is fully dilated, the baby is pushed through the birth canal. This stage ends when the baby is completely born.

•    Afterbirth (placental stage): After the baby is born, the placenta (which nourished the baby during pregnancy) is pushed out of the uterus. This usually happens within 30 minutes after delivery.

6. Birth and delivery complications

Sometimes, complications may occur during birth and may require medical attention.

•    Breech position: The baby is positioned with the feet or buttocks first instead of the head. This abnormal position often requires a cesarean section to safely deliver the baby.

•    Prolonged labor: Labor that takes too long can be dangerous for both the mother and the baby. In such cases, medical interventions like inducing labor or performing a cesarean section may be necessary.

•    Umbilical cord problems: The umbilical cord may wrap around the baby’s neck or become compressed, which can reduce the baby’s oxygen supply. This situation can be life-threatening and may lead to an emergency delivery.

•    Excessive bleeding: The mother may experience significant blood loss, especially during the delivery of the placenta. This condition requires immediate medical attention to prevent further complications.