PRENATAL DEVELOPMENT AND BIRTH

 

In this article, we are going to look at the development of a child right from conception to birth. We hope this article will enrich you with knowledge that will enable you to understand prenatal development and the factors that influence it as well as the birth process. This is the crucial life time for it effects greatly on the entire life after birth in so many ways.

 PERIODS OF PRENATAL DEVELOPMENT

Life begins by the union of two sex cells called gametes and these cells originate from male and female parents. These are spermatozoa and ovum respectively. The cell of a human being has 46 chromosomes, which are arranged into 23 pairs. The union of the gametes is known as conception that results into the formation of a zygote.

Conception takes place when sperm cell(s) from the male unites with an ovum (egg) in the female’s fallopian tube in a process known as fertilisation. By the time the fertilised egg (zygote) ends its three to four days journey through the fallopian tube and reaches the uterus, it has divided into about 12-18 cells. A zygote has a full complement of 46 chromosomes. 

Characteristic of sex is determined by male gametes alone. This is so because male sex chromosomes are XY while female sex chromosomes are XX. For instance the pairing of male Y chromosomes and female X chromosomes will result into a male offspring. Therefore, prenatal period is the time from conception to birth. Prenatal development is divided into 3 main periods: germinal, embryonic and foetal.

1.       The germinal period

This is the first period of prenatal development that occurs in the first two weeks after conception. During this period, a zygote is created, continued cell division takes place and attachment of the zygote to uterine wall also takes place.

The zygote is made up of 100-150 cells a week after conception. The inner and outer layers of the organism are formed at this stage. The blastocyst is the inner layer of cells that develop during the germinal period. These cells later on changes into embryo. The trophoblast is the outer layer of cells that later on provides nutrition and support to the embryo. Also implantation which is attachment of the zygote to the uterine wall occurs ten days after conception.

The embryonic period

This is a period of prenatal development that occurs from 2-8 weeks after cell division. During this stage, the rate of cell division increases, support systems for the cells and some organs are formed. At this stage, the mass of cells changes from zygote to embryo, which forms 3 layers: these are the endoderm which is the inner most layer that develops the digestive and respiratory systems. The mesoderm, which is the middle layer that later on develops into circulatory system, and excretory system. Finally, the ectoderm which is the outermost layer that later on develops into the nervous system, sensory receptors (tongue, nose and eyes) skin parts (hair, nails etc.).

Life support systems for the embryo, which includes the placenta, the umbilical cord and the amnion also develop during this period.

The placenta is the life support system that consists of tissues in which small blood vessels from the mother and the offspring intertwine but are not joined at all. The umbilical cord supports life by providing two arteries and one vein that connects the baby to the placenta. Only very small molecules such as oxygen, water, salt, and food from the mother’s blood pass back and forth between the mother and the infant. The amnion is a bag-like structure filled with fluid in which the developing embryo floats.

 The foetal period

This is the final period of prenatal development that begins two months after conception and lasts for about 7 months. The foetus is active and can move about its arms and legs, opening and closing its mouth besides movements of the head. The face, forehead, eyes, nose, chin, ears can be distinguished. The sex can be identified as male or female. By the end of the 4^th month foetus is about 15 cm long and the growth occurs mostly in the lower parts. By the end of the 5^th month, the foetus is about 27- 32cm in length and weighs about 300g.

Structures of the skin like toe, nails and fingernails are formed. This is the time when the foetus shows preference in particular position in the womb. By the end of the 6^th month, the foetus is 37-45cm long. During this period, the eyes and the eyelids are completely formed and a fine layer of hair covers the head, by the end of the 7^th month, the foetus is about 37 – 45cm long and weighs about 1 ½ kg. At the eighth and 9^th months, the foetus grows longer and weighs about 2kg. In the last two months, fatty tissues develop and the functioning of various organ systems such as heart and kidneys become operational.

Having looked at what happens in the germinal, embryonic and foetal periods we can now explain some of the hazards that occur in the prenatal period.

HAZARDS ASSOCIATED WITH PRENATAL PERIOD

There are serious hazards to development during the relatively short period before birth. These are either physical or psychological. Physical hazards are dangerous but are easily recognised and so they have received more scientific attention. Psychological hazards are equally dangerous because they affect attitudes of the significant people in the society toward the developing child.

Physical hazards: each of the three main subdivisions of the prenatal period involves certain physical hazards. What happens to the foetus in the womb and in the process of its birth, the adequacy of its uterine nutrition, its good or ill fortune at birth with regard to infection or injury, are all considered as important as its heredity.

Miscarriage and abortion: a miscarriage or spontaneous abortion occurs when pregnancy is brought to an end before the developing organism is mature enough to survive outside the womb. It takes place when the embryo separates from the uterine wall and is flushed out by the uterus. Nearly 20% of all pregnancies end in a spontaneous abortion mostly in the first 2-3 months.

Most of the spontaneous abortions take place without mothers’ awareness and perhaps many involve an embryo/foetus that was developing in a normal way. Today’s spontaneous abortion is brought about by abnormalities of the reproductive tract, viral or bacterial infections and sometimes by severe traumas.

Maternal diseases and conditions: maternal disease can result into defects by crossing the placental barrier. These diseases can also be source of damage to the foetus during birth. For instance:

Rubella (German measles): is a maternal disease that damages prenatal development of children. Those born with Rubella may have defects such as mental retardation, blindness, and deafness and heart problems. The greatest danger of this disease is in the 3rd or 4th week of pregnancy, hence it occurs during organogenesis (when organs are formed) however, it can be controlled nowadays through vaccine, which is administered to children. Also, it is advisable for women who plan to have children to first test their blood before they become pregnant to detect presence of the disease.

Syphilis: this is devastative later in prenatal development in 4th or more months after conception. Unlike Rubella that damages organogenesis, syphilis damages organs that have been formed. It causes eye lesions that can result into blindness.

When present at birth, then it may cause problems that affect the central nervous system and gastro-intestinal tract. It is suggested that women should be tested to detect syphilis before pregnancy.

Genital herpes: this may be contracted during birth. New-borns contract the herpes simplex virus II when they are delivered through the birth canal of mothers with genital herpes. Nearly 1/3 of babies delivered through the birth canal die and ¼ become brain damaged. This can be prevented by using caesarean section to keep the virus from infecting the new-born.

HIV/AIDS: today, the number of women with HIV is growing steadily especially in developing countries. Consequently, more children are born exposed and infected with HIV. HIV/AIDS is among the leading cause of death among children between the ages of 1-14 years. Once the immune system of a baby is destroyed then the result is death. There are 3 ways a mother who suffers from HIV/AIDS can infect her offspring.

•          During gestation across the placenta

•          During delivery through contact with maternal blood or fluids.

•          Postpartum through breast-feeding

However, babies born to HIV/AIDS-infected mothers can be placed under the following categories.

•        Those who are infected and symptomatic (showing HIV/AIDS symptoms)

•        Those who are infected and asymptomatic (not showing HIV/AIDS symptoms)

•        Those who are not affected at all.

It is suggested that couples should be tested to detect HIV/AIDS before pregnancy in order to prevent the spread of HIV among children. In addition, a woman who is pregnant and suffers from HIV/AIDS should be put under HIV/AIDS drugs to prevent the foetus from being infected.

Maternal age: this has been revealed to be a condition that facilitates possibility of physical hazards during the prenatal period. The mortality rate of an infant born to adolescent mothers is double that of infants born to mothers in their 20s. This is because mothers in adolescent stage may have less developed reproductive system, poor nutrition, lack of parental care and low socio-economic status. Nowadays, there is delay in child bearing because women want to establish their careers before starting a family. 

This delay can cause Down’s syndrome. Also, as women approach menopause period, they frequently have endocrine disorders that slow down the development of the embryo and foetus and this results in developmental irregularities such as cretinism, Down's Syndrome, heart malformations and hydrocephalus, all of which cause physical and mental defects.

Maternal Malnutrition: this can affect normal development especially of the foetal brain as well as physical aspect. The foetus depends on its mother for nutrition, which comes from the mother’s blood. Nutrition is determined by any specific diet. A pregnant woman requires appropriate level of proteins, vitamins, minerals etc. A woman’s nutrition influences her ability to reproduce and give birth to a healthy child. Otherwise she may stop menstruating hence making conception impossible.

Drugs: excessive smoking and drinking are dangerous to normal development especially during embryonic and foetal periods. Taking the wrong drugs at the wrong time may make an offspring physically handicapped for life for instance, thalidomide when taken during pregnancy might prevent growth of arms and legs. Heavy drinking during pregnancy can lead to deformed limbs, face, heart and mental retardation. Cigarette smoking by pregnant women can cause foetal and neonatal death as well as low birth weights.

Environmental hazards: radiation, chemical and environment pollutants and toxic waste of modem industrial world are dangerous to the foetus. For instance, radiation can cause gene mutation (abrupt but permanent change in genetic material). Fathers who are often exposed to a high level of radiation have higher chances of producing children with chromosomal abnormalities. X-ray can also affect development of embryo during pregnancy. Toxoplasmosis caught from outdoor cats, which feed on raw meat such as rats and mice can cause eye defects, brain defects and premature birth. The toxoplasmosis organism can pass from the cat in its faeces and lives up to one year.

It is therefore suggested that pregnant mothers should wash their hands after handling cats, raw meat etc. and should ensure that meat is thoroughly cooked before being eaten.

Psychological hazards: maternal stress can easily be transmitted to the foetus. When an expectant mother is exposed to intense fears, anxieties and depression, physiological change occurs in respiratory and glandular systems. For instance, due to fear, adrenaline may be produced which restricts blood flow to the uterus and may deprive the foetus of adequate oxygen. The mother’s emotional state during pregnancy can influence the birth process. An emotional mother might develop irregular contractions and a more difficult labour period.