PRENATAL DEVELOPMENT AND RISK FACTORS Human development refers to advancement in terms of the acquisition of skills, functions and complexities. In this paper, I aim at discussing and presenting the : (a) Major periods and development of pregnancy from conception to birth (b) Percentages of pregnancies that result in living new born babies (c) Pre-natal stage when the developing organism is more at risk of birth defects and four categories of teratogens (d) Difference between a low birth weight baby and a small for gestation age baby (e) the process of a normal uncompleted birth and tests for assessing the new born condition In order to understand prenatal development of pregnancy, it is vital to mention the biology of how a child comes into existence. Conception begins when a man has to release millions of sperms in an ejaculation during the act of sexual intercourse with a woman. During intercourse a man's semen may be about 300,000 spermatozoa which are released into the vaginal canal. A woman releases one ovum (egg) once every lunar month. Occasionally she may release two ova. Fertilization of eggs happens in the ovulation period. Thus, each particular sperm of the man has one chance in several millions of fertilizing an ovum. It is not possible to determine before conception what sperm will fertilize what ovum. It always involves a sort of gamble and only one sperm (out of a possible million) succeeds in uniting with the ovum. A man determines the sex of a child. A man carries two types of sperms in equal members one type carries twenty-three pairs of chromosomes while the other carries twenty-two pairs of X chromosomes plus one pair of Y chromosomes. A woman's ovum carries twenty-three pairs of X chromosomes. There are four major periods of pregnancy development; prenatal, germinal and the embroyonic stage. Conception is the beginning of life. Prenatal period of pregnancy is the first stage which begins from the time that a child is conceived until it is born roughly nine calendar months. The growth pattern at this stage is mainly physiological. The first sign of pregnancy is the missing of the monthly menstral flow. Before birth, the child passes through the following stages of development in the mother's womb. The Germinal period of pregnancy starts from the time of conception till the second week of pregnancy. At time of conception, the sperm fertilizers the ovum to form the zygote which multiplies by two through the process of cell division. Only twenty-three pairs of chromosomes form a new zygote which continues to develop in a special sack called placenta. The child is attached to the mother through the umbilical cord to the placenta. The child's blood does not mingle with the mother's blood. The umbilical arteries carry blood back to the fetus loaded with wastes and carbon dioxide while the vein returns renewed blood to the fetal circulation. The embroyonic stage of pregnancy starts at the beginning of the third week to the end of the eighth week. As an embryo, the child develops three microscopic layers viz (i) The ectoderm (outer layer) which forms the future skin and nervous system (ii) The entoderm (inner layer) which develops into the mouth, throat and digestive system (iii) The mesoderm (middle layer) which forms supporting tissues, the skeletal system and muscles Signs of pregnancy include, morning sickness, enlargement of breast, darkening of the nipples, frequent urination, giddiness and nausea. The Fetus stage begins from the eighth week until birth. During the third lunar month, the fetus grows to a length of three inches and weighs an ounce. The fetus continues to grow from one lunar month to another until it is born at the end of the nine calendar month. At this stage, the child is subject to prenatal environmental influences. In the United States, approximately thirty per cent of pregnancies that resulted in living newborn babies survived at twenty-three weeks. Fifty to sixty percent born at twenty- four weeks survived. Seventy-five percent born at twenty-five weeks and ninety percent born at twenty-seven to twenty-eight weeks also survived. In some cases, an unborn child is more at risk for developing birth defects. Some diagnostic tests used during pregnancy carry a risk. For instance, women who undergo fetoscopy have miscarriages. Fetal alcoholic syndrome characterized by growth retardation of prenatal origin affects infants born of alcoholic women. When a woman is exposed to severe radiation during the first twenty weeks of her pregnancy, the baby will be born with gross deformities. Approximately three to six percent of all fetus have some sort of birth defect that is fatal at birth or that cause permanent disability. For example, if the pregnant woman is subject to German measles, the unborn child may develop anomalies such as motor difficulties, blindness and deafness. Prenatal exposure to various medications can also result in abnormalities. Common drugs that have teratogenic effects include antibiotics (e.g tetracycline), yellow fever vaccine, pepcid-used to treat ulcers, alcohol and thyroid, phenytoin, progesterone -estrogens, lithium and warfarin. Once again, teratogenic are chemicals, drugs or infections that cause harm to the development of a fetus, a monster that can be in the environment. However, the U.S Public Health Service recommend that women take folic acid which is a B vitamin before and after pregnancy to prevent spine and brain defects in the developing organism and increase chances of having a healthy baby. The average new born weighs about 3,400 grams (71/2 pounds). Low weight babies (LWB) are births that are less than 2,500g regardless of gestation age. Small gestation age(SGA) babies are considered smaller in size for normal gestational age. They have a birth weight that is less than 10th centile. The two terms are related but not synonyms. Premature infants are defined as those weighing between 1,000 and 2,500g. Pregnant women faced with poverty are likely to deliver irritable and low birth weight babies. A strong correlation was discovered between LWB and babies born to disadvantaged families. It was considered a critical aspect of poverty. According to the U.S CDC report, high rates of premature babies are born due to poor prenatal care. In Ireland, a longitudinal report(1999) showed that babies born to parents who were unemployed were twice at risk of having low birth weight babies compared to parents who were fully employed and high professionals. The next thing to know is the process of uncomplicated birth which is categorized into three stages of labor - the beginning of rhythmic contractions. The first stage is the thinning and dilation of the cervix. This process leads to the descent and expulsion of the infant, placenta and membranes from the uterus. What happens after delivery? Preliminary screening tests are conducted after delivery on the baby to check for any disorder. This is not evident on the first day of birth but visible after two or more days. Blood is drawn from the baby to test for heart defects. Ear and eye screening are also conducted. Conclusion Life begins at conception, when fertilization take place as a result of the fusion of the male sperm and the female egg in the uterus. After implantation, the egg begins to divide and at this time, it is known as embryo. Growth and development occur at a rapid pace by the end of eight weeks, the shape is recognizable human, and the embryo has become a fetus. Both heredity and environment influence a child from the time of his conception till his death. References: 1. CDC. Trends in infant mortality attributable to birth defects - United States, 1980 1995 MMWR 1998 47: 77 2. Kathleen Bergers, ''The Developing Person through Childhood and Adolescence'' 3. World Health Organization estimates based on data collected around 1999.
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