Effects of Alcohol on Prenatal Development Term Paper

Excerpt from Term Paper :

Women who drink alcohol during pregnancy risk the health of the fetus and implicitly, the health of the child after birth. There are few studies made on humans in what concerns alcohol and interferences in prenatal development. That is why research is primarily based on animal studies. It is difficult to determine the exact amount of alcohol that can influence the fetus' development in a negative way and that is way women who plan to have a baby or women who found out that are pregnant should stop drinking during their pregnancies. Some of the most important consequences of severe exposure to alcohol during pregnancy are fetal alcohol syndrome or the death of the fetus. These two, are not the only negative effects that the alcohol has on prenatal development. The brain of the fetus and the healthy development of the fetus' body are also affected by alcohol.

When a pregnant woman has a drink, her fetus has one too. "Alcohol, like carbon monoxide from cigarettes, passes easily through the placenta from mother's bloodstream into her baby's blood -- and puts her fetus at risk of having a fetal alcohol spectrum disorder (FASD). The blood alcohol level (BAC) of the fetus becomes equal to or greater than the blood alcohol level of the mother. Because the fetus cannot break down alcohol the way an adult can, its BAC remains high for a longer period of time." (Effects of alcohol on a fetus)

Every part of the body is affected by alcohol exposure: the brain, ears, face, heart, eyes, kidneys and even bones. Alcohol has negative effects on every mechanism of the body. "Rather, alcohol sets in motion many processes at different sites in the developing fetus:

Alcohol can trigger cell death in a number of ways, causing different parts of the fetus to develop abnormally.

Alcohol can disrupt the way nerve cells develop, travel to form different parts of the brain, and function.

By constricting the blood vessels, alcohol interferes with blood flow in the placenta, which hinders the delivery of nutrients and oxygen to the fetus.

Toxic byproducts of alcohol metabolism may become concentrated in the brain and contribute to the development of an FASD." (Ibidem)

For a conceptual distinction the prenatal development was divided into three stages: the predifferentiation period, the period of the embryo, and the period of the fetus. "The conceptus, throughout gestation, is in a continual state of orderly biochemical and structural transition during which new constituents are being formed and spatially rearranged." (Kathleen R. Stratton, Cynthia J. Howe, Frederick C. Battaglia, Institute of Medicine (U.S.). Division of Biobehavioral Sciences and Mental Disorders. Committee to Study Fetal Alcohol Syndrome, National Institute on Alcohol Abuse and Alcoholism (U.S.), page 37) Any teratogenic agents such as alcohol, or drugs, that interfere in the development can cause abnormalities of the body's physics and even of the organs (heart, brain etc.)

Predifferentiation period refers at those six days, in which the oocyte passes the fertilization and inserts itself into endometrium. During this time, the ovum, passes through different mitotic divisions, and becomes a multicellular blastocyst. It seems that during this period the malformations that appear later are not due to alcohol. Researchers showed that a sever amount of alcohol leads to the blastocyst death, and if the alcohol affects only a small number of cells, "regulative mechanism result in repair with no apparent damage." ( Ibidem)

A later study (Padmanabhan and Hameed, 1988) showed "that alcohol exposure on gestation days 1-6 did not influence litter size (implantation), but markedly increased prenatal mortality (resorptions) and resulted in increased placental weights, decreased umbilical cord length, and decreased fetal weight at gestation day 15 in surviving litters." (Ibidem) This research concluded that consumption of alcohol at the beginning of the pregnancy can be lethal to the embryo.

The second conceptual period was named the embryo period. During this time organs and multicellular tissues of various origins and function are beginning to format and later complete themselves. This process starts after the implantation takes place and continues until the eighth week of pregnancy. During the formation of organs, if exposed to alcohol, the embryo will suffer malformations. "The nature of the defects will depend both on the effects of the agent on embryonic cells and the gestation age at the time of exposure." (Idem, page 38)

In contrast with the researches made on the first period, the effects of alcohol during this period had been studied a lot. It had been showed that, exposure to alcohol during this stage leads to cell death. The most vulnerable are neuronal cells. Studies made on mice showed that exposure to alcohol on the seventh and eighth day of gestation leads to craniofacial malformations. These malformations are similar to those seen in fetal alcohol syndrome (FAS). Lemoine was the first who described fetal alcohol syndrome in a medical literature. This happened in 1968 in France. Soon after this, researches from United States published a landmark report in which they described the birth defects of children with alcoholic mothers. Since then fetal alcohol syndrome was acknowledged in almost all countries. "Briefly, FAS refers to a constellation of physical abnormalities, most obvious in the features of the face and in the reduced size of the newborn, and problems of behavior and cognition." (Idem, page 17)

Apart from these anomalies, the brain is also affected (e.g. microcephaly, deficiencies in cerebral hemispheres, lateral ventricles, limbic structures etc.). According to some research ocular defects such as anophthalmia, corneal and lens anomalies, were linked to severe exposure to alcohol on the seventh day of gestation. In contrast, heart anomalies; such as anomalies of great vessels and reduced size of cardiac tube and also skeletal anomalies were linked to the severe exposure of alcohol on the eighth day of gestation.

"It was concluded (Kotch and Sulik, 1992) that alcohol teratogenesis and the patterns of malformations induced at times corresponding to late in the third and early in the fourth week postfertilization in the human can be directly correlated to the selective cytotoxic effects of alcohol coupled with the selective vulnerability of the cells at the margin of the anterior neural folds. In contrast, acute alcohol exposure on gestation days 9 and 10 was found to produce urogenital anomalies (hydronephrosis, hydroureter) (Boggan et al., 1989; Gage and Sulik, 1991; Gilliam and Irtenkauf, 1990; Randall et al., 1989) and limb anomalies involving forelimbs (including ectrodactyly, polydactyly, syndactyly) (Gilliam and Irtenkauf, 1990; Kotch et al., 1992; Randall et al., 1989; Webster et al., 1980, 1983). A much lower incidence of malformations was observed when alcohol exposure was restricted to gestation days 12-14." (Idem, page 38-39)

The last stage named the period of fetus begins when the organogenesis ends and lasts until birth. In this period exposure to alcohol does not lead to considerable malformations. However, this exposure can bring modifications of tissue and damages the developing of the central nervous system (CNS). Also it can hold back the healthy growth of the fetus. These changes do not stop in this stage, but also continue in postnatal period and can go on until the second year of life.

Genetic factors seem to have an important role in what concerns the effects of alcohol exposure. In 1993 Streissguth and Dehaene said that the outcome from monozygotic twins' research was clearer, than those from the dizygotic twins. They analyzed sixteen pairs of twins, five monozygotic twins and eleven dyzigotic twins. While all the monozygotic twins were concordant for verdict, only seven pairs of the dizygotic twins were concordant for verdict. In animal studies that they made, they concluded that not all of them were affected in the same. They deduced that genetic factors can determine the fetal vulnerability to the alcohol exposure, giving sensitivity or resistance to the alcohol exposure…

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