Fetus Critical Period

Critical Period

The critical point in a developing fetus falls roughly within the 5th week and the 6th month. This period is defined as the critical period because beginning around the 5th week tissue begins to differentiate. This specialized tissue starts developing from the top down. Specialized tissues begin forming limbs and digits from the top of the fetus and working its way down to its limbs.

Any agent that causes a birth defect is called a teratogen. Teratogens can vary from chemicals to abnormal heat generated by the mother's body. Defects can be anything from missing limbs to cleft lips or palettes. The degree of severity varies according to the amount of time and the amount of teratogens exposed to.

Alcohol is considered one of the most preventable teratogens, but still effects thousands of babies each year. Fetal Alcohol syndrome is a birth defect caused by consumption of alcohol during pregnancy. The difference between Alcohol and other teratogens such as thalidomide is alcohol attacks the developing brain during the entire pregnancy as opposed to the developing limbs during the critical period. During development of the fetus the brain is constantly developing. This leaves it open to attack from alcohol at all times during the developing months. "Fetal Alcohol Disorders can cause mental retardation, facial deformities, stunted physical and emotional development, behavioral problems, memory deficiencies, attention deficits, impulsiveness, an inability to reason from cause to effect; a failure to comprehend the concept of time; and an inability to tell reality from fantasy."

Thalidomide is an interesting teratogen because it works in a different way from alcohol. Thalidomide was a drug prescribed by doctors to help women deal with morning sickness during pregnancy. The unknown side effects of this drug were it inhibited development of the limbs by stopping blood vessel development. Morning sickness usually starts roughly around the same time the development of the arms takes place. What were happening are women where stopping the morning sickness, but also stopping limb growth of the fetus. "Around 15,000 fetuses were damaged by Thalidomide, of whom about 12,000 in 46 countries were born with birth defects, with only 8,000 of them surviving past the first year of life."

The final teratogen I found is called Isotretinoin also commonly sold under the name accutane. The reason I find this teratogen so interesting is without even knowing of its side effects I have also used it. In the U.S. more than 2,000 women have become pregnant while taking the drug between 1982 and 2003, with most pregnancies ending in abortion. Isotretinoin is most potent during the critical period of a developing fetus. In a study it was found that, two infants with prominent frontal bossing, hydrocephalus, microphthalmia, and small, malformed, low-set, undifferentiated ears were born to mothers who had taken isotretinoin in the first trimester of pregnancy. A Dandy-Walker malformation, microcephaly, hypertelorism, small ear canals, cleft palate, small mouth, and congenital heart disease were also observed. Isotretinoin is a potent teratogen in man; maternal ingestion early in pregnancy leads to a distinct clinical pattern of anomalies." This deeply disturbs me because at the time it was prescribed I remember them not telling me about anything that has to do with pregnancy. If I was married and had a pregnant wife that I let use this I could have caused irreversible damage to my unborn child without even knowing it.

Many moral and ethical issues have arisen because of various advanced imaging tools that allow you see the development of the fetus. The biggest controversy in my opinion is what do you do with a child that you know will be born a teratoma. Regardless if I knew I was having a teratoma baby or a normal baby I would still have it. Only under the most extreme circumstances will the option of not having that child even be considered. Regardless of physical or mental ailments that child is still mine to look after

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