Defects in Human Development
1) For instance, when a pregnant woman drinks alcohol her embryo is exposed to similar concentration of alcohol as is in her blood. The alcohol may generate a set of physical and mental abnormalities termed as foetal alcohol syndrome (FAS). In this syndrome prenatal and postnatal growth is retarded. Abnormal facial features, reduced head size and mental retardation are seen. As little as 8.5 ml of alcohol every day or engaging in a single drinking binge by a pregnant woman can result in FAS.
2) Infection through German measles (caused by Rubella virus) in a pregnant woman can cause congenital malformations in the embryo. If the rubella infection is contacted throughout the first four or five weeks of pregnancy, the embryo's eyes, ears and heart may be malformed when exposure to this virus during later stages of development may result in defects in the central nervous system.
3) There are several drugs that are apparently harmless to adults but may be injurious to developing embryos. They are not toxins but teratogens like they lead to malformations in the embryo. Perhaps the most unfortunate example of the effect of teratogens is the drug thalidomide which was used as a tranquilizer. In a couple of years of its introduction over 8000 crippled children with no limbs were take birth in Europe and England.
4) The highest sensitivity to such type of a teratogenic agents is during 18-55 days after conception. The peak period being day 30. Pregnant women must, therefore, never use any drugs without the advice of their attending physicians.