These days many women are aware of the side effects and contraindications associated with drugs, either prescription or non-prescription medicines, and how it can affect their pregnancy adversely. However, with the list of teratogenic substances growing, it is important to have a greater understanding of how the fetus may be affected rather than just avoiding specific drugs and related substances.
Any substance which can cause developmental malformations in the embryo is known as a teratogen. These may include prescription and over-the counter (OTC) drugs, herbal medicines and supplements, tobacco, alcohol, as well as illegal drugs.
Perhaps the most publicized teratogenic drug known is Thalidomide, which was prescribed and used extensively in the late 50’s and early 60’s for morning sickness in pregnancy. It resulted in the birth of babies with phocomelia (seal-like flippers in place of limbs) and other internal abnormalities and had to be withdrawn from the market.
Drugs reach the fetus through the placenta, in the same way that oxygen and nutrients are delivered to the baby in the mother’s uterus. Depending upon the drug taken, the amount, duration, and stage of pregnancy, it can produce varying effects. Drugs can damage the fetus (resulting in abortion), cause developmental abnormalities (producing birth defects), and result in stillbirth.
A baby is most likely to be born with birth defects if exposed to the harmful effects of drugs during the time when the organs are developing, usually between the third and eighth week of fertilization. This means that sometimes, in very early pregnancy, the fetus may be exposed to harmful substances without a woman being aware that she is pregnant. Drugs taken after this period, although less likely to cause severe birth defects, may contribute to problems with growth and function of normally developed body parts.
According to the degree of risk to the fetus when used in pregnancy, drugs are classified into categories by the Food and Drug Administration (FDA).
Vaccines made of live virus, such as rubella (German measles) and varicella (chicken pox) cannot be given to pregnant women because of their teratogenic effects. However, vaccines for cholera, typhoid, hepatitis A and B, tetanus, diphtheria, plague, and rabies may be given if considered necessary.
The harmful effects of tobacco and alcohol on the growing fetus are many, as are illegal drugs when used during pregnancy. This is discussed further under the dangers of cigarette smoking in pregnancy and dangers of alcohol consumption during pregnancy.
