Although it is recommended to avoid the unnecessary use of drugs during pregnancy, approximately 90% of women take some form of drug while pregnant. These drugs include alcohol, over-the-counter medicines, and prescription drugs. Approximately 3% of congenital malformations are the result of some form of drug use during pregnancy (this does not include alcohol use).
The reason to stop the use of drugs during pregnancy is to prevent teratogenic effects from occurring. A teratogen is an agent that can interrupt the normal development of a fetus.
It is often the case that women need to take medications due to an underlying condition and in these cases, it is necessary for them to comply with their treatment to ensure their health as well as that of their babies. In these special circumstances, it is important for women to talk with their doctors regarding the risks associated with the use of these medications. A health provider should also be notified before a pregnant woman takes any over-the-counter medication, including herbs or other supplements.
Drugs reach the fetus, in utero, by passing through the placenta. There are three ways that a drug can affect the fetus. First, it can harm the fetus by causing it to develop abnormally or can even lead to the fetus’ demise. Second, drugs can affect the placenta and decrease the amount of nutrients the fetus is getting. This results in an underweight infant. Finally, drugs can lead to the premature contraction of the uterine muscles and subsequently cause preterm labor.
Different factors are involved in determining if a drug will cause harm to a fetus. These include how high a dose of the drug the mother is taking as well as how far along she is in her pregnancy. Immediately after fertilization and lasting until around day #20 post-conception, drugs usually act in one of two ways. They either cause fetal demise or cause absolutely no harm to the fetus. During weeks 3-8 postconception, the fetus seems to be more susceptible to the effects of the drug. This is due to the fact that the organs are developing. The fetus can develop a malformation during this time, a miscarriage may occur, or the drug can leave the child completely unaffected. After the organs have developed, drugs usually do not affect the fetus, however, they can affect organ as well as tissue growth and development.
Drugs are currently being categorized by the FDA according to the risk they pose to the fetus. They are assigned a risk category: A, B, C, D, or X. The safest drugs to use during pregnancy are the “A” risk category drugs. Category “A” drugs have been studied using properly designed methods and have proven to pose no obvious risk to the fetus. Category “B” drugs have been studied in animals, but there are no well developed studies in humans. Category “C” drugs have not been studied adequately in either animals or humans; and Category “D” drugs pose a risk to the fetus. However, category “D” drugs are often used if the benefit of using the drug outweighs the risk. Finally, category “X” drugs have proven to be harmful to the fetus and the risk of using these drugs outweighs all benefits.