More than 50% of pregnant women take prescription or nonprescription (over-the-counter) drugs or use social drugs (such as tobacco and alcohol) or illicit drugs at some time during pregnancy, and use of drugs during pregnancy is increasing. There are many drugs that can be dangerous for the baby if taken by the mother during pregnancy. In general, drugs should not be used during pregnancy unless necessary because many can harm the fetus. About 2 to 3% of all birth defects result from drugs that are taken to treat a disorder or symptom.
Sometimes drugs are essential for the health of the pregnant woman and the fetus. In such cases, a woman should talk with her doctor or other health care practitioner about the risks and benefits of taking the drug. Before taking any drug (including over-the-counter drugs) or dietary supplement (including medicinal herbs), a pregnant woman should consult her health care practitioner. A health care practitioner may recommend that a woman take certain vitamins and minerals during pregnancy.
Drugs taken by a pregnant woman reach the fetus primarily by crossing the placenta, the same route taken by oxygen and nutrients, which are needed for the fetus’s growth and development. Drugs that a pregnant woman takes during pregnancy can affect the fetus in several ways:
- They can act directly on the fetus, causing damage, abnormal development (leading to birth defects), or death.
- They can alter the function of the placenta, usually by causing blood vessels to narrow (constrict) and thus reducing the supply of oxygen and nutrients to the fetus from the mother. Sometimes the result is a baby that is underweight and underdeveloped.
- They can cause the muscles of the uterus to contract forcefully, indirectly injuring the fetus by reducing its blood supply or triggering preterm labor and delivery.
- They can also affect the fetus indirectly. For example, drugs that lower the mother’s blood pressure may reduce blood flow to the placenta and thus reduce the supply of oxygen and nutrients to the fetus.