During pregnancy, a problem may occur or a condition may develop to make the pregnancy high risk. For example, pregnant women may be exposed to something that can cause birth defects (teratogens), such as radiation, certain chemicals, drugs, or infections. Or a disorder may develop. Some disorders are related to (are complications of) pregnancy. Other disorders are not directly related to pregnancy (see below). Certain disorders are more likely to occur during pregnancy because of the many changes pregnancy causes in a woman's body.

Drugs

Some drugs taken during pregnancy cause birth defects—see Drug Use During Pregnancy). Examples are isotretinoin (used to treat severe acne), some anticonvulsants, lithium, some antibiotics (such as streptomycin, kanamycin, and tetracycline), thalidomide, warfarin, and angiotensin-converting enzyme (ACE) inhibitors (if taken during the last two trimesters). Taking drugs that block the actions of folate (folic acid), such as the immunosuppressant methotrexate or the antibiotic trimethoprim, can also cause birth defects. A deficiency of folate increases the risk of having a baby with a birth defect. Early in pregnancy, women are asked if they are using any of these drugs.

Women are also asked if they use any recreational drugs. Of particular concern are alcohol, cocaine, and nicotine (in cigarette smoking). All of these drugs can cause miscarriage or cause the baby to be underweight or to have birth defects. These drugs have the following risks:

• Alcohol: The risk of mental retardation (intellectual disability) is increased. Fetal alcohol syndrome is also possible (see Drug Use During Pregnancy: Alcohol).
• Cocaine: The risk of premature detachment of the placenta (placental abruption), premature birth, and stillbirth is increased. The fetus may not grow as much as expected.
• Smoking cigarettes: The risk of stillbirth and pregnancy complications, such as premature labor, placenta previa, placental abruption, and premature rupture of membranes, is increased. The fetus may not grow as much as expected, and children are more likely to have behavioral problems and mental retardation (intellectual disability).

Pregnancy Complications

Pregnancy complications are problems that occur only during pregnancy (see Complications of Pregnancy). They may affect the woman, the fetus, or both and may occur at different times during the pregnancy. For example, complications such as a mislocated placenta (placenta previa) or premature detachment of the placenta from the uterus (placental abruption) can cause bleeding from the vagina during pregnancy. Women who have heavy bleeding are at risk of losing the baby or of going into shock and, if not promptly treated, of dying during labor and delivery.

Last full review/revision December 2008 by Christian M. Briery, MD; John Morrison, MD