Closure before birth forces blood to flow through the lungs, which haven't expanded yet, overloading the fetus' circulatory system. Taking large doses of aspirin may cause bleeding problems in the mother or the newborn. Aspirin or other salicylates may increase bilirubin levels in the fetus' blood, causing jaundice and occasionally brain damage. Antianxiety Drugs and Antidepressants Antianxiety drugs may cause birth defects when taken during the first 3 months of pregnancy, although this effect hasn't been proven. Barbiturates, such as phenobarbital, taken by a pregnant woman tend to reduce the slight jaundice newborns commonly have.
Antibiotics When taken during pregnancy, antibiotics can cause problems.
Tetracycline antibiotics cross the placenta and are stored in the fetus' bones and teeth, where they combine with calcium. As a result, bone growth may be slow, the baby's teeth may be permanently yellow, and the tooth enamel may be soft and abnormally susceptible to cavities. The risk of tooth abnormalities is greatest from the middle to the end of pregnancy. Because several safe alternative antibiotics are available, tetracyclines are avoided during pregnancy. Taking antibiotics such as streptomycin or kanamycin during pregnancy may damage the fetus' inner ear, possibly resulting in deafness.