Pregnancy was once thought to be a time of emotional well being during which maternal hormone changes protected against mental illness. Research is making it clear that this is not true. Dr. Cohen said that recent studies have shown equal rates of depression in pregnant and non-pregnant women. Moreover, he stated, studies have been conducted with women who discontinued antidepressant medication in the early stages of pregnancy, and up 75% of women in those studies had suffered depressive relapse before the end of the pregnancy.

This raises the question of risks to both mother and fetus during pregnancy. Dr. Cohen said that there are very good data about the teratogenicity of the tricyclic antidepressants, which demonstrate almost no instances of fetal malformations in infants whose mothers took them during pregnancy. However, few women now use tricyclic antidepressants. Most are now treated with selective serotonin reuptake inhibitors (SSRIs).

Of the SSRIs, the most extensive data come from a manufacturer's registry of patients using fluoxetine during pregnancy. That information suggests that there is no evidence of fetal malformations, even when babies are exposed during the first trimester.

While there is much less information on the safety of other SSRIs, so far there is no indication that they pose risks of fetal malformations, according to Dr. Cohen. Moreover, no problems have been seen in long-term studies of babies born to mothers taking SSRIs. While the fluoxetine registry has followed children for up to seven years, Dr. Cohen stressed that there is not enough data yet to allow definitive conclusions about the long-term safety of SSRIs.

There is ample evidence that most medications are found in breast milk and can be found in a child's blood after breastfeeding. Insufficient data exist to make claims about safety.

Dr. Cohen said that taking medication during pregnancy and breastfeeding is ultimately the decision of the mother. Her doctor should tell her that SSRIs and other psychiatric medicines cross the placenta and are secreted into breast milk. On the other hand, she should be informed of dangers to the baby from maternal relapse into depression during and after pregnancy. Balancing these concerns should lead to what is best for the individual mother.