To the Editor: Women with bipolar disorder are at especially high risk for relapse during the postpartum period, when the risk for recurrent postpartum mood episodes has been reported to be 25%–40% (1). Because of this high risk of relapse, postpartum prophylactic treatment has been advocated for most patients (2). Our preliminary data emphasize the recurrent nature of postpartum episodes in women with bipolar disorder.

Twenty-eight consecutively selected female patients with bipolar disorder were asked to respond to a structured interview regarding the impact of reproductive events on the course of their illness. After written informed consent was obtained, diagnosis was determined by using the Structured Clinical Interview for DSM-IV. Patients were then systematically asked about mood symptoms and episodes after childbirth.

In our study group, 17 (61%) of the women had at least one child, and 12 (71%) of the 17 described at least one postpartum mood episode. The polarity of the group’s postpartum episodes was exclusively depressive. Notably, the risk of having a postpartum depressive episode increased with successive pregnancies. Of the women who had more than one child and experienced at least one depressive postpartum episode but did not experience depressive episodes after every delivery (N=6), there was a significant relationship between number of births and depressive episodes. Women were more likely to have postpartum depressive episodes after the birth of a second child than after their first (p=0.02, McNemar’s test). In fact, if a woman experienced postpartum depression after some but not all of her pregnancies, it was only after the first pregnancy that she was spared. In the 12 women with more than one child, of those women who experienced a postpartum episode after their first child, the postpartum recurrence rate was 100%.

Although having experienced a postpartum mood episode was predictive of future postpartum episodes, not having experienced a mood episode after the birth of a first child was not protective. Of the nine women who did not experience a depressive episode after the birth of their first child and who later had more children, six (67%) experienced subsequent postpartum depression. Our preliminary findings suggest a significant relationship between risk of development of a postpartum depressive episode and number of pregnancies in women with bipolar disorder. This higher risk may be attributed to hormonal or biochemical factors, older age or longer duration of illness, or greater psychosocial stressors after later pregnancies.