The use of antidepressants during pregnancy has undergone considerable scrutiny with respect to safety issues, though limited data with respect to dose management and symptom resolution is available. Previous reports on tricyclic antidepressants (TCAs) have demonstrated the need to adjust maternal dose later in pregnancy to maintain therapeutic serum concentrations. However, there is no data on the dosage of selective serotonin uptake inhibitors (SSRIs) required to maintain symptom resolution in women treated for major depression during pregnancy. The purpose of this study, then, was to assess the medication dosage requirements of SSRIs during this time. In this naturalistic study, pregnant women with a primary diagnosis of major depression were followed prospectively through pregnancy at monthly intervals with symptom assessment. Subjects were included in data analysis if they presented prior to 28 weeks gestation, were treated with SSRI monotherapy, received all psychiatric treatment during the pregnancy at the Emory Pregnancy and Postpartum Mood Disorders Program, and achieved euthymia after initial treatment intervention (CGI = 1 and Beck Depression Inventory (BDI) < 9) during pregnancy or failed to respond after eight weeks of treatment. Medication selection was based on personal treatment history or family treatment history (if any), and the published data on SSRIs in pregnancy. All medication dose adjustments were based on depressive symptoms as measured by the BDI and a psychiatric interview (ZNS). Thirty-four pregnant women were included in final analysis. Two thirds of the subjects (n = 22) required an increase in their daily dose of medication to maintain euthymia. The dose increases occurred at 27.1 +/- 7.1 weeks gestation, with mean BDI scores of 16.4 +/- 9.6, compared to a mean treatment response BDI of 6.9 +/- 5.4. Subject's age, education, past personal and familial psychiatric history were not significantly associated with dose adjustment. These novel data on SSRI daily dose in pregnancy parallels the extant literature with tricyclic antidepressants (TCA). Further work to determine the predictors of dose adjustments will provide guidelines for minimizing fetal exposure to both medication and maternal mental illness.