Background: Bipolar disorder is often associated with a lifetime indication for treatment with psychotropic drugs, thus pregnant women face the dilemma whether to continue treatment or not. This study describes the psychopharmacological drug utilization patterns among women with bipolar disorder from 12 months preconception to 12 months postpartum. Methods: We conducted a register-based cohort study among all Danish women aged 15-55 with a diagnosis of bipolar disorder, who gave birth to their first and singleton child between January 1997 and December 2012. Psychotropic drug use was determined by prescriptions obtained from the Danish National Prescription Registry. Results: We identified 336 women. The proportion of women redeeming prescriptions for any psychotropic drug decreased during pregnancy, from 54.8% in the 3 months preconception to 36.6% in the third trimester (p < 0.001). Lithium dosing increased significantly during pregnancy. A total of 35 (41.2%) of the women on psychotropic monotherapy and 37 (50.0%) of the women on psychotropic polypharmacy used an antidepressant without concomitant use of a mood-stabilizer at some time during pregnancy. Limitations: Only redemption of prescriptions was assessable, thus we were not able to assess compliance and discontinuation of treatment before the end of the treatment duration. There was no information on drug use during hospitalizations. Conclusions: We found a decrease in the proportion of women redeeming prescriptions during pregnancy. There was a high prevalence of antidepressant use without a mood-stabilizer, potentially putting women at risk for a switch to mania - although this is still debated. This calls for further investigation.