Lithium dosing strategies during pregnancy and the postpartum period.

Background Lithium is challenging to dose during pregnancy. Aims To provide guidance for dosing lithium during pregnancy. Method Retrospective observational cohort study. Data on lithium blood level measurements ( n = 1101), the daily lithium dose, dosing alterations/frequency and creatinine blood levels were obtained from 113 pregnancies of women receiving lithium treatment during pregnancy and the postpartum period. Results Lithium blood levels decreased in the first trimester (-24%, 95% CI -15 to -35), reached a nadir in the second trimester (-36%, 95% CI -27 to -47), increased in the third trimester (-21%, 95% CI -13 to -30) and were still slightly increased postpartum (+9%, 95% CI +2 to +15). Delivery itself was not associated with an acute change in lithium and creatinine blood levels. Conclusions We recommend close monitoring of lithium blood levels until 34 weeks of pregnancy, then weekly until delivery and twice weekly for the first 2 weeks postpartum. We suggest creatinine blood levels are measured to monitor renal clearance.