Although lithium has been used effectively as a medication to treat bipolar and major depressive disorders, there are limited data defining lithium use patterns during pregnancy.

To investigate trends and patterns of lithium prescribing in the perinatal period (before, during and after pregnancy) among pregnancies in the UK.

We conducted a population-based study using primary healthcare records from the Clinical Practice Research Datalink GOLD, analysing 752 112 pregnancies during the period 1995–2018. We assessed the prevalence and patterns of lithium prescriptions, including discontinuation, continuation and dosage. Maternal characteristics were defined for lithium non-users and users, and between those who continued and discontinued use.

From 1995 to 2018, the prevalence of lithium prescribing per 10 000 pregnancies was 3.02 (95% CI: 2.64, 3.44) before pregnancy, 1.89 (95% CI: 1.59, 2.23) during pregnancy and 2.81 (95% CI: 2.44, 3.21) postpartum. Prescribing during pregnancy was low across the study period, with the most recent prevalence in 2018 of 1.03 (95% CI: 0.26, 4.11) per 10 000 pregnancies. Among 337 pregnancies with perinatal lithium prescribing, 48.4% involved a diagnosis of bipolar disorder. Of 227 pregnancies where lithium was prescribed preconception, 15.4% continued treatment throughout pregnancy; discontinuation occurred before pregnancy in 20.7%, and during second or third trimester in 30.8%; 33.0% followed other prescribing patterns. Women who discontinued lithium were more likely to be younger, have a body mass index ≥30 kg/m2, a diagnosis of bipolar disorder, a history of smoking and >10 primary care consultations in the 12 months preconception, compared with those who continued treatment.

Lithium prescribing during pregnancy in the UK is uncommon and discontinuation is frequent, particularly in the later stages of pregnancy. These findings highlight the need for proactive perinatal mental healthcare strategies and close clinical monitoring, to reduce unintentional first-trimester exposure while ensuring continuity of care for maternal mental health.