Use of metformin and insulin among pregnant women with gestation diabetes in the United Kingdom: A population-based cohort study.

AIMS: The contemporary prescription patterns of antidiabetic drugs following guideline changes recommending metformin as first-line gestational diabetes (GDM) pharmacotherapy is underexplored. We aimed to examined use of metformin and insulin during pregnancy among women with GDM over 20 years in the United Kingdom. METHODS: We conducted a population-based cohort study using linked data from the Clinical Practice Research Datalink, its pregnancy register and Hospital Episode Statistics from 1998 to 2017. We included pregnancies of women without prior diabetes history who received GDM diagnosis or initiated an antidiabetic drug after 20 weeks gestation. Patient-level and practice-level characteristics were compared between metformin initiators and insulin initiators. We described trends of initiating metformin as first-line treatment and described time to initiation of rescue insulin overall, and by body mass index among metformin initiators. RESULTS: Our cohort included 5633 pregnancies from 5393 women with GDM, of whom 38.9% initiated pharmacotherapy (41% insulin, 59% metformin). Metformin prescriptions (as opposed to insulin) increased substantially, from <5% of pregnancies before 2007 to 42.5% in 2008. Over 85% of pregnancies that were prescribed pharmacotherapy were prescribed metformin as first-line treatment in 2015. Among metformin initiators, 16% initiated rescue insulin, typically occurring within 40 days of metformin initiation. Choice of GDM pharmacotherapy varied by characteristics, including smoking, obesity, race/ethnicity and general practice regions. CONCLUSIONS: Metformin was the most prescribed medication for GDM, with large increases over the past 2 decades. The increasing use of oral-antidiabetic drugs during pregnancy, consistent with other regions, highlights the need for future studies examining effectiveness and safety of antidiabetic drug use during pregnancy.