Metformin versus insulin use for treatment of gestational diabetes and delivery by caesarean section: A nationwide Swedish cohort study

Pregnant women who develop gestational diabetes (GDM) are more likely to deliver by caesarean section (CS). Over the last decade, the use of metformin has increased as an alternative to insulin but it’s unknown how this shift in treatment has influenced the mode of delivery. Therefore, the aim of this study was to determine the association between metformin use and CS and delivery of a large-for-gestational age (LGA) infant compared to insulin use for GDM. The Swedish population health registers were linked to identify pregnant women from 2012 to 2016 without preexisting diabetes and with a first filled prescription of insulin or metformin in trimester 2 or 3 (n = 2467), categorized into those treated with insulin only (88%), metformin only (7.6%), or both insulin and metformin (4.3%). Logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (CI). Analyses were adjusted for relevant covariates and stratified by history of CS. The proportion of women using metformin to treat GDM increased from 2.5% in 2012 to over 30% in 2016. Comparing insulin only to metformin only use, no association with delivery by CS (adjusted OR 0.79, 95% CI; 0.54–1.16) and lower odds of delivering a LGA infant (adjusted OR 0.44, 95% CI; 0.26–0.76) was found. Treatment with both insulin and metformin was associated with an increased risk of CS (adjusted OR 1.65, 95% CI; 1.06–2.56), which were more often unplanned. Estimates were further elevated in nulliparous (adjusted OR 2.32, 95% CI; 0.95–5.65) and multiparous women with a history of CS (adjusted OR 2.29, 95% CI; 0.60–8.74) but conclusions could not be drawn given the wide CIs. There was no evidence of a higher association of metformin use alone with CS compared to insulin use for treatment of GDM but a protective effect for delivery of a LGA infant was shown. Women requiring treatment with both insulin and metformin had increased odds for delivery by CS which in turn may indicate that the need for the use of both medications to treat GDM suggests a pregnancy at higher risk.