Continuing Metformin and Adding Insulin for T2D in Pregnancy Does Not Alter Risk for Nonlive Birth or Live Birth With Congenital Malformations

Jun 19, 2024

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Continuing metformin and adding insulin in early pregnancy does not significantly alter the risk for nonlive birth or live birth with congenital malformations compared with switching to insulin monotherapy, according to a study published online June 18 in the Annals of Internal Medicine.

Yu-Han Chiu, M.D., Sc.D., from the Harvard T.H. Chan School of Public Health in Boston, and colleagues examined the teratogenicity of metformin use in the first trimester of pregnancy in an observational cohort study of 12,489 pregnant women with pregestational type 2 diabetes receiving metformin monotherapy before the last menstrual period (LMP). Two treatment strategies were assessed: insulin monotherapy (discontinue metformin and initiate insulin within 90 days of LMP; 850 women) and insulin plus metformin (continue metformin and initiate insulin within 90 days of LMP; 1,557 women).

The researchers found that the estimated risk for nonlive birth was 32.7 and 34.3 percent under insulin monotherapy and insulin plus metformin, respectively (risk ratio, 1.02; 95 percent confidence interval, 1.01 to 1.04). The estimated risk for live birth with congenital malformations was 8.0 and 5.7 percent under insulin monotherapy and insulin plus metformin, respectively (risk ratio, 0.72; 95 percent confidence interval, 0.51 to 1.09).

“Current recommendations of switching from metformin to insulin before pregnancy for the management of type 2 diabetes in pregnancy based on teratogenicity concerns may require reconsideration,” the authors write.

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