Fact checked byRichard Smith

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February 16, 2023
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Metformin does not reduce adverse outcomes for pregnancies with type 2 diabetes

Fact checked byRichard Smith
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In pregnancies with type 2 diabetes, metformin plus insulin did not reduce risks for adverse neonatal outcomes compared with placebo plus insulin, according to findings presented at The Pregnancy Meeting.

Perspective from Denice Feig, MD, MSc, FRCPC

“The primary outcome rate was much higher than we anticipated, highlighting the challenges in caring for these patients,” Kim Boggess, MD, professor at the University of North Carolina, Chapel Hill, told Healio. “Also, we did not replicate previous data showing less maternal weight gain in patients who use metformin.”

Kim Boggess, MD, quote
Data were derived from Boggess K, et al. Type 2 diabetes in pregnancy: Effect of metformin added to insulin on neonatal outcome. Presented at: The Pregnancy Meeting; Feb. 6-11, 2023; San Francisco.

Boggess and colleagues conducted a multicenter trial to evaluate the composite outcome —miscarriage, stillbirth, neonatal death, preterm birth, large for gestational age, birth trauma, neonatal hypoglycemia requiring treatment and hyperbilirubinemia requiring phototherapy — among women with type 2 diabetes diagnosed before pregnancy or before 22 weeks’ gestation. Participants were randomly assigned 1:1 to insulin and metformin or insulin and placebo until delivery. The researchers also assessed maternal hypoglycemia and neonatal fat mass at birth.

Each group included 397 participants for analyses. Women in the metformin group had a mean age of 32.8 years; racial/ethnic makeup was 51% Hispanic, 29% Black, 14% white women; 76% had a previous live birth at more than 20 weeks’ gestation; and 93% had used metformin in the past. Among the placebo group, mean age was 33.1 years; racial/ethnic makeup was 53% Hispanic, 27% Black, 14% white women; 86% had a previous live birth at more than 20 weeks’ gestation; and 97% had used metformin in the past.

The composite neonatal outcome occurred at similar rates in the metformin and placebo groups (70% vs. 73%, respectively), as did maternal hypoglycemia (22% vs. 21%). Infant fat mass did not differ between groups.

Neonates in the metformin group were less likely to be born large for gestational age (adjusted OR = 0.66; 95% CI, 0.5-0.92). However, this did not affect the mode of delivery, and there were no differences in the rate of cesarean delivery between groups. There were no differences between groups for babies born small for gestational age.

In subgroup analyses of women with a BMI greater than 30 kg/m2 or pregestational diabetes, there were no differences in composite adverse neonatal outcome, according to the researchers.

Further, there were no differences in maternal or neonatal adverse outcomes between groups.

“For populations comparable to our study group, the use of metformin should be discouraged,” Boggess said.

Future research should focus on long-term follow-up of children born to patients who used metformin for type 2 diabetes, Boggess said.