Impact of pharmacological treatment of gestational diabetes on the mode of delivery and birth weight: a nationwide population-based study on a subset of singleton pregnant Portuguese women.

Aims: To access the impact of increasing use of metformin on cesarean section and large for gestational age rates, when compared to insulin.

Methods: A retrospective observational study was developed using data from the Portuguese National Registry, between 2011 and 2019, of 5038 Portuguese women with single pregnancies and gestational diabetes treated with metformin and/or insulin. Three groups were defined according to the therapeutic regimen adopted: g1-insulin in monotherapy (n = 3027[60.1%]); g2-metformin in monotherapy (n = 1366[27.1%]); g3-metformin and insulin (n = 645[12.8%]). Multivariate analysis was adjusted for statistically significant covariates.

Results: The cesarean section rate in g1 was similar to g2 (g1:36.9% vs. g2:37%, p = 0.982), although g3 was associated with cesarean delivery (g3:43.6% vs. g1:36.9%, p = 0.005; g3:43.6% vs. g1:37.0%, p = 0.002), with no differences reported in the multivariate analysis adjusted for year of delivery and pregestational body mass index. A delivery of a large for gestational age newborn was less frequently observed in g2 than in g1 (g2:4.1% vs. g1:5.4%, p = 0.044) and in g3 (g2:4.1% vs. g3:9.1%, p < 0.001), and in g1, when compared to g3 (g1:5.4% vs. g3:9.1%, p < 0.001). In the multivariate analysis, g2 showed lower odds of delivering a large for gestational age newborn, compared to g1 (β = -0.511, OR = 0.596, CI95% = 0.428-0.832, p < 0.001).

Conclusions: The use of metformin was not associated with higher cesarean section rates, compared to insulin. Instead, it was suggested a protective role of metformin on large gestational age rates. The concomitant use of dual therapy suggests more complex pregnancies, requiring closer surveillance that mitigate serious perinatal and obstetrical outcomes.