How safe is metformin when initiated in early pregnancy? A retrospective 5-year study of pregnant women with gestational diabetes mellitus from India

Abstract Background The initiation of metformin in early pregnancy in Gestational Diabetes mellitus (GDM) remains controversial. The aim of our study was to assess the influence of Metformin on maternal and fetal outcomes when initiated within the first trimester of pregnancy in GDM. Methods and materials A retrospective analysis of 540 women with diabetes complicating pregnancy (IADPSG criteria) over five years (January 2011 to May 2016) was done. The study population comprised of patients initiated on (a) metformin within the first trimester (Group A:n = 186), (b) metformin after the first trimester (Group B:n = 203) and (c) insulin at any time during their pregnancy (Group C:n = 151). The primary outcomes compared were prematurity, respiratory distress, birth trauma, 5-min APGAR score, neonatal hypoglycaemia and need for phototherapy, while secondary outcomes compared were neonatal anthropometric measurements, maternal glycemic control, maternal hypertensive complications, postpartum glucose tolerance. Results Individual and composite primary or secondary outcomes in group A were similar to Groups B and C, though numerically higher premature births were seen in Group A. There was a 1.3% overall incidence of stillbirths/IUD, while 1.11% congenital anomalies were noted of which 2.15% were in group A and 1.32% were in Group C (p = .16). Conclusions The initiation of metformin within the first trimester of pregnancy has no significant adverse maternal or fetal outcomes. However, vigilance for premature births is recommended in women exposed to metformin in early pregnancy.