Metformin safe in first trimester of pregnancy : BMJ

The researchers in the UK have found that there was no evidence for an increased risk of all non-genetic congenital anomalies combined following exposure to metformin during the first trimester.

Use of metformin in pregnancy remains controversial as it affects stem cell function and has been shown to cross the human placenta at term, exposing the fetus to concentrations approaching those in the maternal circulation. But animal studies have shown no increased risk of a congenital anomaly at therapeutic doses.Dr.Joanne E Given and colleagues conducted an exploratory case-control study to evaluate whether exposure to metformin during the first trimester of pregnancy, for diabetes or other indications, increases the risk of all or specific congenital anomalies. The study has been published in Journal the BMJ.

Metformin has been used in the treatment of type 2 diabetes since the 1950s and in spite of reservations about its use in pregnancy, it has been recommended for use in pregnancy in the UK since 2008 in women with gestational diabetes and in type 2 diabetes when the likely benefits outweigh the potential for harm.

The researchers explored 11 EUROmediCAT European congenital anomaly registries surveying 1 892 482 births in Europe between 2006 and 2013. This exercise involved 50 167 babies affected by congenital anomaly (41 242 non-genetic and 8925 genetic) including live births, fetal deaths from 20 weeks’ gestation, and terminations of pregnancy for fetal anomaly.

It was found that 168 babies affected by congenital anomaly (141 non-genetic and 27 genetic) were exposed to metformin, 3.3 per 1000 births. No evidence was found for a higher proportion of exposure to metformin during the first trimester among babies with all non-genetic anomalies combined compared with genetic controls (adjusted odds ratio 0.84, 95% confidence interval 0.55 to 1.30).

The researchers concluded that No evidence was found for an increased risk of all non-genetic congenital anomalies combined following exposure to metformin during the first trimester, and the one significant association of pulmonary valve atresia was no more than would be expected by chance. They felt that further surveillance is needed to increase sample size and follow up the cardiac signal, but these findings are reassuring given the increasing use of metformin in pregnancy.