Dodd JM, et al. - Among overweight and obese pregnant women, researchers evaluated the impacts on maternal and infant outcomes of antenatal metformin (to a maximum dose of 2000 mg per day) given in addition to dietary and lifestyle advice. In addition to dietary and lifestyle advice initiated during 10-20 weeks of gestation, they found that metformin did not improve pregnancy and birth outcomes for pregnant women who were overweight or obese.

Methods

• GRoW was a multicentre, randomised, double-blind, placebo-controlled trial.
• From three public maternity units in Adelaide, SA, Australia, pregnant women at 10–20 weeks' gestation with a BMI of 25 kg/m² or higher were enlisted.
• Women were randomly assigned (1:1) to receive either metformin or matching placebo by means of a computer-generated schedule.
• Study participants, their antenatal care providers, and research staff (including outcome assessors) were masked to treatment allocation.
• All women were given a dietary and lifestyle intervention.
• The proportion of infants with birthweight greater than 4000 g was t he primary outcome.  
• Measures of maternal weight gain, maternal diet and physical activity, maternal pregnancy and birth outcomes, maternal quality of life and emotional wellbeing, and infant birth outcomes were included secondary outcomes.
• The results were analyzed on an intention-to-treat basis (including all randomly assigned women who did not withdraw consent to use their data, and who did not have a miscarriage or termination of pregnancy before 20 weeks' gestation, or a stillbirth).

Results

• According to the findings obtained, of the 524 women assigned randomly between May, 28 2013 and April 26, 2016, 514 were included in outcome analyses (256 in the metformin group and 258 in the placebo group).
• Findings revealed that median gestational age at trial entry was 16·29 weeks (IQR 14·43–18·00) and median BMI was 32·32 kg/m² (28·90–37·10).
• One hundred sixty-seven (32%) participants were overweight and 347 (68%) were obese.
• No significant difference was found in the proportion of infants with birthweight greater than 4000 g (40 [16%] with metformin vs 37 [14%] with placebo; adjusted risk ratio [aRR] 0·97, 95% CI 0·65 to 1·47; p=0·899).
• Data reported that metformin receiving women had lower average weekly gestational weight gain (adjusted mean difference −0·08 kg, 95% CI −0·14 to −0·02; p=0·007) and were more likely to have gestational weight gain below recommendations (aRR 1·46, 95% CI 1·10 to 1·94; p=0·008).
• Between groups, total gestational weight gain, pregnancy and birth outcomes, maternal diet and physical activity, and maternal quality of life and emotional wellbeing did not vary significantly.
• They discovered that similar numbers of women in both treatment groups (76% [159/208] in the metformin group and 73% [144/196] in the placebo group) reported side-effects (ie, nausea, diarrhoea, and vomiting).
• Two stillbirths (placebo group) and one neonatal death (metformin group) occurred.
• None of the perinatal deaths were determined to be attributable to participation in the trial.