What do systematic reviews say?

Metformin vs placebo

Metformin showed no clear difference in large‐for‐gestational‐age infant, defined as birthweight ≥ 90th… compared with placebo (high certainty).

• Metformin for women who are overweight or obese during pregnancy for improving maternal and infant outcomes 2018 · Cochrane Headline outcomes only
  RR 0.95 [0.7, 1.3]
  2 studies · 831 participants
  High