Women given metformin were also less likely to have a baby with a birth weight of 4 kg (8.8 lb) or more, at 12.1% versus 19.2%, or a relative risk of 0.65 (P = .046), and a baby that was extremely large for gestational age, at 8.6% versus 14.8%, or a relative risk of 0.58 (P = .046).