Lower birth weight in offspring exposed to insulin (− 117.2 g (95% CI − 173.8, − 60.7)) and metformin (− 200.3 g (− 328.5, − 72.1)) compared to offspring not exposed to GDM was partly attributed to lower gestational age at birth and greater proportion of Pakistani mothers in the treatment groups. The gene discussed is INS; the disease is gestational diabetes.