Metformin to Prevent Late Miscarriage and Preterm Delivery in Women With Polycystic Ovary Syndrome

Inclusion Criteria: * Age: 18-45 years * PCOS diagnosed or reconfirmed according to Rotterdam 2003 criteria, not more than 5 years prior to inclusion * Mode of conception: Any * Single, viable fetus, diagnosed by vaginal ultrasound * Gestational week at inclusion: week 6 + 0 to 12 + 0 * Wash out for metformin: at least 7 days * Able to communicate fluently in the official language at the study cite or English Exclusion Criteria: * Any type of diabetes (except GDM in former pregnancy) * Known liver disease or ALAT \> 100 IU/L * Known kidney disease or creatinine \> 110 μmol/L * Known alcohol or drug abuse * Use of drugs interfering with metformin: erytromycin (or other macrolides), cimetidine, anticoagulation therapy * Unsuitable for participation of other reasons