Objectives: The primary objective of this multicenter study is to evaluate the relative impact of insulin resistance (IR) and body mass index (BMI) in women with polycystic ovary syndrome (PCOS) on (1) Key hemodynamic/thrombogenic variables, (2) Oocyte quality and early embryo development, (3) Fetal growth, placental function and adverse obstetric outcome. Secondary objective: To establish a PCOS database and biobank facilitating future basic and interventional research related to PCOS. Design: A cross-sectional and longitudinal cohort study at four University Hospitals in Denmark. Population inclusion: About 200 women fulfilling the Rotterdam Criteria and 100 women without PCOS recruited from 2010 to 2012. Methods: The impact of PCOS, as well as the impact of IR and BMI on the hormonal, metabolic and hemostatic key variables will be analyzed combining conventional, molecular techniques and selected gene analysis. Oocytes will be characterized by gene expression of granulosa and cumulus cells and the early embryo development will be followed by time lapse microscopy. Fetal growth will be assessed by repeated ultrasound measurements, and the pregnancy outcome compared to maternal and fetal biochemical markers of growth and inflammation and clinical pregnancy complications. Main outcome measures: Metabolic and hemostatic risk-biomarkers, oocyte and embryo quality, adverse pregnancy outcome, fetal growth and placental function in women with PCOS.