Birth weight and polycystic ovary syndrome in adult life: a register-based study on 523,757 Danish women born 1973–1991

ObjectiveTo study the association between birth weight and polycystic ovary syndrome (PCOS) in adult life in Danish women born 1973–1991.DesignRegister study.SettingData were extracted from the Danish Medical Birth Register and the Danish National Patient Register (NPR).Patient(s)All female children born of Danish mothers in Denmark between 1973 and 1991 were included (n = 523,757) and followed for a total of 4,739,547 person-years at risk.Intervention(s)None.Main Outcome Measure(s)Information on birth weight was extracted from the Danish Medical Birth Register. The cohort was followed up in the NPR for PCOS diagnoses from age 15 years until the end of 2006. Furthermore, information on maternal diabetes diagnoses was extracted from the NPR.Result(s)The risk of PCOS was significantly increased in women with birth weight ≥4,500 g (incidence rate ratio, 1.57; 95% confidence interval 1.21–2.03) compared to women with birth weight 3,000–3,499 g. All women with birth weight ≥4,500 g were born large for gestational age and a birth weight of 4,500 g represented the 98.5th percentile of the birth weights. Women born of mothers diagnosed with diabetes were at increased risk of PCOS. In these women the risk of PCOS increased with decreasing birth weight.Conclusion(s)The risk of PCOS was increased in women born with birth weight ≥4,500 g. In women of diabetic mothers we found an increased risk of PCOS, which was inversely related to birth weight.