Parity and risk of diabetes in a Danish nationwide birth cohort.

AIMS The purpose was to elucidate the association between parity and the incidence of diabetes using national register data. METHODS The study population consisted of all Danish women with a singleton delivery in 1982/1983 (n = 100,669), who subsequently had 74,966 deliveries. The included women were followed up via registries until the end of 2006 for subsequent deliveries, diagnosis of diabetes and death/emigration. RESULTS A total of 2021 cases (2.0%) were diagnosed with diabetes in connection with hospitalization or outpatient treatment during follow-up. Analyses were adjusted for fetal weight and duration of gestation, both at index pregnancy. Cox regression analysis with parity as a time-varying exposure, stratified in two age groups, showed an association between parity and risk of a diagnosis of diabetes. In women <33 years of age, parity 2, 3 and 4 + were associated with an increased risk of being diagnosed with diabetes compared with parity 1 [relative risks: 1.6 (95% confidence interval 1.1-2.3), 2.8 (1.8-4.3) and 2.5 (1.3-4.8), respectively]. Among women >33 years of age, parity 2 was associated with a significantly lower risk of diabetes diagnosis compared with parity 1, whereas parity 4 + was associated with a significantly higher risk of diabetes diagnosis compared with parity 1. CONCLUSIONS The study shows that the risk of diabetes diagnosis increases with parity in young Danish women. This may support a causal association between diabetes and parity.