Effect of high parity on the occurrence of prediabetes: a cohort study

Objective. To assess the effect of parity on the occurrence of prediabetes defined as an abnormal fasting plasma glucose (5.6-6.9 mmol/l), an abnormal 2-hour oral glucose tolerance test (7.7-11.1 mmol/l), or both, before 12 weeks gestation or at least 6 weeks after delivery. Design. Retrospective cohort study. Setting. Nested on a community trial Delaying the Development of Diabetes Mellitus type 2 (AMAL study) in Oman. Population. 532 women with a total of 3,196 pregnancies. Methods. We conducted sets of Cox proportional hazard regression analyses: crude, age-adjusted and full models which adjusted for maternal age, education, family income and year of delivery. Main outcome measures. Hazard ratio (HR) of the effect of parity on prediabetes. Results. We enumerated 258 cases of prediabetes over 8,529 person-years of follow up. In the crude model, high parity (>= 5) pregnancies carried a higher risk of prediabetes than low parity (<5) pregnancies (HR = 3.72; 95% CI = 2.80, 4.91), and the prediabetes incidence rate increased in a dose-response fashion over multiple categories of parity. In age-only models, the association attenuated with control of the confounding effect of maternal age (HR = 1.05; 95% CI = 0.76, 1.45). Adjusting for other confounders in the full models yielded similar results to those adjusted for maternal age only. Conclusions. The apparent effect of parity on the occurrence of prediabetes is attributable to the confounding effect of maternal age rather than to high parity.