Association of maternal polycystic ovary syndrome and diabetes with preterm birth and offspring birth size: a population-based cohort study

STUDY QUESTION: Is the presence of polycystic ovary syndrome (PCOS) associated with more adverse infant outcomes in mothers with different types of diabetes? SUMMARY ANSWER: The presence of PCOS implies higher risks of total (medically indicated and spontaneously combined) and spontaneous preterm birth in mothers with non-insulin-treated type 2 diabetes and gestational diabetes mellitus (GDM), and lower risk of offspring being large for gestational age (LGA) in mothers with insulin-treated diabetes. WHAT IS KNOWN ALREADY: PCOS is suggested to be an independent risk factor for adverse infant outcomes, and it is highly prevalent in mothers with diabetes. However, the impact of PCOS on the associations of different types of maternal diabetes with preterm birth and offspring birth sizes has not been reported. STUDY DESIGN, SIZE, DURATION: This is a population-based cohort study including all live births between 1996 and 2014 in Finland. Children with concurrent maternal diagnoses that could cause signs and symptoms similar to PCOS were excluded. A total of 1 097 753 children were included. PARTICIPANTS/MATERIALS, SETTING, METHODS: National registries were linked to identify births with maternal PCOS (n = 24 682), stratified by diabetes types. Logistic regression was used to examine the association of maternal PCOS and comorbid insulin-treated diabetes, non-insulin-treated type 2 diabetes or GDM with offspring LGA and small for gestational age (SGA). Generalized estimating equation was used to assess the risk of preterm birth in relation to maternal PCOS and diabetes. Potential interaction between PCOS and diabetes was evaluated on both additive and multiplicative scales. MAIN RESULTS AND THE ROLE OF CHANCE: Using mothers with no PCOS and no diabetes as the reference and adjusting for maternal and birth factors, there were higher risks of total (odds ratio (OR) 2.84, 95% CI 2.21 − 3.66 vs. OR 1.91, 95% CI 1.77 − 2.07, P = 0.01) and spontaneous (OR 4.02, 95% CI 2.94 − 5.50 vs. OR 2.35, 95% CI 2.13 − 2.59, P = 0.001) preterm birth for those with PCOS in mothers with non-insulin-treated type 2 diabetes and higher risks of total (OR 1.42, 95% CI 1.27–1.58 vs. OR 0.89, 95% CI 0.86–0.91, P = 0.0001) and spontaneous (OR 1.80, 95% CI 1.59–2.05 vs. OR 1.01, 95% CI 0.98–1.05, P = 0.0001) preterm birth for those with PCOS in mothers with GDM. Among mothers with type 2 diabetes, further adjusting for maternal BMI eliminated the difference in preterm birth risks between those with and those without PCOS, and adjustment for infertility treatment and pre-eclampsia also reduced the preterm risks associated with PCOS significantly. For mothers with GDM, however, the risks of total and spontaneous preterm birth remained higher for those with PCOS following these aforementioned adjustments or stratified analysis. The risk of offspring being LGA was lower for those with PCOS than those without PCOS among mothers with insulin-treated diabetes (OR 18.90, 95% CI 14.21–25.14 vs. OR 32.04, 95% CI 29.79–34.46, P = 0.0001), showing departure from additivity (relative excess risk due to interaction −11.74, 95% CI −16.17 to −7.31, P < 0.001) and multiplicativity (P < 0.001). PCOS did not alter the risk estimate of preterm birth in mothers with insulin-treated diabetes or offspring LGA and SGA in mothers with type 2 diabetes or GDM. LIMITATIONS, REASONS FOR CAUTION: The register-based diagnoses used in this study captured only women with PCOS seeking medical care and having live births. Including female infertility associated with anovulation as PCOS exposure was a risk for misclassification. Sample sizes for pregestational diabetes were small. Insulin purchase during pregnancy in those without a diabetes diagnosis was not accounted for in the analysis. For patients treated with insulin or other medications, we were unable to assess how they complied with such prescriptions. Also, maternal BMI was recorded only once in early pregnancy, thus the potential influence of gestational weight gain on birth outcomes could not be examined. Data on the causes for preterm birth were not available from the registers. WIDER IMPLICATIONS OF THE FINDINGS: The presence of PCOS implied higher risks of total and spontaneous preterm birth in mothers with type 2 diabetes or GDM, and lower risk of offspring being LGA in mothers with insulin-treated diabetes. The higher risks of preterm birth added by PCOS could be explained by prepregnancy BMI or in part by infertility treatment and pre-eclampsia in maternal non-insulin-treated type 2 diabetes, but not in maternal GDM. The differential effects of PCOS on the associations of different types of maternal diabetes with infant outcomes have implications for preventative strategies and clinical counseling for affected pregnancies. STUDY FUNDING/COMPETING INTEREST(S): This study was supported by Shandong Provincial Natural Science Foundation, China (ZR2020MH064 to X.C.), Shandong Province Medical and Health Technology Development Plan (2018WS338 to X.C.), the joint research funding of Shandong University and Karolinska Institute (SDU-KI-2019-08 to X.C. and C.L.), the Finnish National Institute for Health and Welfare: Drug and pregnancy project (M.G.), the Swedish Research Council (2014-10171 to C.L.), the regional agreement on medical training and clinical research (ALF) between Stockholm County Council and Karolinska Institute Stockholm County Council (SLL20170292 and SLL20190589 to C.L.), the Swedish Brain Foundation (FO2019-0201 and FO2020-0305 to C.L.). X.C. received grants from the China Scholarship Council at the beginning of the study. The authors have no competing interests to disclose. TRIAL REGISTRATION NUMBER: N/A.