Subfertility in relation to gestational weight gain and gestational diabetes: the Norwegian Mother, Father and Child Cohort Study

STUDY QUESTION: Do gestational weight gain trajectories and risk of gestational diabetes mellitus (GDM) differ according to the underlying fecundability and use of ART? SUMMARY ANSWER: Women with ART pregnancies experienced slightly different gestational weight gain trajectories than those who conceived spontaneously within 3 months, with a higher weight gain during the second trimester and lower weight gain during the third trimester. WHAT IS KNOWN ALREADY: Use of ART and prolonged time-to-pregnancy (TTP) have both been linked to adverse pregnancy outcomes, including GDM. However, little is known about how gestational weight gain trajectories differ by fecundability or ART conception. STUDY DESIGN, SIZE, DURATION: A cohort study including 69,491 singleton pregnancies contributed by 61,175 women participating in the Norwegian Mother, Father and Child Cohort Study conducted between 1999 and 2008. PARTICIPANTS/MATERIALS, SETTING, METHODS: Pregnancies were categorized by self-reported TTP (≤3 months, 4-6 months, 7-11 months, ≥12 months) and ART conception identified from the Medical Birth Registry of Norway. Body weight was self-reported at four points (pre-pregnancy, ∼16 weeks' gestation, ∼28 weeks, and at the end of pregnancy) and GDM identified in the Medical Birth Registry of Norway. Gestational weight gain trajectories according to TTP and ART were assessed using mixed-effects linear regression and the risk of GDM was estimated with log-binomial regression. MAIN RESULTS AND ROLE OF CHANCE: Across all pregnancies, the adjusted average weekly weight gain was -15 g during the first trimester, 620 g during the second trimester, and 491 g during the third trimester. ART pregnancies showed different weight gain trajectories than spontaneous conceptions, namely, stable weight during the first trimester, higher weight gain during the second trimester, and lower weight gain during the third trimester compared with pregnancies with TTP ≤3 months. A total of 583 pregnancies (0.8%) were complicated by GDM. Longer TTP and ART were associated with a higher risk of GDM. Compared with pregnancies with TTP ≤3 months, the adjusted risk ratio was 1.48 (95% CI: 1.15; 1.90) for TTP ≥12 and 2.39 (95% CI: 1.71; 3.35) for ART pregnancies. LIMITATIONS, REASONS FOR CAUTION: Weight and TTP were self-reported and subject to misclassification. Important metabolic and reproductive confounders, including PCOS, were unavailable. Unmeasured confounding may partly or fully explain the observed associations. WIDER IMPLICATIONS OF THE FINDINGS: Given the weak associations and unmeasured confounding, the results need confirmation before they have clinical implications. STUDY FUNDING/COMPETING INTEREST(S): The study was supported by funding from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Programme (grant 947684). It was also partly supported by the Research Council of Norway (Women's fertility, grant 320656) and its Centres of Excellence Funding Scheme (grant 262700). The authors declare no conflict of interest. TRIAL REGISTRATION NUMBER: N/A.