Gestational Diabetes Mellitus in Second Pregnancy by Adverse Outcomes of First Pregnancy: a Population-based Historical Cohort Study.

We investigated combinations of preterm birth, preeclampsia and offspring birthweight by gestational age in a first pregnancy and cross-over risk of gestational diabetes mellitus (GDM) in second pregnancy. The Medical Birth Registry of Norway provided data for 561 873 mothers with first and second births without diabetes prior to second pregnancy, 1985-2020. We combined first pregnancy preterm birth (<37 weeks), preeclampsia and birthweight by gestational age quartiles (Q1-4) into one exposure (16 categories). Relative risks with 95% confidence intervals for GDM in second pregnancy were estimated, keeping mothers with first term birth without preeclampsia and offspring in Q1 as reference. Women with first offsprings in Q4 had high risk of subsequent GDM, however, in combinations with preterm birth and preeclampsia the risk of GDM progressively increased: Compared to 0.9% GDM risk in the reference group, the risk increased to 1.8% for Q4 term births without preeclampsia (aRR 2.1 [95% confidence interval 2.0-2.3]), 2.5% for Q4 preterm births without preeclampsia (aRR 3.3 [2.8-3.8]), 4.2% for Q4 term birth with preeclampsia (aRR 5.6 [4.8-6.4]) and 7.8% for Q4 preterm birth with preeclampsia (aRR 10.1 [7.4-13.7]). Combinations of first pregnancy exposures were associated with a progressive cross-over risk of GDM in second pregnancy.