The contribution of maternal obesity to the risk prediction of pregnancy outcomes in women with gestational diabetes

Abstract

Maternal obesity and gestational diabetes mellitus (GDM) are major contributors to adverse pregnancy outcomes, yet current risk prediction remains largely glucose-focused.

Aims and Methods:

This thesis examined the contribution of maternal obesity and related factors to pregnancy outcomes in women with GDM using systematic reviews and meta-analyses, a Bayesian re-analysis of the Hyperglycemia and Adverse Pregnancy Outcomes (HAPO) study, and population-based cohort analyses of over 450,000 pregnancies from linked NSW datasets. Analyses assessed obesity–GDM interactions, maternal characteristics relative to oral glucose tolerance test (OGTT) values, geographic and hospital-level variation, interpregnancy weight change, and outcomes following bariatric surgery.

Results:

Obesity alone was associated with increased risks of caesarean section, preeclampsia, induction of labour and postpartum haemorrhage, with the highest risks observed when obesity and GDM co-occurred. In the HAPO re-analysis, maternal characteristics, particularly BMI and ethnicity, outperformed OGTT glucose values in predicting caesarean section, preeclampsia and NICU admission. Substantial geographic and hospital-level variation in GDM prevalence and outcomes persisted even after adjustment for case-mix. Interpregnancy weight gain increased risks of large-for-gestational-age (LGA) birth and caesarean section, while weight loss reduced LGA risk but increased small-for-gestational-age and preterm birth, particularly among women with lower baseline BMI. Following bariatric surgery, residual BMI was the predominant driver of adverse outcomes.

Conclusions:

Maternal obesity is a major determinant of pregnancy outcomes in women with GDM, often exceeding the predictive value of glucose measures. Maternal weight trajectories, healthcare variation and bariatric surgery further shape risk. These findings support more integrated approaches to risk prediction and clinical care beyond glucose alone.