HIGHER pre-pregnancy BMI may increase the risk of pre-eclampsia and preterm delivery among women with type 2 diabetes, according to an Australian study examining pregnancy outcomes in women with pre-existing diabetes.
Researchers analysed 264 singleton pregnancies affected by Type 1 diabetes (T1DM) or Type 2 diabetes (T2DM). Associations differed between the separately analysed groups, with higher BMI linked to poorer early glycaemic control and greater odds of caesarean delivery among women with T1DM, while increasing BMI was associated with pre-eclampsia and preterm delivery in those with T2DM.
Examining Weight and Pregestational Diabetes
Pregnancies complicated by pre-existing diabetes already carry an elevated risk of adverse outcomes. Meanwhile, overweight and obesity are increasingly common among people with both T1DM and T2DM.
Researchers conducted a retrospective analysis of prospectively collected data from a quaternary hospital in metropolitan Sydney, Australia. The study covered pregnancies managed between 2010 and 2019.
The analysis included 264 singleton pregnancies, comprising 124 affected by T1DM and 140 by T2DM. Among women with T1DM, 46% had overweight or obesity, compared with 90% of those with T2DM.
The co-primary outcomes were pre-eclampsia, preterm delivery and infants born large for gestational age (LGA). Investigators analysed T1DM and T2DM separately and examined BMI both categorically and as a continuous measure.
BMI Associated With Risks in Type 2 Diabetes
Among women with T2DM, pre-eclampsia occurred in 20.5% of those with obesity, compared with 2.7% with overweight and 7.7% with normal weight.
After adjustment for potential confounders, every 1 kg/m² increase in BMI above the ethnicity-adjusted upper limit of the normal range was associated with an 8.2% increase in the odds of pre-eclampsia (aOR: 1.082; 95% CI: 1.024–1.144).
A similar pattern emerged for preterm delivery. Rates were 42.2% among women with T2DM and obesity and 30.6% among those with overweight; none of the 13 evaluable women in the normal-weight group experienced preterm delivery.
Each additional 1 kg/m² of BMI above the ethnicity-adjusted normal range was associated with a 4.2% increase in the adjusted odds of preterm delivery (aOR: 1.042; 95% CI: 1.001–1.084).
LGA births also differed across BMI categories in T2DM, occurring in 28.9% of pregnancies affected by maternal obesity compared with 17.1% with overweight and none in the normal-weight group. However, the association between increasing BMI and LGA was no longer statistically significant after adjustment for potential confounders.
Different Associations Observed in Type 1 Diabetes
The researchers did not identify associations between increasing BMI and the three co-primary outcomes of pre-eclampsia, preterm delivery or LGA among women with T1DM.
Higher BMI was, however, associated with poorer early glycaemic target attainment.
First-trimester HbA1c exceeded 6.5% in 45.5% of normal-weight women, 73.2% of women with overweight and 78.6% of those with obesity. Compared with normal weight, overweight was associated with almost three-fold higher adjusted odds of exceeding this target (aOR: 2.995; 95% CI: 1.246–7.202), while obesity was associated with approximately four-fold higher odds (aOR: 4.114; 95% CI: 1.036–16.332).
Increasing BMI in T1DM was also associated with greater odds of excessive gestational weight gain and caesarean delivery.
Findings Require Confirmation
The authors stressed that the regression analyses were exploratory and hypothesis-generating rather than confirmatory.
The single-centre study included relatively few women with obesity in the T1DM group and few normal-weight women with T2DM, limiting statistical power. The researchers also could not comprehensively adjust some analyses for multiple potential confounders and lacked routinely available preconception glycaemic and continuous glucose-monitoring data.
Larger studies are therefore needed to directly compare how maternal overweight and obesity influence pregnancy outcomes in women with T1DM and T2DM.
Reference
Zhen XM et al. Exploring the associations of overweight and obesity with pregnancy outcomes in type 1 and type 2 diabetes: An Australian retrospective cohort study. Journal of Diabetes Investigation. Published 1 October 2026. doi:10.1111/jdi.70440.
