Asthma, gestational diabetes mellitus and adverse perinatal outcomes: an Australian population-based analysis

<bold>Background:</bold> Gestational diabetes mellitus (GDM) is more common in women with asthma. However, no studies have investigated whether concomitant diagnoses of asthma and GDM alters perinatal outcomes. <bold>Methods:</bold> Using a retrospective observational study design, data were collected from electronic obstetric records. Women with singleton births, between 2018-2020, aged >18 years, from antenatal clinics in two local health districts (New South Wales, Australia), were included. Associations between maternal asthma, GDM, and asthma + GDM (vs neither) and 9 adverse outcomes were examined using multivariate regression. Multiplicative interaction between asthma and GDM was also tested. <bold>Results:</bold> We included 25,432 singleton pregnancies: 9.9% with asthma only, 9.8% with GDM only, and 1.4% with asthma + GDM. Asthma (vs neither exposure) was significantly associated with lower birth weight (mean -45 g; 95% CI [−73, -18]). GDM (vs neither) was associated with respiratory distress syndrome (RDS, adjusted relative risk [aRR] 1.26; 95% CI [1.14, 1.40]), hypertensive disorders of pregnancy (HDP, aRR 1.32; 95% CI [1.16, 1.60]) and caesarean birth (aRR 1.18; 95% CI [1.12, 1.24]). For joint exposures (asthma + GDM vs neither), increased risk was observed for several outcomes, notably RDS (aRR 1.40; 95% CI [1.10-1.79]) and HDP (aRR 1.55; 95% CI [1.16-2.06]). There was no evidence of multiplicative interaction between asthma and GDM. <bold>Conclusion:</bold> GDM increased adverse outcomes in this sample of Australian pregnancies. Increased risk was also detected for pregnancies with both asthma and GDM, suggesting the presence of both conditions is associated with worse maternal and neonatal health.