Body mass index and major surgical complications in outpatient surgical abortion: an Australia-wide case-control study

Existing evidence on the association between body mass index (BMI) and surgical abortion complications is inconclusive and derives exclusively from retrospective cohort studies conducted in the United States of America, often underpowered for uncommon surgical outcomes. In Australia, BMI is commonly considered when determining eligibility for outpatient surgical abortion, yet no Australian data have examined its association with major surgical complications.

We conducted a retrospective case-control study across 10 oupatient surgical abortion clinics operated by MSI Australia between 2016 and 2024. Cases were procedures complicated by major surgical complications (haemorrhage ≥500 mL, uterine perforation, hospital transfer, laparoscopy, laparotomy, disseminated intravascular coagulation, intensive care admission, blood transfusion, or hysterectomy), identified through mandatory incident reporting. Four gestation-matched controls were selected per case. BMI was analysed as a continuous variable, as obesity (≥30 kg/m2), and by ordered categories. Multivariable logistic regression adjusted for parity, gestational age and previous caesarean section.

BMI data were available for 775 of 795 individuals (159 cases, 636 controls). Mean BMI was slightly higher among cases than controls (25.9 vs 24.8 kg/m2; P = 0.017), but distributions were similar. Crude associations between BMI, obesity and complications did not persist after adjustment (per-unit increase: adjusted odds ratio (aOR) 1.01, 95% confidence interval [CI] 0.97-1.04; obesity: aOR 1.24, 95% CI 0.78-1.96).

BMI was not an independent predictor of major surgical complications in outpatient surgical abortion within the BMI range represented. Risk stratification should prioritise gestational age, parity and previous caesarean section rather than BMI alone, noting limited data for very high BMI categories.