Background
Suspected appendicitis is a common non‐obstetric indication for emergency abdominal surgery during pregnancy.

Aims
Assess the risk of preterm birth and other maternal and neonatal adverse birth outcomes following appendicectomy during pregnancy.

Materials and Methods
Population‐based data linkage study of women with singleton births in New South Wales, Australia, 2002–2014. Pregnancies with appendicitis and appendicectomy were compared to pregnancies without appendicitis. Crude and adjusted hazard ratios (aHR) with 95% confidence intervals (CI) for preterm birth were estimated. Modified Poisson regression with robust variance was used to estimate crude and adjusted risk ratios (aRR) with 99% CI for other outcomes.

Results
Of 1 124 551 eligible pregnancies, 1024 (0.9/1000 pregnancies) had appendicitis and appendicectomy. Of these, 566 (55.3%) had laparoscopic and 458 (44.7%) had open appendicectomy. Appendicectomy at later gestational ages was associated with increasing rates of preterm birth. After adjustment for maternal and pregnancy factors, appendicectomy was associated with increased risk of preterm birth (overall aHR 1.73, 95% CI 1.42–2.09; planned aHR 2.08, 95% CI 1.60–2.72), maternal morbidity (aRR 2.68, 99% CI 1.88–3.83) and neonatal morbidity (aRR 1.42, 99% CI 1.03–1.94). However, there was no difference in perinatal mortality rates.

Conclusion
Appendicectomy during pregnancy is associated with increased risk of spontaneous and planned preterm birth, maternal and neonatal morbidity. Availability of resources to prevent or manage preterm labour should be considered when appendicectomy is performed at gestational ages of 20 weeks or more.