Objective To investigate the risk of adverse birth outcomes for women who underwent non-obstetric abdominal surgery during pregnancy compared with that of those who did not undergo surgery. Design Retrospective cohort study Setting Korea National Health Insurance (KNHI) claims database Population A total of 8,167 women who did non-obstetric surgery and 3,710,123 women who did not undergo surgery and in 2006-2016. Methods The two groups were compared using a multivariate Cox proportional hazard model. The primary outcome assessed was neonatal complications and secondary outcomes were obstetric complications. Main Results Multivariate Cox proportional hazards regression revealed that risk of preterm birth [hazard ratio (HR) 2.06, 95% confidence interval (CI) 1.86-2.29], low birth weight (LBW) (HR 1.65, 95% CI 1.49-1.82), C/S (HR 1.14, 95% CI 1.09-1.19), gestational hypertension (HR 1.36, 95% CI 1.19-1.56), and placenta previa (HR 1.57, 95% CI 1.33-1.87) was significantly higher in women who underwent non-obstetric surgery during pregnancy compared to women who did not undergo such surgery. When comparing the laparoscopic and laparotomy groups for risk of fetal outcomes, the risk of LBW was significantly decreased in laparoscopic adnexal resection during pregnancy compared to that of laparotomy (HR 0.62, 95% CI 0.40-0.95). Conclusion: Non-obstetric pelvic surgery during pregnancy was associated with higher risk of preterm birth, LBW, gestational hypertension, placenta previa, placental abruption, and C/S. Although the benefits and safety of laparoscopy during pregnancy appear similar to those of laparotomy in pregnancy outcomes, laparoscopic adnexal mass resection was associated with a lower risk of LBW.