Major Variation in the Incidence of Appendicitis Before, During and After Pregnancy: A Population-Based Cohort Study

Previous studies indicate a low incidence of appendicitis in third-trimester pregnancy, suggesting a protecting effect of pregnancy. This large population-based cohort study analyzes the association of appendicitis with pregnancy in more detail. The aim of the study was to investigate the incidence of appendicitis and negative appendectomy before, during and after pregnancy.

Cross-linking between two Swedish health registries provided data on appendectomy for all women in Sweden giving birth between 1973 and 2013. We analyzed the incidence rates (IR) of perforated and non-perforated appendicitis and negative appendectomy before, during and after pregnancy, and secular trends during the study period. Standardized incidence ratios (SIR) were estimated using age-, sex- and period-specific IR from the background population in Sweden.

Some 3,888,452 pregnancies resulted in birth during the study period. An appendectomy was registered for 27,575 women in the interval starting one year before and ending two years after pregnancy. The incidence of appendicitis varied substantially during and after pregnancy. SIR for perforated appendicitis was 0.47 (95% CI 0.38-0.59) in the third trimester, 3.89 (2.92-5.18) peripartum, 2.20 (1.89-2.55) in the puerperium and 1.27 (1.19-1.36) in the year postpartum. The pattern was similar for non-perforated appendicitis. Negative appendectomy decreased postpartum. Incidence rate of non-perforated appendicitis and negative appendectomy decreased for both pregnant and non-pregnant women during the study period.

The findings in this study suggest a protecting effect of pregnancy on the development of appendicitis, which is followed by a rebound effect after birth.