BACKGROUND: Pregnancy, delivery, and the postpartum period may imply morbidity leading to work incapacity; however, this is seldom studied. This study aimed to compare twin sisters giving or not giving birth regarding occurrence of sickness absence (SA) and disability pension (DP).

METHODS: This population-based cohort study included all 6323 female twins born in Sweden 1959-1990, using register data for 1994-2010 about SA and DP. Average number of SA/DP days/year was calculated in relation to the year of the first delivery, or, if not giving birth, the year when the twin sister gave birth. Twin pairs discordant for delivery were used to investigate the importance of genetic and environmental factors for occurrence of SA and DP.

RESULTS: In all, 52% had a first delivery during 1994-2010. Except for the year of delivery, the average number of SA days/year was similar when comparing women who gave birth to those who did not, while number of DP days was significantly higher in women who did not give birth. Differences between the groups seem attributable to genetic factors. Women who delivered once had higher levels of SA and DP than those who had several deliveries. DP with mental diagnoses was more common among women who had not delivered whereas DP with musculoskeletal diagnoses occurred more often among women who delivered.

CONCLUSIONS: Levels of SA were similar among women who gave birth and who did not. Women not giving birth had significantly higher levels of DP, indicating health selections into childbirth.