To determine whether the sex ratio among offspring born to women with systemic lupus erythematosus (SLE) or rheumatoid arthritis (RA) is different from that in the general population.
Women with a singleton delivery were identified from the Swedish Medical Birth Register (1973-2012) and linked to the National Patient Register (1964-2012) to identify those with prevalent SLE or RA. A sample of general population comparators was identified from the Swedish Total Population Register. We calculated the percentages of males born to women with SLE, women with RA, and women in the general population, as well as the risk ratio (RR) for having a male child among first births and all births. We also examined a history of antiphospholipid syndrome in the SLE population, using International Classification of Disease codes before or at delivery.
We identified 661 women with SLE and 1,136 women with RA before their first delivery. There were a total of 1,401 deliveries to women with SLE and a total of 2,674 deliveries to women with RA. Compared with women in the general population, women with SLE and those with RA had a lower risk of having a first-born male (RR 0.92 [95% confidence interval 0.85-1.00] and RR 0.93 [95% confidence interval 0.87-0.99], respectively). Among all births, the percentage of male offspring remained lower than that in the general population, but the difference was not statistically significant for RA.
The proportion of male offspring born to women with prevalent SLE or RA at delivery was lower than that in the general population, although the difference was small. Chronic inflammation may affect the sex ratio through fetal loss in early gestation.