Perinatal risk factors for future SLE: a population-based nested case-control study.

OBJECTIVE: To investigate the association between perinatal characteristics and the offspring's risk of lupus using population-based registers in Sweden.

METHODS: We conducted a nested case-control study, identifying systemic lupus erythematosus (SLE) cases from the National Patient Register and controls sampled from the general population matched on birth year, sex, and residential county. We obtained data on the mother's health and age during pregnancy and characteristics of labor and delivery from the Medical Birth Register (births from 1973 through 2008) for cases and controls. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using conditional logistic regression models overall and separately for males and females.

RESULTS: We identified 774 cases and 3337 controls. Age at which SLE was first observed ranged from 0 to 36 years old. High birth weight was not a risk factor for SLE and did not differ by sex. Males had a 2.4-fold increased odds of SLE if born preterm (<37 weeks; OR = 2.41; 95% CI 1.09, 5.36). Birth order was significantly associated with SLE, particularly among females (first born vs. not OR = 0.77, 95% CI 0.64, 0.94; continuous birth order OR = 1.12. 95% CI 1.02, 1.24).

CONCLUSION: Being born first was associated with reduced odds of SLE and the odds of SLE increased by 12% for every additional birth. Preterm birth was associated with increased odds in males only. Unlike previous work, high birth weight was not a risk factor for SLE.