Background/Purpose: One’s own fetal environment has been linked to future heart disease, breast cancer, and rheumatoid arthritis. Prior work showed that among older women in the US, high birthweight and preterm birth were associated with an increased risk of SLE. Risk factors were self-reported in relatively crude categories, and data were limited on other factors of interest and unavailable for younger individuals or males. In systemic sclerosis and lupus, some have investigated links between birth order and future disease. Therefore we used population-based registers to study the association between perinatal factors and lupus in the Swedish population born 1973 onwards.

Methods: Cases were identified in the National Patient Register with at least two visits with an SLE-specific discharge diagnosis (using ICD codes) and at least one SLE-discharge from a specialty department. General population controls were matched (5:1) on birth year, sex, and residential county when the case was first identified. Using the Medical Birth Register, we obtained data on the case’s mother’s health and age during pregnancy and characteristics of labor and delivery. Restricting our study population to singleton births yielded 774 cases and 3337 controls. Birthweight was reported in grams and categorized according to standard definitions. Preterm birth was defined using gestational age in weeks and categorized. Parity was included as a continuous variable and an indicator for first born. Odds ratios and 95% CIs were estimated using conditional logistic regression models. Analyses were conducted for the entire population and separately for males and females. In sensitivity analysis, birthweight and preterm status were redefined using similar definitions to previous studies.

Results: High birthweight was not a risk factor for SLE in this younger population. Results were generally similar by sex. Preterm birth (<37 weeks) was not significantly associated with future risk of SLE overall, nor when very preterm was considered separately. Recategorizing these variables as they had been analyzed in the Nurses’ Health Studies did not appreciably change the results, nor did adjustment for maternal age, smoking in early pregnancy, and maternal BMI. Being first born was associated with 20% lower odds of SLE- this was driven by the association in females (OR=0.77, 95% CI=(0.64, 0.94)). Similarly parity was associated with SLE (OR=1.12, 95% CI=(1.02, 1.23)).

Conclusion: Lower parity and being born first were associated with reduced odds of SLE. Unlike previous work, high birthweight did not appear to be a risk factor, however this may be consistent with birth cohort trends when we examined previous published works.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/perinatal-risk-factors-for-systemic-lupus-a-register-based-case-control-study/