Systemic sclerosis, birth order and parity

Aim A recent study identified increasing birth order to be a risk factor for the development of systemic sclerosis ( SS c). This finding supports the theory that transplacental microchimerism may be a key pathological event in the initiation of SS c. We investigated the relationship between birth order and parity and the age of onset of SS c in S outh A ustralia. Method A retrospective analysis of patient data in the S outh A ustralian Scleroderma Register was performed. Data were obtained from a mailed questionnaire. Control data was collected prospectively using a similar questionnaire. The relationship between birth order, family size or parity and risk of subsequent development of SS c was analyzed by mixed effects logistic regression analysis. Results Three hundred and eighty‐seven index probands were identified and compared with 457 controls. Controls were well matched for gender, but not for age. No statistically significant relationship was identified between SS c and birth order, parity in females, family size, age at first pregnancy in females or gender of first child in parous females. Conclusion Our data suggests that parity, age at first pregnancy and the gender of the first child are not relevant factors in our understanding of the epidemiology and pathogenesis of SS c. Birth order and family size in both genders also appears irrelevant. These results argue against microchimerism as being relevant in the pathogenesis of SS c and add further support to the theory that stochastic events may be important in the etiopathogenesis of SS c.