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Association of secondary sex ratio with smoking and parity.

Beratis NG, Asimacopoulou A, Varvarigou A

Department of Pediatrics, General University Hospital of Patras, University of Patras Medical School, Rio, Patras, Greece. nic-bera@med.upatras.gr

OBJECTIVE: To assess the sex ratio in offspring of smoking and nonsmoking mothers in relationship to parity. DESIGN: Prospective study. SETTING: University hospital. PATIENT(S): The authors studied 2,108 term singleton neonates born between 1993 and 2002, 665 from smoking mothers and 1,443 from nonsmoking mothers. INTERVENTION(S): A prospective recording of maternal age, parity and smoking status, and gender of neonates delivered over a 10-year period. MAIN OUTCOME MEASURE(S): Secondary sex ratio in regard to maternal smoking and parity. RESULT(S): The offspring sex ratio in the total sample studied was 1.09; in the offspring of smoking and nonsmoking mothers, it was 1.26 and 1.03, respectively, a statistically significant difference. In the offspring of smoking women who had parity 1, 2, and >or=3, it was 1.47, 1.35, and 0.92, whereas in those of nonsmoking women, it was 1.04, 1.00, and 1.03, respectively (the differences of the parity 1 and 2 groups between the offspring of smoking and nonsmoking mothers were statistically significant). Logistic regression analysis showed that the possibility of a boy being delivered by a mother who smoked was significantly greater in primiparous women than in women who had parity >or=3, independent of the maternal age. Conversely, parity did not affect significantly the sex ratio in the offspring of nonsmoking women. CONCLUSION(S): The findings suggest that among women who smoked, significantly more male than female offspring are born from primiparous women, whereas women who had parity >or=3 gave birth to more female offspring; biparous women give birth to significantly more male offspring, but the offspring sex ratio declined with the number of cigarettes when the mothers smoked >or=10 cigarettes per day.

Published 11 March 2008 in Fertil Steril, 89(3): 662-7.
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