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Sex differences in birth defects: a study of opposite-sex twins
Wei Cui1, Chang-Xing Ma, Yiwei Tang
1Division of Neonatology, Department of Pediatrics, College of Medicine, University of Florida, Gainesville, 32610-0296, USA. terrycui@yahoo.com
Background:
Sex differences in structural birth defects are often confounded by environmental risk factors. Opposite-sex twins provide a unique model for detecting sex differences in birth defects while maximally controlling environmental risk factors in a natural setting.
Methods:
Population data from the Florida Birth Defects Registry were analyzed. A total of 4,768 pairs of twins who were discordant for sex and born between 1996 and 2001 were analyzed. The McNemar test was used to compare the differences between a male twin and his twin sister for the risk of developing specific defects and organ-system defects.
Results:
Of 4,768 twin pairs, 225 males (4.72%) and 175 females (3.67%) had birth defects. Among opposite-sex twin pairs, males had a 29% higher risk for birth defects than their twin sisters. Compared to their twin sisters, males had a 5.4 times higher risk for pyloric stenosis and a 2.4 times higher risk for obstructive genitourinary defect, but only one-tenth the risk for congenital hip dislocation.
Conclusions:
Sex differences in birth defects exist between opposite-sex twins.
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