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. 2005 Nov;73(11):876-80.
doi: 10.1002/bdra.20196.

Sex differences in birth defects: a study of opposite-sex twins

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Sex differences in birth defects: a study of opposite-sex twins

Wei Cui et al. Birth Defects Res A Clin Mol Teratol. 2005 Nov.

Abstract

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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