Sex differences in birth defects: a study of opposite-sex twins.
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.
Cui
Wei
W
Division of Neonatology, Department of Pediatrics, College of Medicine, University of Florida, Gainesville, 32610-0296, USA. terrycui@yahoo.com
Ma
Chang-Xing
CX
Tang
Yiwei
Y
Chang
Vivian
V
Rao
P V
PV
Ariet
Mario
M
Resnick
Michael B
MB
Roth
Jeffrey
J
D000013:Congenital Abnormalities / Q000453:epidemiology* / Q000473:pathology; D005260:Female; D006801:Humans; D008297:Male; D012189:Retrospective Studies; D012307:Risk Factors; D012737:Sex Factors; D014427:Twins