Sex differences in the prevalence of human birth defects: A population-based study

Background: Sex differences in the prevalence of several human birth defect s have often been reported in the literature, but the extent of sex differe nces for most birth defects is unknown. To determine the full extent of sex differences in birth defects in a population, we examined population-based data from the Metropolitan Atlanta Congenital Defects Program (MACDP). Methods: MACDP records were analyzed for 1968 through 1995. We determined t he sex-specific prevalence of all major birth defects, using the total numb er of live births by sex during these years as the denominator. For each sp ecific defect, we calculated a relative risk with regard to sex on the basi s of the ratio of prevalence among males to prevalence among females. Male- female relative risks were also determined for total major birth defects an d for several broad categories of defects. Results: The overall prevalence of major defects at birth was 3.9% among ma les and 2.8% among females. All but two of the major categories of birth de fects (nervous system defects and endocrine system defects) had a higher pr evalence among males. Defects of the sex organs were eight and one-half tim es more prevalent among males and accounted for about half of the increased risk of birth defects among males relative to females. Urinary tract defec ts were 62% more prevalent among males, and gastrointestinal tract defects were 55% more prevalent among males. Among specific defect types, twofold o r greater differences in prevalence by sex were common. Conclusions: Our data indicate that sex differences in the prevalence of sp ecific human birth defects are common, and male infants are at greater risk for birth defects than female infants. Several mechanisms have been propos ed to account for these differences. Published 2001 Wiley-Liss, Inc.(dagger )