Laterality patterns in infants with external birth defects

The lateral distribution of external birth defects has not been reported in a comprehensive way, and patterns in this distribution have not been exami ned. This study presents the lateral distribution of 6,390 unilateral defec ts from among 102 defect categories in data collected by the Metropolitan A tlanta Congenital Defects Program. Among all defects, 49% (95% CI 48-51%) w ere right-sided. Among mates and females, 51% (95% Ct 50-53%) and 47% (95% CI 46-49%) of the defects, respectively, were right-sided. Of the 102 defec t types, 57 had an excess of defects on the right side of the body; 39 had an excess of defects on the left side; and 6 were equally distributed. The excess on the right side was statistically significant for inguinal hernia, incarcerated inguinal hernia, microtia, preauricular sinus, talipes calcan eovalgus, and lambdoidal craniosynostosis. For the left side, the excess wa s statistically significant for preauricular tags, cleft lip, fused lip and cleft gum, cleft tip with cleft palate, congenital hip dysplasia, unstable hip, absent forearm or hand, anomaly of the knee, and skin tags. The perce ntage of right-sided defects among case subjects with unilateral defects wa s correlated with the percentage of mates among all case subjects (r = 0.24 , P < 0.05). Among male case subjects with unilateral defects, the correlat ion coefficient was 0.31 (P < 0.01), and among females with unilateral defe cts, it was 0.11 (P > 0.10). Differences in the lateral distribution of spe cific birth defects may be due to subtle differences in morphogenesis on th e left and right sides of the embryo brought about by establishment of left -right asymmetry prior to organogenesis. The fact that more defect categori es were right-sided than left-sided may be related to the observation that mitochondrial maturation in rat embryos is delayed on the right side. The r ight side, therefore, may be more susceptible than the left to defects caus ed by prenatal hypoxia. The significant correlation between the percentage right-sided and percentage male may then also be related to the observation that male sex hormones lower the mitochondrial respiration rate in rats an d increase rat sensitivity to chemical hypoxia. Investigators should consid er reporting the laterality of specific defects in both laboratory and epid emiological studies of birth defects. Right and left-sided defects should p erhaps be considered separately in etiologic studies of birth defects. Publ ished 1999 Wiley-Liss,Inc.(dagger).