Sex ratio and associated risk factors for 50 congenital anomaly types: clues for causal heterogeneity.

BACKGROUND: Sex ratio (SR) deviations have been reported for many congenital anomalies, but so far no satisfactory explanation for these deviations has been found. The aim of this study was to detect sex-related differences in the association between risk factors and congenital anomalies, and to relate these differences with possibly underlying causes of birth defects.
METHODS: Between 1982 and 1999, 1,444,646 newborn infants were examined by the Estudio Colaborativo Latino Americano de Malformaciones Congénitas (ECLAMC) network of South American maternity hospitals. Male relative risks were established for 39,425 infants with 50 selected single anomalies. Associations between male sex and risk factors were identified in nonmalformed infants. In malformed infants, sex-related risk differences were established, and the SR of these infants, with and without associated risk factors, were compared.
RESULTS: Infants with neural tube defects (NTDs) and intrauterine growth restriction had a lower SR than those with normal growth, while spina bifida without hydrocephaly (SB[sHy]) was the only NTD subtype without a significant female predominance. Multigravidity lowered the SR of SB(sHy) and HPP (HPP) cases. Increased paternal age inverted the SR of cleft lip (CL) with or without cleft palate (CL[P]) cases from male to female.
CONCLUSIONS: The results indicate etiological differences between high and low SB, a stronger relationship between multigravidity and female sex of the offspring than between multigravidity and a specific congenital anomaly, and a possible involvement of dominant mutations for CL(P), as suggested by the association with increased paternal age. Copyright 2003 Wiley-Liss, Inc.