Unidentified multiple congenital abnormalities in twins. A population-based Hungarian study.

Of 1038 index patients with multiple congenital abnormalities, 34 were twins. This 3.3 per cent is higher than the Hungarian birth rate of about 2.1 per cent. However, after the exclusion of cases with congenital abnormality association of low birth weight newborn infants and with genital anomalies of the male, the twin birth rate was 1.8 per cent. Thus, the unidentified multiple congenital abnormalities have no common cause with twinning.