Fetal deaths with birth defects among Japanese multiples, 1974.

Source of data is "Survey on Socio-Economic Aspects of Vital Events-Plural Births in 1975", including 12,392 twin pairs, 124 triplet sets, 7 quadruplet sets and 1 quintuplet set. Fetal deaths were 3,285 for twins, 141 for triplets, 17 for quadruplets, and 5 for quintuplets, among which the number of birth defects were 78, 3, 0, and 0 respectively. Concordant twin pairs with the same category of birth defect were 20 among 56 pairs (0.36). As for the remaining 36 pairs, 2 pairs had different category of birth defects, 27 pairs had liveborn cotwins, and 7 pairs were both fetal deaths among which a twin had birth defect. The second-born twins had birth defects more frequently than the first-born twins among fetal deaths (28 vs 6).