Decrease in twinning rate in a hospital in Tokyo during World War II.

In order to investigate changes in twinning rate during World War II and postwar years, when the people in Tokyo suffered from malnutrition, about 80,000 delivery records during 1924-86 at one hospital in downtown Tokyo were examined. The twinning rate decreased from 1.47% in the 1920s to 0.81% in the 1980s. During the 1940s, the rate was 1.03% for 1940-42 and 0.94% for 1948-49, but it dropped down to 0.70% for 1943-47. In 1945, when Tokyo was heavily bombed repeatedly to be burnt out, and the people suffered from severe malnutrition, only one case of twinning was found among 305 maternities at this hospital (0.33%). While the mean birth weight of term singleton babies was 2953 g in 1940-41, it decreased to 2918 g in 1943-47, especially to 2856 g in 1945. This change in birth weight evidenced that the nutritional conditions in Tokyo became worse in 1943-47. This report suggests that the twinning rate decreased also during this period in Tokyo when the people suffered from malnutrition.