1. The twinning rate in Europe and Africa;Bulmer;Ann Hum Genet,1960
2. Relative birthweights of twins;Friedman;Obstet Gynecol,1977
3. The fetus of multiple gestation;Guttmacher;Obstet Gynecol,1958
4. The twin delivery: factors affecting second twin mortality;Little;Obstet Gynaecol Survey,1958