Biological aspects of twin pregnancy in Dundee

A review is presented of 712 twin pregnancies which occurred in Dundee between 1956 and 1971. It shows a falling age of twin reproduction, a changing ratio of mono- to dizygosity and the poor growth rates of both types. Birth weight variations suggest that "crowding" in the uterus may affect the individual growth of each twin, but the combined weight of twins continues to increase to term and shows no obvious sign of restriction.