Trends and Factors of the Twinning Rate: The Case of France during the Twentieth Century

Gilles Pison, Institut National d'Études Démographiques (INED)
Nadège Couvert, Institut National d'Études Démographiques (INED)

The proportion of deliveries which are twin deliveries has varied in France over the twentieth century. Close to 11 per 1,000 in 1900, it has first declined, reaching a low 8.9 per 1,000 in 1972. Then it has risen rapidly up to 15.0 per 1,000 in 2000, a 69% increase compared with 1972. The paper examines the roles played by different factors : changes in age at childbearing, diffusion of treatments against infertility, family planning. The effect of this last factor is examined more in detail through a study of the consequences of the arrival of twins on the size and composition of a family, and more specifically, the fertility after a twin delivery. Do women who delivered twins get less frequently pregnant subsequently than those who delivered single birth ? The study analyses 278 000 biographies of women representative of the French female population aged 15 years or more who were interviewed in 1999.