Projections of population-based twinning rates through the year 2100

To present the first compilation of population-based twinning rates published after the year 1990 and to project population-based twinning rates through the year 2100.

We searched the Internet-based MEDLINE database for articles published after 1990 in which population-based twinning rates were described. We used population-based data from national statistical authorities from Australia, Austria, Canada, Finland, Hong Kong, Israel, Japan, Norway, Singapore and Sweden, published by Y. Imaizumi in a recent article. U.S. figures were based on data from the National Center for Health Statistics. Annual growth rates of twinning were calculated and graphed, making the assumption that these rates would remain constant throughout the next century.

Our report presents the most recent population-based twinning rates. When projected through the year 2015, twinning rates reach figures that could best be described as derived from a Jules Verne novel: Sweden, in this model, would have four times more twin than singleton births.

We strongly suggest that physicians reexamine their patterns of prescribing ovulation-inducing agents, which carry a greatly increased risk of multiple pregnancy.