Projections of population-based twinning rates through the year 2100

OBJECTIVE: To present the first compilation of population-based twinning ra tes published after the year 1990 and to project population-based twinning rates through the year 2100. STUDY DESIGN: We searched the Internet-based MEDLINE database for articles published after 1990 in which population-based twinning rates were describe d. We used population-based data from national statistical authorities from Australia, Austria, Canada, Finland, Hong Kong, Israel, Japan, Norway, Sin gapore and Sweden, published by Y. Imaizumi in a recent article. U.S. figur es were based on data from the National Center for Health Statistics. Annua l growth rates of twinning were calculated and graphed, making the assumpti on that these rates would remain constant throughout the next century. RESULTS: Our report presents the most recent population-based twinning rate s. CONCLUSION: We strongly suggest that physicians reexamine their patterns of prescribing ovulation-inducing agents, which carry a greatly increased ris k of multiple pregnancy.