SCIENCE FILE / An exploration of issues and trends affecting science, medicine and the environment

Q: How often are triplets, quadruplets and quintuplets born?

A: The number of multiple births in the United States is increasing dramatically, primarily as the result of increased use of in-vitro fertilization techniques. In the past 20 years, the number of triplets born each year has more than doubled, to 2,500 sets, while the number of quadruplets has more than tripled, to about 225 sets per year, according to the Grolier Encyclopedia. About 50 sets of five or more babies are born each year. Although the risk of death for multiple-birth infants is 15 times that for single ones, the vast majority do survive.