National Toxicology Program

Since 1980, the incidence of multiple births has been increasing in the US. Two factors contributing to this increase are 1) a greater number of women over the age of 30 becoming pregnant (women over 30 are more likely to have multiples) and 2) an increase in the use of fertility-stimulating drugs and assisted reproductive techniques. Women carrying more than one baby are at increased risk of pregnancy complications.

• March of Dimes: Multiples: Twins, Triplets and Beyond