A new study finds that triplets and higher multiple births increasingly are the result of drugs given to women to make them produce eggs, not from using multiple embryos from IVF, or lab-dish fertilization.
More than one-third of twins and three-quarters of triplets-and-more births in the U.S. are due to fertility treatments.
Infertility usually is treated not with IVF but simpler measures such as drugs to spur the ovaries to make eggs. If doctors do not monitor how many eggs are produced, risky multiple births can result.
From 1998 to 2011, the proportion of twin births due to IVF increased. However, fertility drugs played a played a bigger role in the rate of triplet and higher multiple births.
Results are in Thursday's New England Journal of Medicine.