Upped risks also exist for mothers of twins, Martin said, and include a higher odds for Cesarean delivery, gestational hypertension and diabetes, she said.
About 90 percent of twins are born via C-section, Martin noted.
Will American women continue to see an increase in twin births? "The pace of increase has declined somewhat in recent years," Martin said, "but it's too soon to say whether that trend will continue."
It's possible that, due to changes in infertility treatments, the twin birth rate may be slowing, Martin said. "As the baby boom generation ages out and reproductive therapies become more refined that might lessen the twin birth rat," she said.
Multiple births in Western Europe and other countries during the 1980s and 1990s have also increased, the authors note, and these are also associated with maternal age and infertility therapies.
This report deals only with twins, but the growth in the number of multiple births is even more "dramatic," and the outcomes are even more "problematic," Martin said.
Dr. George Attia, an associate professor of OB-GYN and director of the division of reproductive endocrinology and infertility at the University of Miami School of Medicine, said technology is helping to reduce the number of twin births.
"Twins and multiple births is one of the unwanted effects of fertility treatment," Attia said. "We are moving towards a single-embryo transfer to reduce the risk of multiple pregnancy," he said. "I am sure the rate will keep falling as technology improves."
Having fewer multiple births will also reduce the risks to infants and mothers, Attia agreed.
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