Birthrate trends show fewer triplets, more twins in U.S.
Triplet births are at their lowest level in 18 years, while the number of twins born has been on the rise.
In 2013, there were 131,269 twin births, 4,598 triplet births, 276 quadruplet births and only 45 births that involved five babies or more.
CDC documents covering a period from 1990 to 2012 show a steep rise in twin births and the recent decline in births of triplets or more.
This trend is probably due to advances in assisted reproductive technology (ART), said Wildey. ART has been used since 1981 to help women become pregnant.
In the past, specialists in in vitro fertilization (IVF), a type of ART, would implant as many embryos as possible in hopes that at least one would survive and grow, he said.
The success rate of implanting two embryos “is so much better now,” Wildey said.
ART is being used more and has become increasingly effective, the CDC reports.
The number of treatments has risen from 55,002 in 1997 to 176,247 in 2012.
In 1997, 39.9 percent of egg transfers resulted in a live birth; by 2012, that had risen to 56.4 percent.
The ART technology “is definitely improving, especially in the last five or six years,” said Dr. Stephanie Dahl, reproductive endocrinologist with Sanford Health in Fargo.
Because of these improvements, the American Society of Reproductive Medicine issued strict guidelines in 2008 to encourage doctors and patients to transfer fewer embryos using IVF, she said.
The ASRM recommended that “no more than two embryos be implanted for patients under the age of 35 with a favorable prognosis” and that consideration be given to transferring just one, Dahl said.
“The major concern is complications during the pregnancy, including gestational diabetes, hypertension and pre-term labor,” she said.
In the past, when IVF success rates were lower, “it was routine to implant two and sometimes three” embryos in the quest for a successful pregnancy, she said.
In those days, three or more embryos were sometimes transferred, especially in women who were over the age of 40 or who had failed multiple IVF cycles, she said. “Now, for most patients, we usually transfer one or two embryos.”
For women who, for medical or other reasons, can’t risk having multiple babies, she recommends transferring one embryo, she said.
Dahl and other specialists in her field “are using less of the fertility drugs” than in the past, she said. “Using IVF, we have a better chance of success with fewer embryos.”
Among women younger than 35 who underwent ART at Sanford’s Reproductive Medicine Clinic, 2012 data shows that 71 percent had a positive pregnancy and 56 percent of those continued on under the care of an obstetrician-gynecologist, Dahl said.
“That percentage is much higher than when I started practicing in this field seven years ago.”
Even following the ASRM guidelines, twins are a common outcome, she said.
“In 2012, 29 percent of IVF patients at our center under the age of 35 delivered twins,” Dahl said. “There were no triplets.”
The statistics that show a rise in the twin birthrate “may be partially due to an increased number of women seeking infertility treatments that don’t involve IVF such as clomid, femara and fertility drugs that lead to the ovary releasing more than one egg each menstrual cycle,” she said.
“These methods of helping women conceive are much more common than IVF, which is usually the option when all other methods of treatment have failed,” she said.
“Our goal is to help families achieve a healthy pregnancy with a healthy baby.”
Women who are using ART are much older, according to the CDC.
The tendency to delay pregnancy “is a trend that you see,” Wildey said. The results of that decision are twofold: “They end up needing assisted reproductive technology or they are at risk for multiple births.”
The choice to delay or not “is a matter of give and take,” he said.
Even without treatments, older women are naturally more likely to have a multiple birth because they are more prone to producing multiple eggs in a cycle, he said.
So part of the reason why twins are on the rise is because women are having children at a later age.
The CDC reports that about one-third of the rise in twins is due to those natural factors — the rest attributed to the growing use and effectiveness of ART.