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esi Fortin is an increasingly rare type of mother: a mother of triplets.

After a steep rise in the 1980s and ’90s, the number of women giving birth to three or more babies is about half of what it was at its peak. The reason, scientists say, for both the rise and the fall of these multiple births is changing practices in assisted reproduction.

Fortin, 30, gave birth to identical boys and a girl in August 2015 after struggling for years with infertility. When she and her husband decided to have in vitro fertilization, they chose to implant two embryos in hopes of having at least one baby.

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Just two decades ago, a woman Fortin’s age would commonly have had twice as many embryos implanted. “The reason [doctors] put in many embryos is that we weren’t sure which were the good ones,” said Dr. Lawrence Grunfeld, associate clinical professor of obstetrics, gynecology, and reproductive science at Mount Sinai Hospital.

But, probably partly thanks to improvements in IVF, both of Fortin’s embryos implanted — and one divided to form identical twins.

Data released Thursday by the US Centers for Disease Control and Prevention show that the rate of triplet and higher-order births dropped 60 percent for women over the age of 25 from 1998 to 2014. The biggest decline was in women 45 and older, where the rate of these births is just a third of what it once was. The rates did not change significantly for women under the age of 25.

That curve mirrors a trend in reproductive technology. The rise in higher-order multiples peaked in 1998 when implanting four or more embryos was a common practice. As various parts of IVF improved through the latter part of the 20th century, these implantation rates were increasingly driving multiple births.

Vitrification, or flash freezing, began allowing doctors to freeze and thaw embryos at a survival rate of nearly 100 percent. This meant all the embryos do not need to be used at once. Doctors also developed better means of screening embryos before they were implanted, what’s called preimplantation genetic screening. “We have learned that most embryos that don’t stick, don’t stick because the embryos themselves were not normal,” said Grunfeld.

As a result, in 1998 the American Society for Reproductive Medicine (ASRM) and the Society for Assisted Reproductive Technology (SART) introduced guidelines to encourage doctors to implant fewer embryos, and those have been continually revised downward since then. On top of that, doctors have felt a professional pressure to be conservative in their practice. “Even staying within the guidelines there is a concern about multiple birth … so there has been an incredibly big push over the past two or three years to put in only one embryo at a time,” said Grunfeld.

The drop in triplets, quadruplets, and others is welcomed by doctors. Pregnancies of multiple babies have an increased risk of complications. According to ASRM and SART, the goal of assisted reproduction is to achieve a singleton birth.

“Infants born in triplet deliveries are at high risk of poor outcomes,” said Joyce A. Martin, the lead author of the CDC’s new analysis. “So a decline in these deliveries is a positive for infant health overall and for public health overall.”

It is possible to reduce the number of fetuses in a multifetal pregnancy, but the procedure has some risks and may carry significant psychological consequences for families struggling with infertility.

Guidelines based on the patient’s age and health history help doctors and their patients decide exactly how many embryos to implant. No more than five embryos may ever be implanted at a time, and facilities that consistently have higher-order births may be audited by SART.

“We all know the story of the ‘Octomom’ where the physician actually adhered to a patient’s request to put in eight embryos and she got the eight babies,” said Grunfeld. “That was considered medical malpractice.”

The guidelines stipulate that healthy patients under the age of 35 should be offered a single-embryo transfer and no more than two embryos. If the patient elects to transfer two embryos, they must be counseled on the risk of a multifetal pregnancy.

This is what happened to Desi and her husband, Ryan Fortin, when they decided to implant two embryos. Their physician encouraged them to implant one embryo, but after two years of trying to conceive, “we had a hard time doing one because we were worried that it was not going to take. After going through what we went through emotionally and my body physically, it would have been devastating just putting one embryo back and having it not take.”

Fortin Triplets
Desi and Ryan Fortin with their triplets in December 2015. Courtesy Desi Fortin

In the course of blogging about her experience with infertility, Desi found a community that shared their experiences with IVF. Some families she knew transferred two embryos and got one baby, others got two, others implanted one and got none, she said.

Both of Desi’s embryos successfully implanted. During her first ultrasound, she and Ryan discovered that one of the embryos had split and they were expecting triplets. At 34 weeks she delivered Charlize and her younger twin brothers Sawyer and Jax by caesarean section.

Still, even knowing her one baby might turn into three, Desi said that she would make the same decision again today. “You need to take in what the doctors are telling you, take in the advice and listen, and just go with what is best for you,” she said.

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