Triplets are becoming less common in the United States. Here’s why

(CNN) — Giving birth to triplets, quadruplets or even more has become increasingly less common in the United States.

The rate of triplet and higher-order births in the US declined 62% between 1998 and 2023, according to a report published Thursday by the US Centers for Disease Control and Prevention. And the largest declines in rates were seen among mothers 30 and older.

This decline appears to be associated with how guidance has strengthened around the number of embryos transferred during the use of assisted reproductive technologies like in vitro fertilization, known as IVF, wrote the researchers, from the CDC’s National Center for Health Statistics.

Couples are more likely to have twins, triplets or more babies in a single pregnancy when using assisted reproductive technology because these fertility treatments may involve transferring multiple embryos into the uterus in hopes of resulting in a pregnancy.

More embryos not only increase the likelihood of a viable pregnancy, they raise the risk that the pregnancy could involve more than one fetus – hence, twins, triplets or more.

“Monitoring trends in triplet and higher order multiple births is important because women with a triplet/+ pregnancy are at higher risk of complications during pregnancy and their infants are at greater risk of preterm birth and infant death,” Joyce Martin, a researcher at National Center for Health Statistics and the main author of the report, said in an email.

As fertility treatments became more mainstream after the 1980s, there was a rise in the incidence of multiple births, said Dr. Micah Hill, president of the Society for Assisted Reproductive Technology, who was not involved in the new report.

In the early 2000s, the American Society for Reproductive Medicine and the Society for Assisted Reproductive Technology started to issue guidelines on how many embryos should be transferred under different scenarios. The guidelines were issued to help reduce the risk of complications for women undergoing fertility treatments, including the risk of preterm birth.

While the new data does not indicate how many multiple births have been conceived spontaneously versus through assisted reproductive technologies (ART) like IVF, the overall decline does appear to parallel the introduction of the guidelines.

Guidelines were released in 2004, Hill said, and updated in 2006, 2008, 2009, 2013, 2017 and 2021.

“If you look at the CDC’s numbers, you can sort of see these declines follow every year or two after these guidance updates have happened,” Hill said.

“These guidelines have evolved as the technology has evolved,” he said. “I think it’s been successful in making fertility treatments safer, which is really what we care about when we’re talking about reducing these higher-order multiples.”

In part, recommendations in the latest guidelines, published in 2021, range from recommending the transfer of only a single embryo at a time for patients younger than 35 to recommending no more than four untested early-stage embryos for patients older than 40.

It’s not just guidance around embryo transfers that has changed in the past decades, possibly leading to declines in triplets and higher-order births.

There also have been shifts in the use of fetal reduction during fertility treatments, a procedure to reduce the number of fetuses when a pregnancy with triplets or more occurs, said Dr. Amanda Williams, interim chief medical officer for the maternal and infant health nonprofit March of Dimes, who was not involved in the NCHS data.

Separately, she called the new NCHS report, showing a decline in triplets and higher-order multiple births, “fantastic news” for maternal and infant health.

“When you have three or more babies inside, you are at a markedly increased risk for preterm birth, for low birth weight, for infant mortality, for NICU stays, and then on the maternal side, increased risk for gestational diabetes, increased risk for gestational hypertensive disorders like preeclampsia,” she said. “So this is good news for families, because triplets and higher order pregnancies are so much riskier for mom and baby.”

A growing ‘public health concern’

In previous years, the rate of triplet and higher-order multiple births in the United States rose from 37 out of every 100,000 births in 1980 to an all-time high of about 194 births per 100,000 in 1998, according to the new report.

This “unprecedented rise” was tied to women giving birth at older ages and “the increased use of fertility treatments,” Martin and her co-author Michelle Osterman wrote in the report.

“The increase was of public health concern because of the greater risk of adverse maternal and infant health outcomes of triplet and higher-order births compared with twins and singletons,” they wrote.

But since 1998, the rate of triplet and higher-order multiple births in the United States dropped to around 74 out of every 100,000 births last year, the new data showed.

Between 1998 and 2009, rates declined but not significantly, falling 21% to around 154 per 100,000 births in 2009. It was from 2009 to 2023 when rates dropped significantly, by 52%, according to the new report, which is based on birth certificate data from the CDC’s National Vital Statistics System. Many people might remember 2009 as the year when Nadya Suleman, known in the media as Octomom, delivered eight babies in a single birth after undergoing IVF.

The new data also showed that the raw number of triplet and higher-order multiple births in the United States declined 65% between 1998 and 2023 – falling from a total of 7,625 births in 1998 to 6,340 births in 2009 to, more sharply, 2,653 births last year.

The new data “are reflective of what we have seen in fertility care” on the ground, said Dr. Asima Ahmad, an endocrinologist and fertility expert who serves as chief medical officer and co-founder of Carrot Fertility, a company that helps employers set up fertility benefits.

“Embryology labs have advanced over the years, which allows them to grow the embryos out further than they used to be able to years ago. There is also additional testing available that can give more information about the health of the embryo,” Ahmad, who was not involved in the new NCHS report, said in an email. “Given these advances, it’s becoming more common for a physician to transfer one embryo at a time to achieve the goal of a singleton pregnancy – the healthiest option for the pregnant person and the baby.”

When looking at the data by maternal age, the researchers found that from 1998 to last year, triplet and higher-order multiple birth rates declined 16% for mothers ages 20 to 24; 57% for mothers ages 25 to 29; 77% for mothers ages 30 to 34 and ages 35 to 39; and 67% for mothers 40 and older.

The researchers also found significant racial disparities.

Among White mothers, the triplet and higher-order multiple birth rate fell 71% from 1998 to last year. Triplet and higher-order births for Hispanic mothers fell 25% from 1998 to 2023.

However, the triplet and higher-order birth rate for Black mothers followed a different trend, climbing 21% from 1998 to 2009 and then not changing significantly from 2009 to 2023, resulting in an overall increase of 25% from 1998 to last year.

“The biggest drops were with White women over 30, and that is the group that would have the highest access to in vitro fertilization and actual transfer of embryos, where one could be making the decision to transfer fewer embryos,” March of Dimes’ Williams said.

But there are many other types of assisted reproductive technology, which could be factors driving these racial disparities, she said.

“When you think about Black women or you think about low-income women, they may not have access to the highest level of technology and IVF for their assisted reproductive technology,” Williams said.

“They may be using less technologically advanced means of assisted reproductive technology – such as clomiphene with insemination, where you’re going to be stimulating the ovaries to produce more eggs, therefore driving your numbers of twins and triplets,” she said. “So we can’t conflate assisted reproductive technology with IVF. There are less invasive, less technologically advanced forms of assisted reproductive technology that may be the ones that are being used by Black mothers and low-income mothers.”

Overall, the new data was “very informative,” Dr. Rachel McConnell, assistant professor of obstetrics and gynecology at Columbia University’s Vagelos College of Physicians and Surgeons, who was not involved in the report, said in an email.

She added that the report’s findings indicate that the guidelines set by the American Society for Reproductive Medicine to transfer a low number of embryos “has helped to reduce the number of multiple pregnancies” in IVF cycles.

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