The occurrence of triplets is becoming rarer in the United States. Here's the reason behind it

The birth of triplets, quadruplets, and even higher multiples is steadily on the decline across the United States.

The incidence of triplet and higher-order births in the US dropped by 62% between 1998 and 2023, according to a report released by the US Centers for Disease Control and Prevention on Thursday. The most significant declines were observed among mothers aged 30 and older.

This drop in birth rates seems to be linked to tighter guidelines regarding the number of embryos transferred during assisted reproductive procedures like in vitro fertilization (IVF), according to researchers from the CDC’s National Center for Health Statistics.

Couples are more likely to conceive twins, triplets, or even higher-order multiples when using assisted reproductive technologies, as these treatments often involve transferring several embryos into the uterus in hopes of achieving a successful pregnancy.

Transferring multiple embryos not only increases the chances of a successful pregnancy but also raises the likelihood that the pregnancy could result in multiple fetuses – leading to twins, triplets, or more.

“Tracking trends in triplet and higher-order multiple births is crucial because women carrying triplet or more pregnancies face greater risks of complications, and their babies are more likely to experience preterm birth or infant mortality,” said Joyce Martin, a researcher at the National Center for Health Statistics and lead author of the report, in an email.

As fertility treatments became more widespread after the 1980s, there was a noticeable increase in multiple births, according to 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 introduced guidelines on the number of embryos to transfer in various situations, aiming to minimize the risks of complications, including preterm births, for women undergoing fertility treatments.

While the new data doesn't specify how many multiple births occurred naturally versus through assisted reproductive technologies (ART) like IVF, the overall decline seems to align with the introduction of the guidelines.

The guidelines were first introduced in 2004, according to Hill, and were updated in 2006, 2008, 2009, 2013, 2017, and 2021.

“If you examine the CDC's data, you can observe that these declines tend to follow updates to the guidelines, occurring every year or two,” Hill remarked.

“These guidelines have adapted as the technology has advanced,” he continued. “I believe they’ve been effective in making fertility treatments safer, which is ultimately the goal when addressing the issue of higher-order multiples.”

Part of the recommendations in the most recent guidelines, released in 2021, include advising the transfer of only one embryo for patients under 35, while for patients over 40, no more than four untested early-stage embryos are recommended.

The changes in recommendations regarding embryo transfers are not the only factors that may have contributed to the decrease in triplet and higher-order births in recent decades.

There has also been a shift in the use of fetal reduction during fertility treatments, a procedure aimed at reducing the number of fetuses when a pregnancy involves triplets or more, according to Dr. Amanda Williams, interim chief medical officer for the nonprofit March of Dimes, who was not involved in the NCHS data.

She also called the new NCHS report, which shows a decline in triplet and higher-order multiple births, “great news” for maternal and infant health.

“When carrying three or more babies, the risks are significantly higher for preterm birth, low birth weight, infant mortality, NICU stays, and for mothers, the increased likelihood of gestational diabetes, hypertension, and conditions like preeclampsia,” she explained. “This is positive news for families, as triplet and higher-order pregnancies pose much greater risks for both mothers and babies.”

A rising ‘public health concern’

In previous years, the rate of triplet and higher-order multiple births in the United States climbed from 37 out of every 100,000 births in 1980 to a record high of approximately 194 births per 100,000 in 1998, according to the latest report.

This “unprecedented increase” was linked to women having children at older ages and the growing use of fertility treatments, as noted by Martin and her co-author Michelle Osterman in the report.

“The surge was a public health concern due to the higher risk of negative maternal and infant health outcomes associated with triplet and higher-order births compared to twins and singletons,” they stated in the report.

However, since 1998, the rate of triplet and higher-order multiple births in the United States has fallen to around 74 out of every 100,000 births, according to the new data.

Between 1998 and 2009, the rates of triplet and higher-order births dropped slightly, by 21%, to approximately 154 per 100,000 births by 2009. The significant decline began between 2009 and 2023, when the rates fell by 52%, according to the latest report, which uses data from the CDC’s National Vital Statistics System. Many people may recall that 2009 was the year Nadya Suleman, famously known as 'Octomom', gave birth to eight babies following an IVF procedure.

The latest data also revealed that the number of triplet and higher-order births in the United States has decreased by 65% from 1998 to 2023. The number dropped from 7,625 births in 1998 to 6,340 in 2009, and then more sharply to just 2,653 births last year.

The new statistics “reflect what we’ve observed in fertility care practices,” said Dr. Asima Ahmad, an endocrinologist and fertility specialist who is also the chief medical officer and co-founder of Carrot Fertility, a company that assists employers with fertility benefits.

“Advancements in embryology labs have made it possible to grow embryos longer than before, and there’s more testing available to assess the health of embryos,” Ahmad, who was not involved in the NCHS report, shared in an email. “As a result, it’s becoming more common for doctors to transfer just one embryo at a time to increase the chances of a singleton pregnancy, which is the healthiest outcome for both the parent and the baby.”

When analyzing the data by maternal age, the study revealed significant declines in triplet and higher-order multiple birth rates between 1998 and last year. For mothers aged 20 to 24, the rate dropped by 16%, by 57% for mothers aged 25 to 29, 77% for those aged 30 to 34 and 35 to 39, and 67% for mothers aged 40 and older.

The researchers also discovered considerable racial disparities in the data.

For White mothers, the rate of triplet and higher-order multiple births decreased by 71% from 1998 to last year. Among Hispanic mothers, the decline was 25% from 1998 to 2023.

In contrast, for Black mothers, the rate of triplet and higher-order births increased by 21% from 1998 to 2009, with no significant change from 2009 to 2023, resulting in a 25% overall increase from 1998 to last year.

The most significant declines were observed among White women over 30, a group with the greatest access to in vitro fertilization and embryo transfers, where decisions to transfer fewer embryos could be influencing the outcomes, according to Williams from March of Dimes.

However, various forms of assisted reproductive technologies may be contributing to these racial disparities, she added.

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Williams pointed out that Black women and those from low-income backgrounds may lack access to the most advanced IVF technologies, which could affect their reproductive outcomes.

Instead, they might be relying on less advanced methods, such as using clomiphene with insemination to stimulate the ovaries and increase egg production, leading to higher rates of twins and triplets. Therefore, we should not equate all assisted reproductive technologies with IVF, as there are less invasive options that could be more commonly used by Black and low-income women.

Dr. Rachel McConnell, an assistant professor of obstetrics and gynecology at Columbia University’s Vagelos College of Physicians and Surgeons, who was not involved in the study, described the new data as 'extremely insightful' in an email.

She further emphasized that the report’s findings suggest that the American Society for Reproductive Medicine’s guidelines, which recommend limiting the number of embryos transferred, have played a role in decreasing the incidence of multiple pregnancies in IVF procedures.