Giving birth to triplets, quadruplets or even more has become increasingly less common in the United States, the decline being particularly noticeable in mothers 30 and over, according to a recent report.
The publication, released last week by the US Centres for Disease Control & Prevention, (CDC) shows that the rate of triplet and higher-order births in the country dropped by 62% between 1998 and 2023, reports CNN.
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 fertilisation (IVF), wrote the researchers, from the CDC’s National Centre 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 foetus – 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,” said Joyce Martin, a researcher at National Centre for Health Statistics and the main author of the report.
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 do 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,” he added.
“The guidelines have evolved as the technology has evolved. 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 over 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 foetal reduction during fertility treatments, a procedure to reduce the number of foetuses when a pregnancy with triplets or more occurs, said Dr Amanda Williams, interim chief medical officer for the maternal and infant health non-profit 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 are carrying three or more babies, 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 US 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.”
But since 1998, the rate of triplet and higher-order multiple births in the country dropped to around 74 out of every 100 000 births last year, the new data showed.
The authors also said the raw number of triplet and higher-order multiple births in the US 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.
“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.”
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 fertilisation and actual transfer of embryos, and making the decision to transfer fewer embryos,” March of Dimes’ Williams said.
triplets report in the US
Guidelines to the limit of embyros (Open access)
CNN article – Triplets are becoming less common in the United States. Here’s why (Open access)
See more from MedicalBrief archives:
Greater CVD risk for children conceived through IVF
‘Remarkable’ decline in global births — report
Heart defect risk for babies conceived through IVF – Swedish study
Plunging global fertility rates will lead to big world divide