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Premature births in the U.S. have increased over the past decade, but the reasons remain unclear. mkl/Getty Images
  • A recent CDC report shows that preterm birth rates in the U.S. have risen 12% in the past decade, but the reasons are unclear.
  • New research suggests that phthalates, also known as “everywhere chemicals,” may be contributing to the increase in premature births.
  • Experts suggest myriad factors may play a role, including pregnancy at a later age and chronic health conditions like obesity.
  • Abortion bans and racial disparities may factor into premature birth rates, particularly where access to quality prenatal care is limited.

Premature birth rates are rising in the United States, but the reasons are unclear and multifactorial.

Phthalates — also known as “everywhere chemicals” — have been tied to various health issues, including obesity, cancer, and fertility problems. Exposure to these hormone-disrupting chemicals can also impact how the placenta functions.

A new study examined the impact of chemicals in plastic containers and cosmetics on pregnancy and preterm births.

The results, published February 6 in The Lancet Planetary Health, show that phthalates may affect pregnancy outcomes.

In 2018, nearly 56,600 preterm births in the U.S. may have been linked to daily exposure to phthalates used to make plastic food containers and various cosmetics.

The study authors note that medical costs associated with these preterm births were expected to go as high as $8.1 billion over the course of the children’s lives.

As preterm birth rates continue to surge in the U.S. for numerous reasons, more research is needed to understand the impact of “everywhere chemicals” on pregnancy outcomes and other factors driving the increase.

A recent report from the Centers for Disease Control and Prevention (CDC) shows that preterm birth rates in the U.S. have increased over the past decade.

The National Vital Statistics Report details changes in the gestational age of newborn births that occurred at pre-term and early-term from 2014 to 2022.

During those 8 years, the percentages of preterm and early-term births rose by 12% and 20%, respectively. The percentage of full-term births declined by 6%, and late- and post-term births declined by 28%.

While there was fluctuation among preterm, full-term, and late- and post-term birth rates throughout the pandemic between 2020 and 2022, the increase in preterm births continued.

“This important information demonstrates that preterm birth remains a major challenge in modern obstetrics in the U.S., requiring further investigation to determine management options that may optimize obstetrical care and minimize unindicated preterm births,” Dr. Eran Bornstein, vice chair of OB-GYN at Northwell Lenox Hill Hospital in New York, told Healthline.

“Efforts to screen and identify patients at risk for spontaneous preterm birth and interventions that may reduce this risk are important.”

The report also calls for increased attention to pregnant people at risk for or living with certain chronic conditions to monitor their health and improve their prenatal care.

The CDC report does not cover reasons or indications for preterm deliveries, so the causes of the increase remain unclear and can only be speculated for now.

Bornstein cited several reasons for the increase in both spontaneous and iatrogenic [planned] preterm birth, including:

  • pregnancy at an older age
  • late or no prenatal care
  • obesity
  • hypertension
  • other medical comorbidities

“The report indicated that the largest change was for births at 37 weeks (an increase of 42%), which may reflect appropriate current practice to deliver women with certain high risk conditions at 37 weeks to decrease potential maternal or fetal complications,” Bornstein explained.

In some cases, iatrogenic preterm births, which are scheduled before 37 weeks for medical reasons due to maternal or fetal conditions, as well as pregnancy complications, may be necessary to protect the birthing person and the baby, Bornstein added.

In addition, many people delay childbearing until later in life due to many factors, which vary based on individual circumstances.

The medical term for people over 35 who become pregnant is “advanced maternal age,” said Dr. Kecia Gaither, MPH, double board certified in OB-GYN and maternal-fetal medicine and director of Perinatal Services/Maternal Fetal Medicine at NYC Health + Hospitals/Lincoln in the Bronx.

“With increased age comes an increased risk of attendant co-morbidities such as chronic hypertension, diabetes, and obesity,” Gaither told Healthline.

“These co-morbidities, particularly hypertension, can increase the risk of preterm deliveries. Preeclampsia’s incidence is increased with advancing age — the treatment of preeclampsia is delivery — and thus iatrogenic preterm deliveries often occur.”

Pregnancy at an advanced maternal age is increasingly common and associated with multiple risks.

Bornstein noted that people of advanced maternal age, particularly individuals over 40, have a higher risk of obstetrical complications such as:

“They are also more likely to have underlying medical complications (hypertension, diabetes, and more) at the time of conception compared to younger patients requiring optimization of these conditions and higher risk during the pregnancy,” Bornstein said.

According to medical experts, abortion bans could worsen preterm birth rates, particularly in southern and western states.

“Mothers with extremely high-risk conditions [who] conceive unintentionally and may have otherwise chosen to abort, [may] require early delivery due to their health issue. Women with [an] undesired pregnancy may be less motivated or have less access to quality prenatal care,” Bornstein added.

“In specific cases of multifetal gestations (especially triplets or more), fetal reduction is an important intervention to reduce preterm birth rates and optimize the outcome. This would not be legal to perform under an abortion ban,” he noted.

The report also highlights racial disparities between Black people and their white and Hispanic counterparts.

Past research has noted these disparities could be the result of “weathering” (premature aging caused by to the stress of racism).

“Racial disparities are another mediator increasing the risk of preterm labor,” Gaither said.

“Racism induces stress. Stress induces the constant production of the stress hormone cortisol, [which] impacts immune competence, blood pressure regulation, uterine contractility, and hemostatic ability. The constancy of stress does induce “weathering” in non-white women’s life experiences, impacting their overall health,” Gaither added.

Another factor that may be playing a role is epigenetics. External environmental factors may affect health.

“What is being seen among nonwhite women and their perinatal outcomes is reflective on what they experience due to racism’s impact on a daily basis,” Gaither explained.

“Add to that dynamic racial bias in the medical arena where nonwhite women aren’t being heard, discounted — it’s no surprise that disease pathology is noted exponentially among this particular demographic of women,” she noted.

Racism and racial disparities are a public health threat with transgenerational effects — not just for pregnant people, but to their offspring as well, Gaither said.

Preterm labor and preterm delivery may affect newborn health outcomes, leading to dysfunction in areas including:

  • ocular
  • pulmonary
  • hematologic
  • central nervous system
  • gastrointestinal health

Premature birth rates have increased in the U.S. over the last decade, but the reasons are unclear.

There are potentially many different factors driving the increase, including exposure to “everywhere chemicals,” pregnancy at a later age, obesity, and lack of quality prenatal care.

Abortion bans, racial disparities, and racism may also contribute to rising preterm birth rates.

If you’re pregnant or wish to become pregnant and live with a chronic health condition, talk with your doctor or OB-GYN to ensure you get the prenatal care you need.