By Nancy Lapid

(Reuters) -Stillbirths in the U.S. are more common than previously reported, affecting roughly 1 in 150 pregnancies, and rates are even higher in lower-income areas, according to results from a large study published on Monday.

The national average reported by the U.S. Centers for Disease Control and Prevention is 1 in 175 pregnancies.

The CDC's main source of data - fetal death certificates collected by individual states – is less reliable than the commercial insurance claims data used in the new study, researchers said.

“Both of these data sources - the data in our study and the CDC data - have potential flaws, but the main issue is that, regardless of data source, the rate of stillbirths is too high,” said study co-leader Jessica Cohen of the Harvard T.H. Chan School of Public Health.

“The U.S. has among the highest rates of stillbirth among all high-income countries and there has been barely any improvement in stillbirth rates in recent years,” Cohen said.

The new study, reported in JAMA, does not include deliveries covered by the government Medicaid program for low-income Americans. But pregnancy outcomes “are, if anything, worse, in Medicaid-covered pregnancies so we may expect that the stillbirth rate is even higher in the Medicaid population than what we find here,” Cohen said.

DATA DETAILS AND RISK FACTORS

Analyzing more than 2.7 million pregnancies across the U.S. between 2016 and 2022, the researchers identified 18,893 stillbirths, defined as the death of a fetus at 20 weeks gestation or greater.

More than 70% were in pregnancies with at least one maternal risk factor, suggesting they might have been preventable.

Stillbirth rates were highest among pregnancies with low amniotic fluid levels, fetal anomalies, and chronic hypertension. Other risk factors included maternal diabetes, obesity, and substance use.

Medical guidelines call for close monitoring of pregnancies in the presence of these risk factors, such as with increased ultrasound exams or fetal heart rate testing, said study co-leader Dr. Mark Clapp of Massachusetts General Hospital in Boston.

Rural versus urban residence and access to obstetric care were not linked with stillbirth risk.

But the stillbirth rate rose to 1 in every 112 births in low-income areas, and it was 1 in every 95 births in areas with higher proportions of Black families compared to white families, the study found.

The sociodemographic characteristics of the area where individuals live are not included in clinical guidelines for intensified monitoring of pregnancies, Clapp noted.

The drivers of this socioeconomic variation in stillbirth rates, whether social factors, health systems factors, or clinical risk factors, need to be investigated, he said.

A substantial share of stillbirths occurred in the absence of any known clinical risk factors, the researchers also found. This was particularly true for later-term stillbirths.

“Many stillbirths are potentially preventable, and we can lower the stillbirth rate in the U.S., but not without attention, research, and resources,” Cohen said.

(Reporting by Nancy Lapid; Editing by Bill Berkrot)