The number of American babies who died before their first birthdays rose last year, significantly increasing the nation’s infant mortality rate for the first time in two decades, according to provisional figures released Wednesday by the National Center for Health Statistics.

Infant and maternal mortality, inextricably linked, are widely considered to be markers of a society’s overall health, and America’s rates are higher than those in other industrialized countries.

The increase in infant mortality comes after a century of public health improvements, in which rates consistently and gradually declined almost every year with few exceptions, said Danielle M. Ely, a health statistician with the NCHS and the report’s lead author.

The report did not delve into the cause of the increase, but most of the babies born in 2022 were conceived in 2021, when maternal deaths rose 40% because of the pandemic and many pregnant women were taken ill.

“Seeing an increase that hits the statistical significance mark indicates that this was a bigger jump than we’ve had in the last 20 years, and that is something we need to keep an eye on to see if it’s just a one-year anomaly or the start of increasing rates,” Ely said.

Some 20,538 infants died in 2022, representing a 3% increase over the 19,928 babies who died in 2021. The infant mortality rate — defined as the number of babies who die before they are 1 year old for every 1,000 live births — also increased by a statistically significant 3% last year, to 5.6 infant deaths per 1,000 live births, up from 5.44 deaths per 1,000 live births in 2021, according to the new report.

Black infants have the highest mortality rate in the United States, rising slightly last year to 10.86 deaths per 1,000 live births, from 10.55 deaths per 1,000 live births in 2021, an increase that was not statistically significant.

Among white infants, the figure rose to 4.52 deaths per 1,000 live births from 4.36 deaths per 1,000 live births in 2021. Among Native American and Alaska Native babies, the figure increased to 9.06 deaths per 1,000 live births from 7.46 deaths per 1,000 live births in 2021.

The two leading causes of infant deaths that were more prevalent last year were bacterial sepsis, caused by the body’s overwhelming reaction to an infection, and maternal health complications.