The increases were particularly stark among babies born to Native American, Alaska Native and white mothers in 2022. Rates among Black infants remained highest of all.

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.

The spike is a somber manifestation of the state of maternal and child health in the United States. 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 rates are particularly poor among Black and Native American mothers, who are roughly three times as likely to die during and after pregnancy, compared with white and Hispanic mothers. Their infants face up to double the risk of dying, compared with white and Hispanic babies.

Overall life expectancy has declined in the United States in recent years, too, affecting white Americans as well as people of color. The declines were driven in part by the Covid-19 pandemic.

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 N.C.H.S. 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 by 40 percent 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,” Dr. Ely said.

One of the more disturbing findings was an increase in infant mortality among babies born to women ages 25 to 29. The rate increased to 5.37 per 1,000 live births last year, up from 5.15 deaths per 1,000 live births in 2021.

Rates did not change for women in other age groups, even those who generally experience higher infant mortality rates, such as women younger than 20, those 20 to 24 and women 40 and older.

Some 20,538 infants died in 2022, representing a 3 percent 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 a year old for every 1,000 live births — also increased by a statistically significant 3 percent 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.

The mortality rate of babies who were between 4 weeks and a year old increased by 4 percent, while neonatal mortality rates — that of babies less than a month old — increased by 3 percent.

Rates increased significantly among both premature babies born before 37 weeks of gestation and those born extremely early, at less than 34 weeks of gestation.

Overall, the statistically significant increases in mortality rates were seen only among male infants, whose survival rates have always been slightly lower than those among females.

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.

By contrast, the infant mortality rates of both white and Native American and Alaska Native babies increased by statistically significant amounts last year.

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.

Since infant deaths are relatively rare events involving small numbers of babies, statistically significant changes cannot easily be seen from year to year at the state level. Nevada was the only state that had a statistically significant decline in infant mortality, while four states — Georgia, Iowa, Missouri and Texas — experienced statistically significant increases in infant mortality last year.

Texas banned abortions after six weeks of pregnancy in 2021, which may have played a role in the larger number of infant deaths the following year by preventing terminations of acutely ill fetuses.