The birthrate in the United States increased slightly last year, ending what had been a consistent decline since 2014, the federal government reported on Tuesday.

There were 3,659,289 births in 2021, an increase of about 46,000, or 1 percent, from 2020, when there was a sharp drop, according to provisional data released by the National Vital Statistics System, part of the Centers for Disease Control and Prevention.

The increase can likely be attributed to parents making peace with the conditions of life during a pandemic, according to Phillip Levine, an economist at Wellesley College who has studied recent fertility trends.

During the initial Covid-19 lockdowns in the spring of 2020, there was a sharp decline in conceptions that led to births, according to his analysis. (Despite frequent speculation, there typically aren’t baby booms nine months after blizzards, blackouts and other one-off events that leave couples home alone and bored.)

But by the summer of 2020, conceptions were on the rise, as the unemployment rate dropped and government benefits reached families. And as the pandemic wore on, local infection rates did not seem to factor much into people’s decisions about childbearing.

“Our acceptance of the Covid environment grew,” Professor Levine said.

Still, not all women were equally confident in having a baby during the pandemic. While the birthrate rose 2 percent for white and Hispanic women, it declined by 2 percent to 3 percent for Black, Asian and Native American women.

The birthrate dropped to record lows for teenagers and declined 2 percent for women 20 to 24. Women in their 30s, who are more likely than younger women to be married and financially stable, experienced the greatest uptick in fertility.

One of them is Michaela Howard, 35, of Richmond, Va. She and her husband, both professionals in the nonprofit sector, welcomed their first child, Henry, in November 2021, after seven years of marriage and some debate about whether parenthood was something they desired.

“One of the biggest hesitations for me and my husband has always been climate change and what kind of world we’re bringing a child into,” Ms. Howard said. Then the pandemic hit. For months, the couple felt as if life were “on hold.”

But in early 2021, with Covid-19 vaccinations on the horizon, they chose to embrace optimism and conceive. “I felt like it would be something that would bring me joy in my life, and to put it off would be denying myself that opportunity,” she said.

The C.D.C. data shows that 10 percent of babies were born preterm in 2021, the highest rate since 2007. For the second year in a row, the cesarean delivery rate rose slightly, to 32 percent.

The uptick in fertility does not change the country’s overall demographic picture. Since 2007, fertility has generally been in a free fall. And while the birthrate went up in 2021, it is still lower than in 2019. More parents are choosing to have only one child.

“I’m not going to get too excited about this,” said Kenneth Johnson, a demographer at the University of New Hampshire. “It’s really a very modest increase.”

Experts debate why American women have had so few babies over the past 15 years. The millennial generation has lived its young adulthood amid two crises that could have affected their desire or ability to raise children: the pandemic and the Great Recession, which began in 2007, around the time the birthrate began to drop. Many millennials are burdened with student loans and high costs for housing and child care.

Professor Johnson likened the experience to living through the Great Depression, which caused a stark decline in births.

But social scientists say they are increasingly looking at another explanation for low fertility — a broad, international shift in young women’s attitudes and goals. More women are choosing to prioritize education and work, marrying later and having fewer or no children.

A recent paper by Professor Levine and colleagues did not find evidence to link state birthrates to child care costs, student debt or rental housing costs. The paper also demonstrated that across high-income countries with social safety nets far more generous than in the United States, fertility has long been well below the replacement level of 2.1 children per woman. Policies intended to encourage fertility have had only a modest, short-term effect.

The decline in American fertility appears to be following the path already tread by countries like Japan, Britain and Sweden.

A lower birthrate raises questions about long-term national economic growth. There will be fewer working adults to finance programs like Social Security and Medicare.

“The simplest solution to the problem is increased immigration,” Professor Levine said.

“That is politically tenuous,” he said. “In a world in which you have to live with a lower fertility rate,” he added, “you have to think about being more efficient in investments in the educational system and in infrastructure — things that will advance us as a society that don’t come from just more people.”