The US birth rate hit another record low in 2019. Experts fear we're facing a 'demographic time bomb' that could be fast-tracked by the pandemic.

• The US fertility rate declined 1% between 2018 and 2019, hitting a 35-year-low, according to a report out Friday from the CDC.
• The report also found that the percentage of mothers beginning prenatal care in the first trimester increased among white and Black women, but the preterm birth rate among all groups rose 2%.
• Experts say the ongoing baby bust is mostly due to couples delaying childbirth, and having fewer children if they do so at all.
• The dip is part of a global phenomenon, leading some experts to fear a "demographic time bomb," or when there aren't enough young people to support an aging population and the economy.

Fewer babies were born in the US in 2019 than in any of the 35 years before, continuing a trend some experts have warned could lead to a "demographic time bomb," or when fertility rates decrease as longevity increases.

The report out of the Centers for Disease Control and Prevention Friday found the US fertility rate declined 1% between 2018 and 2019, including among non-Hispanic white, non-Hispanic Black, and Hispanic populations.

It also found that the percentage of mothers beginning prenatal care in the first trimester increased among white and Black women, but decreased among Hispanic women. The preterm birth rate rose 2% from 2018 to 2019 among all groups, for the fifth year in a row, to more than 10%, the report found.

Experts say the ongoing "baby bust" seems to be mostly attributable to changing attitudes toward parenthood that are leading more people delay childbearing and have fewer children once they start, if they have children at all.

The trend is a part of a larger global phenomenon that the coronavirus pandemic is likely to exacerbate.

Preliminary data showed birth rates were down among younger age groups and up among women over 40

A preliminary report released in May that used a slightly less complete version of the same data broke down the birth rate decline by age groups.

It found births among teenage moms were markedly down once again. Between 2017 and 2018, for example, the birth rate among 15- to 19-year-old decreased 7%, and between 2018 and 2019, it decreased another 5%.

Women in their 20s were also less likely to give birth in 2019, and rates among 35- to 39-year-old women remained steady.

For women over 40, though, birth rates were up about 2%, maintaining a theme also seen since 1935.

"More couples are delaying starting their families due to career and other personal reasons," Dr. Eric Forman, medical and lab director at Columbia University Fertility Center, told Insider, adding that the good news is that options to have children later in life "are better than ever."

"There are excellent options to preserve fertility if the time is not right to have a child, for example, with egg freezing," he said.

But other experts worry some couples count on fertility treatments being more effective than they are. "While [assisted reproductive technology] is successful, it has limitations at older ages," Dr. Feinberg previously told Insider.

The declining birth rate is a global phenomenon that could lead to a demographic time bomb

The overall trend of decreasing birth rates has troubled some experts who say the United States could suffer a demographic time bomb in which there eventually aren't enough young people to support both the economy and older people who continue to live longer.

"From a societal perspective, there could be implications on the economy in the future if there is a declining population, as has been seen in some countries like Japan," Forman said.

At its most extreme, Insider previously reported, demographic time bombs could lead to the eventual extinction of a country's population.

The phenomenon isn't limited to the US. A Lancet study released in July predicted that nearly every country's population will shrink and some will halve by the end of the century because women are having fewer children.

In 1950, the average number of kids a woman had was 4.7. By 2017, it was 2.4. By 2100, the study authors predicted, it will fall below 1.7.

And once women have fewer than 2.1 babies each, the population on the whole declines. In fact, the researchers at the University of Washington's Institute for Health Metrics and Evaluation predicted the world's population will max out in in 2064 at 9.7 billion and tumble to 8.8 billion before the century's end.

"This study provides governments of all countries an opportunity to start rethinking their policies on migration, work forces, and economic development to address the challenges presented by demographic change," IHME Director Dr. Christopher Murray, who led the research, said in a press release.

It's unclear how the coronavirus pandemic will affect 2020 birth rates

While celebrities appear to be enjoying a baby boom, the coronavirus pandemic could have the opposite effect on the population at large. "Reviews of prior pandemics and major natural disasters with high mortality rates show that fertility rates decline in the aftermath," Forman told Insider.

Plus, many people who need medical help to get pregnant have needed to delay their fertility treatments. Some may not resume their care or may find it's too late once they're ready or able.

Other couples are holding off on conceiving naturally because so much remains unknown about how the virus affects pregnant women and their future children.

But the coronavirus's effect on birth control and abortion access could outweigh these changes. Only time will tell.

• Read more:
• Couples are being told to delay fertility treatments during the coronavirus pandemic. Some worry they'll miss the chance to have kids.
• The sharp decline in global fertility rates may lead to a demographic time bomb, with some populations expected to halve by 2100
• There are benefits to holding off on pregnancy during the coronavirus pandemic. It's still up to you, experts say
• The coronavirus 'baby boom' is only for the rich and famous. Most people are too terrified to think about having kids right now.