The fertility rate in the U.S. dropped by 4% last year compared to 2019, the lowest it's been in nearly 50 years, according to provisional data from the National Center for Health Statistics.

Why it matters: The data corroborates previous surveys that predicted a "COVID baby bust," with women reporting they were postponing pregnancy and having fewer children, as well surveys indicating less sexual activity overall.

By the numbers: There were 55.8 births per 1,000 women aged 15 to 44 last year. It is the sixth straight year the number of births in the U.S. have fallen, CDC data shows.

• There was an overall decline in all age groups between 15 to 44. Brady Hamilton, the lead author of the study, called those drops "unusual" and "extraordinary." Births had been rising for women in their 30s, he said.
• The preterm birth rate declined for the first time since 2014 to about 10% in 2020.

The big picture: Fertility rates in the U.S. and around the world have been falling for years as women in developed countries have gained more freedoms, received more education, and in some cases, gotten increased access to birth control.

Yes, but: Though significant, the decrease of 142,000 births last year is about half of what experts predicted. Researchers saw closed child centers and schools as key reasons for slowed births.

In a separate study published Wednesday, the NCHS found that more women in New York City, once the epicenter of the pandemic in the U.S., left to give birth in 2020 than in 2019.

• Out-of-city births peaked in April and May with about 10% of women leaving the city compared to about 6% in 2019. This was especially true for white women, per the report.

Go deeper:The uncertain future of human reproduction