Declining birth rate in US

NPR is reporting that, for the second year in a row, the birth rate in the US declined sharply.  2017 witnessed the fewest number of live births in the US since 1978.  That year, the total US population was about 225 million, a hundred million fewer than today.

The NPR report notes that women of different child-bearing age groups contributed to the decline:

Broken out by age, the 2017 birthrate fell for teenagers by 7 percent, to 18.8 births per 1,000, a record low. That figure is for women from 15 to 19 years old. For that same group, the birthrate has fallen by 55 percent since 2007 and by 70 percent since the most recent peak in 1991, the CDC said.

Women in their 40s were the only group to see a higher birthrate last year. Between the ages of 40 and 44, there were 11.6 births per 1,000 women, up 2 percent from 2016, according to the CDC's provisional data. 

Birthrates fell by 4 percent both for women from 20 to 24 years old and for women of ages 25 to 29. 

For women in their 30s — a group that had recently seen years of rising birthrates — the rate fell slightly in 2017. The drop included a 2 percent fall among women in their early 30s, a group that still maintained the highest birthrate of any age group, at 100.3 births per 1,000 women.

In terms of the impact on the country, the article notes:

The results put the U.S. further away from a viable replacement rate – the standard for a generation being able to replicate its numbers. 

"The rate has generally been below replacement since 1971," according to the report from CDC's National Center for Health Statistics. 

The CDC calculates a "total fertility rate" by estimating how many babies a hypothetical group of 1,000 women would likely have over their lifetime. That measure now stands at 1,764.5 births per 1,000 women — a 3 percent drop from 2016. The replacement rate is 2,100 births per 1,000 women.

David Meyer of Fortune magazine calls out the importance of the replacement rate:

The obvious problem stemming from the overall decline is that America’s population is aging, which means more older people who may need a social safety net and fewer younger people to pay into the systems that provide it.

It's commonly thought that the birthrate is a reflection of people's confidence in the country and the times they live in: if they're optimistic, they have babies; if they're not optimistic, they defer having babies.  In a LiveScience article, Karen Benjamin Guzzo from Bowling Green's Center for Family and Demographic Research follows this line of thought:

"People feel just really uncertain about the future," Guzzo told Live Science. "And that generally does not bode well for having kids."

But that uncertainty is difficult to square with the economy.  According to AP medical writer Mike Stobbe:

baby booms often parallel economic booms, and last year was a period of low unemployment and a growing economy.

Stobbe suggests some other factors that may be at work in the decline:

One may be shifting attitudes about motherhood among millennials, who are in their prime child-bearing years right now. They may be more inclined to put off child-bearing or have fewer children, researchers said.

Another may be changes in the immigrant population, who generate nearly a quarter of the babies born in the U.S. each year. For example, Asians are making up a larger proportion of immigrants, and they have typically had fewer children than other immigrant groups. 

Also, use of IUDs and other long-acting forms of contraception has been increasing.

The LiveScience article also asks an interesting question about number of moms vs. number of kids:

Guzzo noted that the new report looked at overall births but didn't examine "birth order" — that is, whether the births were a woman's first, second or third child, and so on. So it's unclear from the current report whether women are having fewer kids overall (firstborns) or having smaller families; previous data suggested that the latter may be the case, Guzzo said. The CDC will examine birth-order data for 2017 in a follow-up report.  

What do you think it all means?