The study found that just shy of 230,000 girls age 15 to 19 gave birth in 2015, or 22 for every 1,000 teens, which was an 8% decrease from 2014. The birth rate in this age group has been falling sharply since 2007, and between 2013 and 2014, there was a record decrease
Even though the decrease in teen birth rate between 2014 and 2015 does not appear to be quite as large as between 2013 and 2014, it is "still quite impressive," said Brady E. Hamilton, a statistician and demographer at the National Center for Health Statistics who is lead author of the study.
Since 2007, the year-to-year decline in teen birth rates has been between 7% and 9%, which is "just astounding compared to change for any other age group," Hamilton said. The number of teens becoming moms has dropped by a total of 54% from 2007 to 2015.
The number of women giving birth in their 20s has also been declining, albeit more gradually, since 2007. The birth rate among women between 20 and 24 dropped 27% between 2007 and 2015; in the most recent years, the decrease was 2% from 2013 to 2014
(PDF) and 3% from 2014 to 2015. Among women 25 and 29, the birth rate has been waning by about 1% each year, with the exception of a small bump of 2% between 2013 and 2014.
In contrast, the birth rate among women in their 30s rose about 1% from 2014 to 2015, contributing to an ongoing trend. The number of women between 30 and 34 giving birth has increased 5% since 2011 to 101.4 births per 1,000 women in 2015; the number of moms 35 to 39 climbed 13% since 2010 to 51.7 births per 1,000 women in 2015.
There was a relatively big spike of 4% in the birth rate among women 40 to 44 from 2014 to 2015, although the number of births in this age group was still low, at 11 per 1,000 women.
The report adds to the evidence that the age of mothers is rising in the United States, Hamilton said. A report
by the CDC in January found that the average age when women had their first child increased from 24.9 in 2000 to 26.3 in 2014.
"There have been technological changes that make birth control easier and changes in women's economic standing ... which would be consistent with the notion that women want to delay and have better methods of delay," said Phillip Levine, professor of economics at Wellesley College. Women are getting more education and contributing to the household income, and "to take advantage of that, it makes sense to delay childbearing," he said.
The big improvements in birth control technology are the emergency contraception pill
and long-acting reversible contraceptives
, known as LARCs, which include intrauterine devices and contraceptive implants. LARCs have failure rates
(PDF) of less than 1%, whereas condoms and birth control pills result in pregnancy in 18% and 9%, respectively, of cases.
The number of women ages 15 to 44 using LARCs has been steadily increasing from 2.4% in 2002 to 8.5% in 2009 to almost 11.6% in 2012, according to a report
by the Guttmacher Institute.
The main factor that probably jump-started the sharp decline in birth rates among teens in 2007 was the Great Recession, Levine said. "I think teens are capable of responding to environmental conditions in similar ways to adults, and if it is not a good time for adults to have a baby, it is not a good time for a teen to have a baby," Levine said.
The teen birth rate has continued to drop even now that the recession has ended and the economy is recovering, probably because more teens started using LARCs. "But its uptake is not huge, and there is certainly room for improvement," Levine said.
According to the Guttmacher report, less than 6% of women age 15 to 19 were using a LARC in 2012.
The report also found that the number of babies born by cesarean is continuing to decline, from its peak of 32.9% in 2009 to 32% in 2015. Part of the decline could be because ob-gyns are less willing
to perform cesarean deliveries because of the growing understanding that it is riskier for the mother.
There was a slight increase in the rate of preterm births, from 9.57% in 2014 to 9.62% in 2015, the first increase since 2007. The number of babies with low birth weight also inched up from 8% in 2014 to 8.07% in 2015 for the first time since 2007.
The findings are considered preliminary until all the birth records in the United States in 2015 have been processed, Hamilton said. The final report should be available in October. In previous years, the preliminary reports tended to agree with the final report, Hamilton said.