Many women in the U.S. are waiting longer than ever to have their first child.
Fifteen years ago, the mean age of a woman when she first gave birth was 24.9 years old. In 2014, that age had risen to 26.3.
"It doesn't sound like a big change," says T.J. Mathews, a demographer at the National Center for Health Statistics and an author of the report published online Thursday. But, he says, the small shift underscores some important trends.
First, the researchers found that an increase happened across all states and across all racial and ethnic categories, to one degree or another. The average age increased half a year for moms of Cuban descent, for example, while for non-Hispanic black moms it increased by about two years.
Women of Asian and Pacific Islander descent continue to have the highest average age at first birth — close to 30 years old. Women who identify as American Indian/Alaska Native or Mexican have the lowest average ages at first birth, at 23 and 24.
The main force pulling the average age to the older end of the spectrum is a decrease in the number of teen moms, the researchers say. Over the past 15 years, the proportion of first-time mothers younger than 20 years old dropped from 23 percent to 13 percent.
Bill Albert with the National Campaign to Prevent Teen and Unplanned Pregnancy calls the drop "one of the nation's great unheralded success stories of the past two decades." Overall, he says the teen pregnancy rate has halved since its peak in 1990, declining in all 50 states and among all racial and ethnic groups.
Why? The short answer, he tells Shots, is "less sex and more contraception," possibly due to a combination of factors including government investment in sex ed programs, a bump in the number of teens using long-acting forms of birth control, and even MTV shows like 16 & Pregnant and Teen Mom, which have demonstrated their potential to scare the bejesus out of young, would-be parents.
The teen birth rate is not declining because of an uptick in teen abortions. That rate has also decreased since the 1990s.
This shift in age among first-time mothers impacts public health, says Dr. Priya Rajan, a specialist in maternal-fetal medicine at Northwestern University. She says teen moms are at higher risk of serious medical complications like anemia and hypertension, and are more likely to give birth prematurely and to have small babies.
On the other hand, first-time moms who are over 35 also have a higher-than-average risk of pregnancy complications, and their numbers are growing in the U.S. Since 2000, the proportion of first-time births to women older than 30 and 35 each increased by a few percentage points. These older mothers contributed to the rise in the average age of first-time moms, the researchers say, but the decline in births to teen moms was more influential.
Rajan says it's "an overall great thing" that improvements in contraception and in reproductive technology have offered women more flexibility in when to have kids.
But, she adds, women should be aware that as they approach 40 they're more likely to face risks during pregnancy. "Sometimes there is a belief that there's no limit to when people can bear children," she says.
In the last 45 years, the mean age of first-time moms has gone up by five years — from 21.4 years old to 26.3. If teen pregnancies continue to decline, Mathews says, and there's no slowdown in first births to older moms, the trend will likely continue to climb.
" 'How much? Where? Among whom?' Those questions remain unanswered," says Mathews.
The U.S. is far from the top when it comes to pushing the age-at-first-birth limit. In some countries, the mean age of mothers when they start having kids is over 30.