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NEW YORK (AP) — For the first time, women in their early 30s are having more babies than younger moms in the United States.

Health experts say the shift is due to more women waiting longer to have children and the ongoing drop in the teen birth rate.

For more than three decades, women in their late 20s had the highest birth rates, but that changed last year, according to preliminary data released Wednesday by the Centers for Disease Control and Prevention.

The birth rate for women ages 30 to 34 was about 103 per 100,000; the rate for women ages 25 to 29 was 102 per 100,000. The CDC did not release the actual numbers of deliveries for each age group.

It's becoming more common to see older parents with kids in elementary or high school, said Bill Albert of the National Campaign to Prevent Teen and Unplanned Pregnancy.

Meanwhile, more teens are growing up with fewer of their peers getting pregnant, he said.

"We always talk about peer pressure as a negative, but it can be a force for good," Albert said.

A separate CDC report focusing on deaths found the nation's overall death rate fell last year after an unusual and worrisome increase in 2015.

The reports are based on a first look at birth and death certificates filed across the country last year.

Among the findings:

— The overall birth rate was down slightly in 2016, to 62 births per 100,000 women ages 15 to 44.

— The average age when women have their first child is about 28.

— The teen birth rate continued to drop last year.

—The infant mortality rate stayed about the same.

—The overall death rate fell to about 724 per 100,000 people in 2016, down from 733 the year before.

Experts said the 2015 increase was tied to an unexpected leveling off in the death rate from the nation's leading killer, heart disease.

Heart disease and stroke deaths were falling steadily until 2011, but then the annual decreases shrank. In 2015, the heart disease death rate increased nearly 1 percent, and started to go down again in 2016.

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Now it seems like 2015 may have been blip, "but we can't tell right now what will happen next year or in the next couple of years," said Dr. Stephen Sidney, a researcher at Kaiser Permanente Northern California who has written on heart disease death trends.

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