For the first time ever, more women are giving birth in early their 30s than in their late 20s, and it’s totally changing average birth rates nationwide.

Women ages 25 to 29 have had the highest rate of birth for over three decades, but the early-30s bracket recently took the top spot, according to preliminary 2016 research from the Center for Disease Control. According to their data, women aged 30-34 are giving birth at a rate of 103 births for every 100,000 people, compared to 102 births per 100,000 for the 25 to 29 bracket.

This change in birth numbers sets the average age for giving birth to 28, which is up from 26 just two years earlier.

This research comes as the number of women in the workforce reaches an all-time high, with more women in high-power positions than ever before in U.S. history. Despite this growing demographic, the U.S. remains the only developed nation without a paid maternity leave program.

As women grow in their careers, they do so knowing their position and income may not be protected if they have a baby.

“What you’re seeing is people who were not having children in their 20s are now having children in their 30s,” Elizabeth Gregory, author of "Ready: Why Women Are Embracing the New Later Motherhood" told ATTN:. “Women (are) investing their time first in education in order to get better jobs and then support their children because there is no infrastructure that supplies child care. If you’re looking to support [a child], a lot of people figure, ‘well, I need to get myself in a position where I’m going to be making a good wage.’”

Maternity leave is more likely to be accessible in higher ranking, higher paying positions, which may lead women to wait until later in their professional lives to have children. Research conducted by Pew in 2015 showed that 40 percent of the public believed women should wait until they are well established in their career to pursue motherhood, and one-fifth of the public believed that women shouldn’t have children at all if they hope to progress professionally.

People who weren't having children in their 20s, now having children in their 30s.

“You can take leave, but it isn’t paid,” Gregory said of many maternity leave policies in the United States. “So unless you’re in a position to cover that yourself there’s sort of a built-in push towards delay, just because there’s a lack of any other kind of benefits for parents.”

Beyond the workplace, a record low in teen births may have also contributed to the dip in the average birth giving age. In 2016 there were less than 25 births for every 100,000 teenage females in the United States. That's a serious drop from the late 1990s, when there were 93 pregnancies for every 100,000 teen girls.

The shift in birthing age comes as birthrates hit the lowest recorded point in U.S. history. In the first three quarters of 2016, there were less than 60 births for every 100,000 women between the ages of 15 and 44 in the U.S., according to the National Center for Health Statistics. That’s less than half of the average birth rate recorded during the peak of the Baby Boomer era, and it’s even down half a percent from the previous year.