The United States has just set a new record for twin births, reaching 33.9 out of every 1,000 births, an increase from the 2013 rate of 33.7.

It’s not a statistically significant increase, but it does technically qualify as a new high, based on statistics from the National Center for Health Statistics, according to a Los Angeles Times report.

The racial breakdown is 7,788 born to white women, 23,546 born to black women, and 22,051 born to Latina women.

The record for twins rate was actually set last year, but the total number of twin births was actually down to just the 5th highest of all time after 135,336 were born last year in the United States. The all time high was 138,961 in 2007.

So what is driving this increase? Apparently women tend to wait longer these days before having children, with the average age of first-time moms increasing to a new U.S. record of 26.4 years in 2014, while the birth rate for women in their teens and early 20s fell.

Fertility tends to decrease when women get older, but it also tends to increase the likelihood of twins. Why? Scientists think because the ovaries are low on eggs resulting in more hormones that causes the release of multiple eggs more often. This can result in a higher rate of twins, potentially.

This only applies to fraternal twins, not identical twins, however. Scientists haven’t found any link between the age of a mother and the odds of identical twins.

Overall, the birth rate of twins is up 79 percent since 1980.

A total of 4,256 babies were born as triplets or higher multiples, the lowest since 1993.

The statistics are based on 3,988,076 babies born in the United States in 2014, a 1 percent increase from 2013. It includes all 50 states as well as the District of Columbia and U.S. territories.