If you’re a mother, did you have your kids when you were young? Or did you get them in (or out, actually) just before the curtain of menopause dropped? It makes a difference, it turns out, in female life expectancy–how long you can expect to live.

Scientists have figured out a key indicator of longevity: leukocyte telomere length. That may sound like something to do with what a palm reader sees in your lifeline, but it’s actually scientific. The longer the telomeres are, the more birthdays you can expect to celebrate, and the older you were at the birth of your last child the longer the telomeres tend to be, according to a recent study published in Menopause, the journal of The North American Menopause Society.

So what the hell are telomeres? They are the protective caps on the ends of the strands of DNA called chromosomes, which house our genomes. Their job is to stop the ends of chromosomes from fraying or sticking to each other, much like the plastic tips on the ends of shoelaces. They shorten with each cell division, however, and when they reach a critical length the cell stops dividing or dies.

Read More: Why Some Women Breeze Through Menopause. And Others Don’t

Female Life Expectancy Factors

This is not the first time that the length of a woman’s leukocyte telomeres has been linked with health and female life expectancy. Previous studies have suggested a link between telomere length and various chronic conditions such as cardiovascular disease, type 2 diabetes, some neurologic conditions, and various cancers.

A smaller study previously suggested that maternal age at the birth of a woman’s last child affected telomere length. This new, larger-scale study included more than 1,200 perimenopausal and postmenopausal women of various ethnicities and backgrounds from the National Health and Nutrition Examination Survey.

This finding was restricted to women with one or two live births or who had used oral contraceptives. In addition, unlike previous studies, this study took into consideration sociodemographic factors related to childbearing patterns and health decisions.

“More research is needed to determine whether older maternal age at last birth causes telomeres to lengthen,” says Dr. Stephanie Faubion, NAMS medical director. “Or whether telomere length serves as a proxy for general health and corresponds with a woman’s ability to have a child at a later age.”

So maybe those babies who came when their moms thought it was too late to conceive are miracles in more ways than one.

Read More: How Old Do You Feel? Why That’s Such An Important Question as We Age