Photo: Shutterstock/Joanna Rothkopf

We already know that the so-called “motherhood penalty” plays a key role in the persisting gender wage gap. Now, a new unpublished study suggests an age-related catch: When women in opposite-sex marriages have their first baby before the age of 25 or after the age of 35, they eventually catch up with their husband’s pay. But if they have a first baby between those ages, their pay never catches up. It’s what the New York Times has now dubbed “The 10-Year Baby Window.”

Of course, “The 10-Year Baby Window” happens to represent “the years when most women have children,” as the Times puts it. Perfect.

The findings come from an unpublished working paper by the Census Bureau. In it, researchers analyzed earnings records for opposite-sex married couples who had their first baby between 1978 and 2011; they found that the pay gap between spouses doubled a year after the baby was born. Overall, women earned $12,600 less than men pre-baby and $25,100 less post-baby. “After the child’s first year of life the gap continues to grow for the next five years, but at a much slower rate, then tapers off and even begins to fall once the child reaches school-age,” the study reports.

But when researchers looked at the age of mothers when they had their first child, “The 10-Year Baby Window” emerged, where the pay gap doesn’t close. The proposed explanations for this vital time period are about what you would expect: Parenthood—well, actually, specifically motherhood—often overlaps with these crucial career-building years. As the Times reports:

The issue, in general, comes down to time. Children require a lot of it, especially in the years before they start school, and mothers spend disproportionately more time than fathers on child care and related responsibilities. This seems to be particularly problematic for women building their careers, when they might have to work hardest and prove themselves most, and less so for women who have already established some seniority or who have not yet started careers.

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In other words, the thinking goes, it’s less detrimental for a woman to introduce a time-sucking baby into the equation if she’s at the very start of a career or has already weathered the “prove yourself” years. (Note that there is no similarly career damaging “10-Year Baby Window” for dudes. In fact, men reportedly experience a “fatherhood bonus.”)

But escaping that age-related penalty is easier said than done: When women wait to have babies well into their 20s, it’s often for exceedingly good relational, emotional, and financial reasons. On the other hand, waiting until your late 30s means contending with seemingly constant messaging about aging ovaries and egg-freezing and, oh dear god, the dreadful “geriatric pregnancy” label.

I just recently had a baby at the age of 33—after roughly a decade spent worrying about distressing, contradictory, and poorly-sourced fertility data, and two short years before I would have been officially deemed by doctors to be a “geriatric” or of “advanced maternal age.” I survived the culturally policed age-related fertility gauntlet, only to learn today that my reward might very well be to never make as much as my husband. I love a happy ending.