I know that 40 is just an idea in the mind—a finish line that isn’t one.

—Sheila Heti, from Motherhood: A Novel

Childbearing is a fraught topic at any point during a woman’s life, but rarely is it more so than during the run-up to the fifth decade, when conventional wisdom—if not science—suggests a golden door slamming shut. It’s an inflection point of which Sheila Heti’s forthcoming book, due out in May, is the latest, but certainly not the only, investigation: As her narrator grapples with her own ambivalence, so, too, does a generation that came of age with a sense that possibilities will always be infinite. Women who accept that they might not reproduce, or decide not to, wonder if they should feel differently; those who desire children and don’t yet have them sometimes slip into a panic, as if a single birthday might be the hinge on which a fulfilling life pivots. Being a pregnant 40-year-old, as the women depicted here are (or just were), might not be all that different than being pregnant at any other age, but it tends to elicit fascination, or relief, in one’s contemporaries; I know because I was recently one myself.

Is it really such a big deal, though? Popular culture serves up outliers, like Janet Jackson and now Illinois Senator Tammy Duckworth, who is pregnant with her second child at 49 (she had her first at 47) and recently revealed in an interview that her fertility doctor told her “50 is the new 40.” But popular culture is also responsible for the ticking-time-bomb neuroses of Bridget Jones and Charlotte York—the widespread perception, in the words of Naomi Watts’s childless 40-something in the Noah Baumbach comedy While We’re Young, that “after 35, it’s a shit show.”

The reality is that for a majority of women, it’s not. Many common impediments to fertility have nothing to do with a woman’s age; some, such as the widely reported decline in sperm counts, have nothing to do with a woman at all. In truth, the cliff isn’t usually 35, or even necessarily 40; it’s probably closer, on average, to 44 or so, though donor eggs can stretch those numbers further, and everyone is different.

In fact, the 40-to-44 and 45-to-49 age brackets are the ones in which U.S. birth rates—despite record lows overall—are rising fastest. This phenomenon is particularly easy to observe in cities like New York and Los Angeles, where career and coupling are competitive sports, and where my own obstetrician reassured me, during my first ultrasound last year at age 39, that more than half his patients were older than I was. “My college roommate is due one day before me; I’ve found quite a few other people my age are having kids within months of me,” says Amber Feld, a 40-year-old Los Angeles publicist expecting her first baby in April. “I was really surprised. I thought I might be the last, but I don’t think I will be even close to last.”

None of the women photographed for this portfolio planned specifically to have children at 40 or beyond; things just shook out that way. Their reasons for late childbearing—not that some explanation ought to be required—are as diverse as they are. Some needed time to find the right partner in the era of the left swipe; some paired off early and happily, then discovered fertility struggles that took years to resolve. Others remained of two minds about the prospect of parenting until the perceived last minute. Aya Kanai, a 40-year-old fashion director, conceived through IVF using eggs she froze at 36; her daughter was born days after this portrait was taken. “I had this funny moment,” she says, “where I was like, ‘Ugh, now I’m going to be one of those annoying moms.’ ”

That sentiment hints at perhaps the most common source of anxiety for women considering reproducing in the middle of rich adult lives: a perceived loss of identity—of unfettered sexuality, professional tenacity, free will. For motherhood, as Rachel Cusk astutely described in her scorched-earth maternity memoir, A Life’s Work, “divides women from themselves, so that a woman’s understanding of what it is to exist is profoundly changed. Another person has existed in her, and after their birth they live within the jurisdiction of her consciousness. When she is with them she is not herself; when she is without them she is not herself.”

It’s a transformation that one can only truly understand by inhabiting it, though the mechanics—4:00 a.m. cluster feeds, spit-up stains, the sudden allure of Dansko clogs—require little explanation. Would it be easier or more difficult to adjust to all this at 40—at which point one might be rather attached to one’s ability to fly to Corsica on a whim or microdose LSD or manage a team of subordinates—than it would be at, say, 30? That depends on whom you ask, or the moment at which you ask them.

At 40, raising a 4-month-old daughter with a fellow divorcé I met at 38, I sometimes feel I’m still figuring out who I am, but I knew, when I decided to let it happen, and perhaps this is why I let it happen, that I could no longer go on as I had been, ruminating, shopping, forever dabbling in side projects and social scenes, getting by on my baby face. A couple of old flames were shocked, shocked, by the news, as if I’d forfeited my status as a free spirit. But what could be more rock ’n’ roll than making a life? Besides, spending so little time thinking about myself or attending bad art openings isn’t an adjustment; it’s a monumental relief. Only when, after about six weeks, I began to consider what came before her and what would come next—and to understand that everything that isn’t her is wretched by comparison, and that I must engage with all of it anyway—has the enterprise of mothering seemed in any way problematic. Luckily, I can barely keep track of where my iPhone is these days. My baby hasn’t sparked an existential crisis; she is meditation itself.

That’s not to say that a woman must become a mother to become whole, or that a come-from-behind victory in the race against Mother Nature warrants special recognition. But regardless of one’s take on parenthood, when one reaches one’s 40s, or at least when I did, the internal narratives constructed around numerical age—the “shoulds”—start to give way to a vivid presence of mind, a relinquishing of a control that was never there in the first place. Sooner or later, kids or no kids, we will realize that we are no longer young, but that, in turn, may leave us more open to becoming something different. “I feel more prepared for them—in my career, but also in my emotional state,” says Khanh Cruz, a 44-year-old New Yorker and design director whose second child arrived on Valentine’s Day. “I don’t think that it could have happened sooner.”