The following is adapted from Dunn’s How Not to Hate Your Husband After Kids, published by Little, Brown.

Two months into our daughter’s existence, my husband, Tom, and I nearly came to blows over whose turn it was to empty the Diaper Genie, whose plastic entrails had become bloated and coiled like a postprandial Burmese python. Normally we’re peaceable types, so the volcanic ferocity of our anger surprised us both. I remember glancing down at my hands, clutching the Genie sack, and envisioning them around Tom’s neck. When he yelled that he did it “last time,” I hollered back that I had carried and delivered the baby “the last time.” This was a tired, if effective, retort.

On this upcoming day of celebrating mothers, here’s a cautionary note, something many mothers-to-be don’t expect when they’re expecting: If you have a husband, you will hate him when your kid is born. Don’t let anyone tell you otherwise. Don’t be fooled by the pictures on your social media feed of your friends serenely beaming with their infants. When they’re not letting you know they’re #SoBlessed, they’re probably fighting.

Perhaps the single most widely cited piece of research on marriage and children comes from couples’ therapists John and Julie Gottman, who found that 67 percent of couples are less satisfied with their marriages after having a baby. A 2009 study of first-time parents in the Journal of Personality and Social Psychology found that a scant 7 percent of mothers reported feeling more satisfied with their marriage, compared with 15 percent of fathers. (As of now, the available research is much more robust for heterosexual couples.) Many factors conspire to shorten a new parent’s fuse: hallucinatory fatigue, zigzagging hormones, a fraught learning curve, and, as one paper I read noted succinctly, “increased interactions with medical professionals.”

All the advice for new parents about sleep schedules and burping techniques would be much more helpful if the belligerence of the early days of parenthood was more openly addressed—as well as how gendered that unhappiness often is. Take the contested terrain of sleep deprivation. Researchers from the U.K.’s Mindlab International found that while a baby’s cry was the No. 1 sound most likely to wake a woman, it didn’t even figure into the male top ten, lagging behind car alarms and strong wind. They theorized that these differing sensitivities may have an evolutionary basis: Women are more attuned to threats to their offspring while men are more responsive to threats to the clan (e.g., the Toyota being jacked in the night).

If women are breastfeeding, they typically wake two to three times a night to nurse, which wreaks havoc with their REM sleep cycle. When children move past babyhood, working moms are still 2½ times as likely as working fathers to interrupt their sleep to take care of others. This is not the case with fathers: Earlier this year, researchers from Georgia Southern University found that while women with children were getting insufficient sleep, the presence of children had no effect whatsoever on men’s sleeping patterns.

So the odds are high that you will fight over who gets up with your offspring at night. If I heard the slightest whimper from our daughter, I would rocket out of bed like a Delta Force commando given the go signal for a nighttime raid. In the meantime, he snored peacefully. Perhaps it’s not surprising that in the U.S. government’s American Time Use Survey, women reported feeling significantly more fatigued than fathers in all four major life categories: work, housework, leisure, and child care.

There will also be fights about chores and child care. While the lives of women, who now make up almost half of the U.S. labor force, have changed radically in the past few decades, the behavior of their mates has not changed quite as much. A few depressing lines from a 2012 study of first-time parents neatly summed up the colossal asymmetry I experienced with my husband: “As found in prior research, mothers experienced unmet expectations with fathers doing less than mothers expected. Fathers, on the other hand, experienced overmet expectations with mothers doing more than fathers expected.”

I thought I had married an evolved guy—one who assured me, when I was pregnant, that we would divide up the work equally. Yet right after our baby was born, we backslid into hidebound midcentury gender roles as I energetically overmet my expectations. I was feeding the baby, so I started cooking for the whole family (pre-baby, Tom and I had alternated). I was laundering our daughter’s absurdly large mountain of soiled onesies, so I took over laundry duty. Soon I was the “expert” in changing a diaper.

We’re not alone: A 2015 Ohio State study of ​working couples found that men did a fairly equal share of housework—until, that is, they became dads. By the time their baby had reached nine months, the women had added more than two hours of daily work, the men a mere 40 minutes.

And Tom, while a kind, sensitive sort of person, rarely seemed to notice that I needed a hand, lounging on the couch and happily playing SocialChess on his phone while I simultaneously tended our child, emptied the dishwasher, and made dinner. Social psychologists say that men simply feel more entitled to take leisure time. Researchers for the UCLA Center on the Everyday Lives of Families found that a father in a room by himself was the “person-space configuration observed most frequently” in their close study of 32 families at home.

A UCLA study of married couples found that at the end of a workday, women’s stress levels went down if their husbands pitched in with more housework. No surprise there. The mind-boiling part is that men’s stress levels fell if they kicked back with any sort of leisure activity—but only if their wives kept busy doing household tasks at the same time. If they both did leisure activities, the men’s stress levels stayed put.

If I would ask Tom to do the dishes after I made dinner, he’d tell me he was going to “let them soak.” That phrase set me off like a Roman candle. Then I figured out why: because women tend to be the ones to do time-associated tasks all throughout the day that involve deadlines, like meals and school drop-offs, so they are programmed to jump immediately. Responses like “later” or “in a minute” treat a task like an option. They rankled me as much as Bartleby’s “I would prefer not to” exasperated his hapless boss.

If my husband and I had known that fighting was what we should have expected when we were expecting, maybe we would have been better prepared. Eventually, with teamwork and talking, we did find our way back to each other. Our daughter is now 7, and one day we’ll be able to laugh about our Diaper Genie cage match. Not quite yet, though.