Cosleeping doesn't ruin your sleep.

There’s a story we tell exhausted new mothers. You know it if you’re a mother, but let me tell you just in case you’ve been living in a cave.

It usually goes like this: if you bring your baby into your bed, you’ll never sleep again.

You’ll spend your nights alert, anxious, barely resting. A sacrifice you’ll make for your baby at the expense of your own sanity.

It’s repeated so often it feels like fact. It’s passed from pediatricians to parenting books to well-meaning relatives standing in your kitchen man or woman-splaining how to take care of your baby.

There’s just one problem.

The research doesn’t support the tired tropes.

Dr. James McKenna has spent over four decades studying what actually happens — physiologically, neurologically, measurably — when mothers and babies sleep together. I’ve written about McKenna many times before, but if you’re unfamiliar, here’s the TLDR:

He founded the Mother-Baby Behavioral Sleep Laboratory at the University of Notre Dame, the only research facility in the world dedicated specifically to studying cosleeping, and has published over 140 peer-reviewed articles on the myriad facets of normal biological infant sleep.

In one of his landmark studies (Mosko, Richard & McKenna, 1997, PMID: 9143074, go read it yourself) researchers used polysomnography (the gold standard of sleep measurement, the same technology used in clinical sleep labs) to measure what actually happened to mothers’ brains and bodies on bedsharing nights versus solitary sleeping nights.

Total sleep time was not decreased on bedsharing nights. Not slightly decreased. Not meaningfully decreased. Not decreased at all.

REM sleep — the most restorative stage, the one responsible for emotional regulation, memory consolidation, and mood — was completely unaffected.

The researchers themselves described the total impact on maternal sleep as (and I’m quoting directly here) “modest.”

And then they said something the cultural conversation almost never mentions: those modest changes in sleep architecture were “adaptive.” Meaning the lighter, more responsive sleep of a bedsharing mother actually serves a function. It enhances her capacity to monitor her infant throughout the night.

The lighter sleep isn’t a side effect. It’s a feature honed through millennia of mother-baby sleep and it’s protective against the thing we fear most: SIDS.

This wasn’t an isolated finding. In a companion study published the same year in Pediatrics (PMID: 9240802), McKenna and colleagues found that bedsharing babies breastfed two to three times more frequently at night than solitary sleeping infants — without either mother or baby fully waking. The mother’s body and the baby’s body synchronized so completely that feeding happened almost invisibly, in the spaces between sleep stages, without the full arousal that characterizes a solitary sleeping baby’s night waking.

Magic, I know. Mothers are magic.

The baby fed more. The mother slept more. Both stayed in deeper relationship with each other’s rhythms throughout the night.

McKenna called this phenomenon breastsleeping, and argued it represented the biological norm for our species, practiced for all of human history, disrupted only in the last century and a half of Western industrialized life.

His 2005 review in Pediatric Respiratory Reviews (PMID: 15911459) went further still, arguing that the simplistic instruction “never sleep with your baby” was not just culturally biased but scientifically inaccurate and potentially harmful, because it pushed exhausted parents toward falling asleep with their babies on genuinely dangerous surfaces like sofas and armchairs rather than safely in a bed.

The irony is lost on none of us who work in normal biological infant sleep. The irony is, tragically, lost on virtually everyone consuming mainstream sleep discourse.

If this research has existed since 1997 — if polysomnographic studies have been measuring maternal sleep in bedsharing dyads for nearly thirty years — why does the cultural story remain unchanged?

Why are mothers still being told, in hospital discharge papers and pediatric waiting rooms and parenting forums, that bedsharing will wreck their sleep?

I think you already know the answer.

A mother who sleeps well with her baby close doesn’t need a SNOO. She doesn’t need a sleep consultant. She doesn’t need a subscription app or a weighted sleep sack or a course on wake windows.

She just needs her baby. And permission to trust what her body already knew.

A note on bedsharing safely:

McKenna’s research (and his colleagues, like Dr. Helen Ball, the world’s foremost researcher on SIDS) is clear that bedsharing safety is conditional. It depends on the absence of specific risk factors including smoking, alcohol, sedating medications, and unsafe sleep surfaces. The research supports informed, intentional bedsharing under safe conditions. It does not support unsafe sleep environments. If you want to explore safe bedsharing, McKenna has an entire book dedicated to it, and my dear friend and colleague Tiffany Belanger has tons of free resources via her platform @cosleepy.

The studies cited here are publicly available on PubMed. I encourage you to read them yourself. You can also go directly to The MotherBaby Sleep Laboratory’s Page to do a deep dive on the research McKenna has been conducting since before most of us were born. :-).