Let's assume bed-sharing is safe: so what?

All I really care about is what's best for moms

In my last post, I talked about how fragmented sleep is normal in most cultures. This is universally a fact of life for new mothers. I believe that part of a healthy postpartum journey involves recognizing that the temporary sleep deprivation we go through after a baby is born is normal (except in some extreme cases) and that we are going to be okay. It’s not going to shorten our lives or lead to chronic disease and, at some point, we will sleep through the night again. Nevertheless, when you are totally exhausted (as many mothers are) it’s normal to want to try to optimize what little sleep you are getting. What’s the best way to do that, according to research?

For some mothers, bed-sharing and side-lying breastfeeding might be the best solution, although this certainly doesn’t work for every mom. I am not going to dive into the relative risks of bedsharing here, except to briefly mention that as long as you follow the Safe Sleep Seven, the risk to your baby is lower than driving them in a car in a car seat (something that almost every parent inevitably chooses to do). I am also going to avoid any discussion of whether or not bed-sharing is good for your baby (in my research, I found that the claims seem quite disproportionate to the quality of evidence we have on this topic, at least so far). The only thing I am really interested in is: is bed-sharing good for moms?

As expected, there have been depressingly few quality studies on the topic. However, a 2022 large-scale meta-analysis of 6,472 participants from seven combined studies found that breastfeeding mothers slept more than non-breastfeeding mothers and co-sleeping, breastfeeding mothers slept the most of all. The difference was not massive - the mean sleep for breastfeeding mothers was 6.4 hours per night and for non-breastfeeding mothers it was 6.19 hours - but hey, I’d take the extra 20 minutes. Unfortunately, co-sleeping simply meant room-sharing in most of these studies, and there is no way of distinguishing between mothers who actually bed-shared versus those who had their babies in a crib in the same room. Nevertheless, the analysis was based on the highest-quality studies available that met rigorous inclusion criteria and controlled for many variables that have confounded other research. The reviewers conclude that the “literature on how co-sleeping disturbs maternal sleep is inconsistent according to the differences in methodology, sample size, and the definition of co-sleeping” (source).

The best individual study I could find on the topic of bedsharing and maternal sleep quality was a 1997 study by James McKenna et al. The aim of this study was specifically to measure bed-sharing versus non-bedsharing (in the same room). The study was done in a laboratory using polysomnography, instead of relying on self-reports. All infants were 11-15 weeks old at the time of research and all mothers were breastfeeding. The study also controlled for intentional versus reactive bedsharing by including some mothers who habitually bedshared and mothers who did not, and analyzing findings from each group separately. Each mother-infant dyad was measured for three consecutive nights of polysomnography, including a night where mothers did as they did at home (either bed-sharing or not), a night of bedsharing and a night of non-bedsharing. A total of 35 mother-infant pairs participated. Results showed surprisingly little difference in total sleep depending on sleeping arrangements or at-home sleeping habits. All mothers slept roughly 6.5 hours on all three nights (which is consistent with the research on hunter-gatherer mothers). Mothers who routinely bed-shared got the most total sleep of any group, specifically on the bed-sharing night, but due to the small size of the study, these findings were not significant (and the effect was not large). On the bed-sharing night, all mothers (regardless of how they slept at home) awoke more frequently, but were awake for shorter periods of time. Furthermore, mothers spent less time in Stage 3 and 4 deep sleep while bed-sharing and more time in Stage 1 and 2 lighter sleep, but again, the effects were very small (less than 4 % difference between groups). REM-stage sleep was the same in both groups.

What’s most fascinating to me about this study is the fact that despite relatively little difference in the total amount of sleep between the two groups, there was a major difference between the way the mothers felt in the morning. When mothers were asked to rate their sleep quality, 94% of the routinely bed-sharing mothers reported that they had slept enough during the night of bed-sharing, while only 33% of the mothers who typically slept separately reported the same. In other words, mothers who regularly bed-share claim that they are well-rested after a night of bed-sharing while mothers who do not regularly bed-share claim they feel terrible after a similar night. What’s most amazing is that this is true despite there being minimal differences between the two groups in terms of actual, measurable sleep metrics. How can this be?

My first thought when I read this was that bed-sharing and the technique of half-awake, side-lying breastfeeding is not something that a mother-and-baby dyad can learn in one night in a lab. Consistent with this hypothesis, a 1996 study by Milligan and team found that, for 20 postpartum women, nursing in the side-lying position was associated with significantly less fatigue, but required practice and instruction (source). Nevertheless, we’d expect that to show up in the data in some way, with routinely bed-sharing mothers clocking in significantly more sleep time or time in deep sleep or REM sleep on the bed-sharing night, compared with mothers who are not used to this way of sleeping. This was not the case.

It could also be that the group of routinely-bedsharing mothers in this study were in better health (although the study did try to control for this) or regularly engaged in other behaviors, like exercise and healthy eating, that helped them feel better on less sleep. I doubt it.

Perhaps it’s simply that, as I argued in my last post, it’s all in our head. What we feel constitutes a good night’s sleep is shaped by cultural norms and expectations. In the West, we expect a consolidated 7 or 8 hours, but this is simply not feasible when bed-sharing with an infant. We know that hunter-gatherers have highly-fragmented sleep (relative to most Westerners) and typically sleep only about 6.5 hours, but they generally report feeling well-rested in the morning, just like the bedsharing mothers. In a 2011 paper by Sarah Blunden et al, she argues that lack of consolidated sleep in infancy is often framed as a “sleep problem” in the West, necessitating behavioral training and intervention, with strong emphasis on a baby’s ability to “self-soothe” (source). Yet from a biological perspective, it’s completely normal for a baby to wake multiple times during the night to feed, and for this to continue through the first year and beyond. From the perspective of the hunter-gatherer mother, this does not pose any form of “sleep problem” for her or her baby. Western mothers who routinely bedshare may feel the same.

Another possible explanation is that mothers and babies who routinely bed-share and breastfeed learn to synchronize their sleep cycles (but again, this takes time and practice). Another study by James McKenna, from 1994, found exactly this. This study, also carried out in the sleep lab, was again quite small and recorded sleep from 8 mother-infant pairs using polysomnography. They found that “co-sleeping is associated with enhanced infant arousals and striking temporal overlap (synchronicity) in infant and maternal arousals, and that, possibly as a result, co-sleeping mothers and infants spend more time in the same sleep stage or awake condition.” In other words, when mothers and babies get into the habit of sleeping with one another, they awaken at roughly the same time and go back to sleep together. There is a natural synchronicity to human sleep, and so it makes sense to me that if a mother and baby are able to get into a rhythm with one another, mothers may feel better-rested despite the total number of arousals or total duration of sleep (source).

My final hypothesis is that mothers who routinely bed-share may have higher levels of circulating hormones that protect against sleep deprivation. I want to be clear that there is no solid evidence for this. There is research showing that new mothers are especially resilient to lack of sleep. A Canadian study of 20 mother-infant pairs tracked sleep quality, duration and fragmentation over the first 6 months of the baby’s life and found that “it did not appear to have the usual negative consequences to daytime functioning seen in other populations.” Mothers had more fragmented sleep than is typical, but reported feeling relatively well-rested and did not show the same signs of chronic fatigue that would have been expected in a population of non-mothers. The authors distinguish between sleepiness and fatigue: the former is defined as the desire to sleep more, or feeling like you need more sleep, while the latter is a state of physical and mental exhaustion that is more severe and typically associated with chronic stress and (in the long-term) disease. Mothers in the study had high levels of sleepiness but not fatigue (source). All mothers in the study were healthy, breastfeeding mothers who had delivered vaginally. Is it possible that the hormones released during breastfeeding have a protective effect against sleep deprivation? If so, we know that sleeping in close physical contact with your baby improves breastfeeding success and probably stimulates a higher release of these hormones, but could it also improve energy levels and perceived sleep quality? Unfortunately, we simply don’t have the research.

At the end of the day, all we can say for certain based on the existing evidence is that mothers who bed-share do not necessarily sleep better, but they claim to feel better. Why this might be the case is unknown. Are there any other benefits to bed-sharing for mothers? According to a review paper on infant sleep location and postpartum depression, there seems to be no clear relationship. Out of 5 studies, one study found that co-sleeping reduced maternal depressive symptoms, but the others found no relationship. Once again, the studies were not very high-quality and failed to distinguish between co-sleeping (having a crib in the parent’s room) and bed-sharing (source). I was similarly unable to find any research on the relationship between postpartum anxiety and infant sleep location (even though I feel strongly, based on personal experience and stories from other mothers, that there could be a relationship).

It’s worth noting that, for moms who don’t enjoy bed-sharing or co-sleeping, there is good data to suggest that gentle sleep-training is effective and can improve sleep, if done at an appropriate age. The best study we have on this is a randomized controlled trial carried out on 326 Australian children (source). At the time of the intervention, all of the parents of these children reported that they were struggling with sleep. The intervention did not begin until the babies in the study were older than 8 months old. Mothers in the intervention group received advice and information from a trained nurse on two sleep training techniques: “controlled crying,” in which the parent gradually extends the amount of time they allow a baby to cry and “camping out” whereby the parent stays with the baby by the crib until they fall asleep on their own. It was up to the parents which technique they chose to implement, but almost all of the parents in the intervention chose to try one or the other. The study tracked outcomes for both mothers and babies at 12 and 24 months of age and found that babies’ sleep in the control group had improved significantly, and maternal mental health had also improved slightly, though the effect was small (source). Most interestingly, in a follow-up of these children at age 6, the researchers found that there was no negative effect of the sleep-training intervention on children’s emotions and behaviors, psychological well-being, chronic stress, parent-child relationships, or parent-child attachment. The methodology used to assess these variables included a swab to check children’s cortisol levels and answers to a standardized questionnaire on parent-child relationships. Self-reporting is obviously less robust than objective measures, but I tend to trust parents’ assessment of their own children in these domains and I personally trust the results of this study.

Even if gentle sleep training starting at 7 months is indeed safe and effective, it doesn’t help moms during the first 7 months (by which time, most of us are back to work and dealing with the effects of chronic sleep deprivation). Many sleep training books insist that if a mother intends to sleep train, it’s important to start developing “good habits” early on in your sleep journey. By this they mean: don’t let the baby fall asleep on the boob, start teaching them to self-soothe and fall asleep unassisted in the crib as early as possible, get them on a schedule, and get them used to a consistent bed-time routine. Many mothers swear by this approach and I do not personally believe, based on the available evidence, that this does any harm to the baby. In fact, I am personally convinced that it will indeed make your journey easier if you fully intend to sleep train down the line. On the other hand, I think it’s also possible to bedshare with your baby early on - if that’s what helps you get the best sleep - and then switch to crib sleeping and sleep training later on if needed. In the Australian study referenced above, the parents who joined the trial had not yet implemented any kind of sleep training, and yet the intervention was still effective. In my personal experience, trying to get my babies on a schedule and implement “healthy sleep habits” only lead to more stress, frustration and anxiety. If I were to do it all again (which I probably won’t) I would let go of the pressure this created, and let my baby fall asleep on the breast in bed with me, simply because it was easy and felt natural. Then, when they reach an age appropriate for sleep training, I would reassess.

On the other hand, if you want to bed-share with your kids until they are teens, you’ll certainly face enormous stigma from anyone you dare admit it to in the West, but that’s what the hunter-gatherers did. In a study of the Aka tribe in central Congo, researchers asked people why they decided to sleep where they did and with whom. This is what they found:

“When asking Aka parents why children slept where they did, the standard answer was ‘this is where the child wants to sleep.’ For instance, a 12-year-old boy started the evening in a bakola home (mud hut), but got cold and decided to move back into his parents’ home. An 8-year-old girl who was sleeping next to her mother moved across camp to sleep with her father’s first wife because she said she loved her. In another case, an elderly grandmother was sleeping alone in her home and when asked why she was alone she said, ‘I prefer when the grandchildren sleep with me but they no longer come.’ This contrasts with a 10-year-old boy who said, ‘I prefer to sleep with my grandmother because I love her; she gives me a lot and takes good care of me.’ Another 6-year-old boy who shared a bed with his 9-year-old sister and parents said, ‘I love my mother so much I want to be next to her.’” (source).

This might sound like a nightmare to those who like to stretch out in a dark, quiet room, but to me it sounds beautiful.