This is a great question. There are many documented physical, cognitive, and socio-emotional benefits to co-sleeping for at least the first year or two. To our current knowledge, long-term co-sleeping beyond that doesn’t seem to add benefit for cognitive or emotional development, but it does not harm it either (at least to the extent it has been studied).

In some cultures, children routinely sleep with their parent(s) until about puberty, and in those cultures, adolescence is when children begin sleeping alone. No evidence has been found for detriments to cognitive or emotional development in those cultures, although this practice is not usually researched where it is done routinely. In the US, studies of long-term co-sleeping are confounded with child sleep problems and our cultural bias against co-sleeping, and that is the main reason long-term co-sleeping has been studied so little. Even so, most US studies show no long-term negative effects of co-sleeping well into childhood.

The answer, of course, depends on what the parents want to do. Co-sleeping should cease as soon as the parent wants it to cease. If parents are happy with co-sleeping, it can continue as long as they wish, but in the US, most families end co-sleeping around age one or two years.

Developmentally, around the second birthday is a good age to transition a co-sleeping child into his/her own bed. The transition should include a clearly-established bedtime routine (probably one that was begun long before the transition) and consistent adherence to putting the child in his/her bed. At this age, there may be several nights of initial crying, but toddlers usually adjust quickly if they have a consistent history of co-sleeping. If the parents have not consistently co-slept, resistance to the transition may take longer because new research is showing inconsistency in sleeping arrangements may be more harmful than consistency regardless of where the child sleeps.

Many studies over the past 30 years have examined the beneficial effects of co-sleeping on infant development. The benefits, of course, depend on the safety of the co-sleeping environment – see James McKenna’s website about safe co-sleeping here:  https://cosleeping.nd.edu/safe-co-sleeping-guidelines/

Physiological benefits of co-sleeping safely include respiratory synchrony, different infant sleep patterns (fewer deep sleeps and more light wakes that may prevent Sudden Infant Death Syndrome), fewer episodes of infant apnea, increased breastfeeding, thermoregulation, lower stress hormones, and increased physical touch between parent and infant, among others. Cognitive benefits are generally not studied, but several studies have shown that co-sleeping infants were more independent as preschoolers or older children than solitary-sleeping infants. Emotional benefits of co-sleeping include greater attachment security, lower levels of stress hormones, and more positivity after stressful situations. Again, consistency is important and so is the parents’ positive attitude about co-sleeping.

I always tell parents the first rule of co-sleeping is … don’t co-sleep if you don't want to co-sleep. Some studies have shown a correlation between maternal depressive symptoms and co-sleeping, but with no clear cause and effect relationship, and other studies have not even found the relationship to exist.

My belief (and plan for future research) is that “reactive” co-sleeping (not wanting to but doing it out of desperation to get some sleep) may be harmful to mothers’ sleep and sense of well-being, while “intentional” co-sleeping (holding a parenting philosophy that embraces it and doing it safely because it feels right and is enjoyable) benefits mothers’ sleep and well-being. This idea has yet to be tested with research, but appears to me to explain why some mothers may not fare as well with co-sleeping as others, and why research doesn’t always find an effect. There are many dedicated resources to helping parents learn effective bedtime routines to help their babies sleep alone if that is what the parent wants.

If I understand this question, it seems to be asking about a parent who has experienced trauma and/or other issues and has also chosen (in part because of these issues) to continue co-sleeping. In this case, it may be the parent driving co-sleeping because of their own anxiety, and this would fall under “reactive” co-sleeping described in the question above. In research showing maternal depression correlated with co-sleeping, maternal anxiety is usually also present. Mothers with anxiety are more likely to have depressive symptoms or depression. In this case, the best solution would be for the parent to seek help for their anxiety from a mental health professional, which may lead to continued co-sleeping or not.

However, this question may also be asking about a child who has experienced trauma and the family may have chosen co-sleeping as a concrete way of helping the child build trust again or feel safe. In this case, the most important thing is the child feel consistently safe and cared for, and anecdotal evidence (but again, very little research evidence exists on this) suggests that children may use co-sleeping to feel safe and secure again. For example, it is not uncommon after a divorce for older children to want to sleep with their mother after a divorce, even if they have never co-slept. In the absence of research evidence about the effects of co-sleeping after trauma, it is my opinion that this can be an important way to help rebuild a sense of security in a child, if that is what the child and parent want to do.

I assume here this question is about sexual intimacy since intimacy through cuddling can easily be done with a child in the bed. For sex, try field trips. Seriously … taking “field trips” and finding another location to be intimate sometimes is probably good for any relationship (although I am not a Licensed/Registered Sex Therapist). Very little research has been done on the sex lives of co-sleepers, but since most families co-sleep at least occasionally during the first year, it does not seem to be a large problem. If the child begins the night in their own bed, then intimacy can occur before the child joins the parents in bed. Keep in mind that most families who co-slept have more than one child …

If you plan to have a “family bed” and all sleep together once the newborn arrives, the only change to be made is to have the older child begin sleeping on the other side of the non-pregnant parent.  Introducing changes a few months before the birth will help to ensure the older child does not resent the newborn for those changes. 

If the plan is for the older child to stop co-sleeping before the new baby arrives, around age two is a great age to introduce him/her to independent sleeping. While there may be some protest at first, typically it only takes about three nights of protest before a child aged two will begin sleeping independently. During the protest, let the child cry for five minutes, then go in and check on him lovingly and reassuringly, but quickly leave again even if the child is crying. Repeat every 10 minutes or so as necessary, if there is crying. Children aged two and older are much more age-appropriate for controlled crying than infants under one year of age.

My opinion, informed by my research and the existing literature on the topic, is that infants should sleep where the parent(s) are most comfortable with them sleeping. For some families, this is co-sleeping (bedsharing), as long as it is done in a safe way (see McKenna’s safe co-sleeping guidelines here: https://cosleeping.nd.edu/safe-co-sleeping-guidelines/ ).

For other families, that is putting the baby to sleep in a crib in the parent(s)’ room or in a different room. No health care provider should shame anyone for the legitimate, reasonable choices they make that work for themselves and their family. The fact is that the only theoretical training most physicians get is Learning Theory, which is focused on behavior as a result of rewards and punishments. Therefore, physicians tend to believe that if we “reward” infants by caving in to their “demands” (like co-sleeping or responding during nighttime distress), they will exhibit that behavior more often, as if they are trained in the same way dogs are. However, developmentalists like me have learned there are many more effective theories for understanding human development.

While learning theory has a place in understanding human behavior, it is not a developmental theory, and cannot explain why consistent responding to infant distress actually decreases infant crying, rather than increases it. Attachment theory can easily explain how that happens – consistent responses that are sensitive to the infant’s need (a need for contact and comfort is not a “want” during infancy, but a fundamental infant need) help the infant develop a secure attachment in which they know the parent is available when needed.

Guilty about not co-sleeping, or guilty about partner doing nighttime caretaking? Either way, make sure to “put on your own oxygen mask first” to make sure you can provide the baby with the best sensitive and responsive care you can. While I believe the evidence is clear that co-sleeping is not harmful for families who want to do it and do it safely, there is no evidence that failure to co-sleep harms children. There is also no evidence that one particular parent (over the other) is an optimal nighttime caretaker, as long as the nighttime caretaker is engaging in consistent sensitive and responsive caregiving that is age appropriate. As long as your partner is supportive of you and you are making caretaking decisions together, there is no reason to feel guilty.