A study published last month in the journal Sleep Medicine is the largest and best-designed study to investigate this question.
The study followed 153 middle-class Israeli families, all consisting of married couples having their first baby. Sleep was evaluated in the mothers in the third trimester of pregnancy and again in both mothers and babies at 3 months and 6 months postpartum.
The moms and babies wore actigraphs for 5 nights in a row at each time point, and the mothers also kept sleep diaries for each night. I do not understand why, in 2015, researchers don’t care more about fathers’ sleep, but it wasn’t even considered in this study.
The families in this study weren’t advised where their babies should sleep, they each made their own choices. At 3 months, most babies (76%) were sleeping in their parents’ room. At this age, 58% of infants were fully breastfed and 25% were partially breastfed. At 6 months, 50% were roomsharing; 32% were fully breastfed, and 28% were partially breastfed.
The roomsharing moms had more fragmented sleep than those whose babies slept in a separate room. They didn’t sleep less overall, both groups of moms had an average nighttime sleep of just under 6.5 hours, but roomsharing moms woke more often and spent more time awake during the night. Their longest uninterrupted sleep period during the night was on average 2 hours and 20 minutes at both 3 and 6 months, compared with about 2 hours and 47 minutes in the moms who didn’t roomshare. Again, this difference was found after accounting for the effects of breastfeeding or formula-feeding on sleep.
In the study, roomsharing or sleeping in a different room actually didn’t seem to affect the babies’ sleep as measured by the actigraphs. However, when babies slept separately, their moms weren’t aware of some of their wakings. That is, the actigraph recorded some wakings that weren’t noticed by the moms, so the babies must have put themselves back to sleep without calling for help from a parent in the next room. With roomsharing, those wakings are more likely to wake the mother and disrupt her sleep.
One of the big limitations of this study was that it didn’t ask moms why they chose their sleep arrangements. However, roomsharing or not wasn’t related to the babies’ sleep patterns so was most likely driven by maternal preference. Supporting that, the moms who had a harder time sleeping in pregnancy and at 3 months were more likely to roomshare at 6 months. We have no way of knowing if the roomsharing moms would actually sleep better if their babies were in a separate room.
Maybe they made that choice because it was the best way for them to sleep. Maybe putting their babies in a separate room would have caused more anxiety and interfered with their sleep in some other way. Sleep is very personal, and where a baby sleeps in a complex decision.