Sleep when the baby sleeps: almost nobody does, and the study says it is unlikely to fix it
After the second week, the authors report that fewer than half of women nap even once in a whole week, although one week in their own table sits just above half. By four months it is about one in four.
The same study that put monitors on the nights also counted the days. The women kept real-time sleep diaries alongside the wrist monitors. Naps were counted, week by week.
| Week after birth | Share of women who napped at least once that week | Average naps that week |
|---|---|---|
| 2 | 66.0% | 2.9 |
| 4 | 46.0% | 2.3 |
| 6 | 41.3% | 2.1 |
| 8 | 45.7% | 1.6 |
| 12 | 34.4% | 2.1 |
| 16 | 26.3% | 1.2 |
Read the left column as a running commentary on the advice. By six weeks, when most women are being told to sleep when the baby sleeps, fewer than half of them are managing it once in seven days. By four months it is about one in four. Among the women who did nap in a given week, the naps came to roughly 2.6 hours in total across that whole week.
And the authors add the part that is usually left out. Even if you did nap, they wrote, a brief daytime nap is unlikely to relieve the fragmentation of the night. The advice does not address the mechanism.
Now the other measurement. Ask women rather than monitor them and you get a different, lower number, and both are worth knowing.
Every woman who gave birth at one Norwegian hospital across a year was mailed a questionnaire at seven weeks. 2,830 replied, about two thirds of those contacted. Their average reported night sleep was 6.5 hours, their reported sleep efficiency was 73%, and 57.7% scored above the cut-off for a sleep problem on a standard questionnaire.
A second Norwegian cohort followed the same women from week 32 of pregnancy to eight weeks after birth and then to two years. Here is the distribution at eight weeks, which matters far more than any average.
| Norwegian cohort, percentages computed on all women answering at each point | Week 32 of pregnancy | 8 weeks after birth | 2 years after birth |
|---|---|---|---|
| Sleeping under 7 hours | 27.4% | 49.8% | 35.2% |
| Sleeping 7 to 8 hours | 31.4% | 29.8% | 45.1% |
| Sleeping 8 hours or more | 41.2% | 20.4% | 19.7% |
| Meeting a definition of insomnia | 60.8% | 59.6% | 40.8% |
Two things in that table are easy to miss. The first is that insomnia was already present in 60.8% of these women in late pregnancy, before the baby arrived. The second is that the two-year column is a two-year column. It is not a twelve-month figure and should not be read as one.
The same cohort separates two problems that get lumped together. Difficulty staying asleep rose from 2.93 to 4.24 days a week between pregnancy and eight weeks. Difficulty falling asleep fell, from 2.69 to 1.45 days a week. Falling asleep is not the problem. Staying asleep is.
Further into the year, a Canadian study followed 181 parents in 117 couples and asked them at 2, 4, 6 and 8 months. Averaged across both parents, reported night sleep was 6.4 hours at 2 months, 6.8 at 4 months, 6.7 at 6 months and 6.7 at 8 months. At two months, 59% were sleeping under 7 hours and 40% were inside the recommended 7 to 9 hour range; by four to eight months, between 53.6% and 55.3% were inside it. That sample was mostly white and highly educated, and the numbers are self-reported.
"My problem is that I wake up, not that I cannot fall asleep. Does that change what you would suggest?"
"Is there anything here worth checking for, or is this just what a broken night looks like?"