A baby who wakes at night is not a baby with a problem
At six months about a third of infants wake their mother every single night. In one cohort of 388 infants, night waking had no measurable link to development or to the mother's mood. A larger cohort found one association, and this topic gives both.
Ask when babies sleep through the night and you will get a confident answer. The confidence comes from the fact that nobody agrees on what the question means.
A New Zealand study followed 75 typically developing infants, with parents keeping sleep diaries for six days every month for a year, checked against overnight video. The researchers used three different definitions of sleeping through.
| Definition used | Age at which half of infants met it | Not meeting it at 12 months |
|---|---|---|
| Asleep from midnight to 5am | 3 months | 11 of 75 infants |
| Eight hours in a row | 3 months | 11 of 75 infants |
| Asleep from 10pm to 6am, the hours a family actually keeps | 5 months | 21 of 75 infants |
Those counts work out at 14.7% and 28.0% (both percentages calculated by this guide from the counts the paper publishes). Same 75 babies, same night, and the failure rate doubles depending on which line you draw. The authors' own summary of the shape: The most rapid consolidation in infant sleep regulation occurs in the first 4 months.
A Canadian cohort of 388 infants asked mothers at 6 and 12 months, using either six or eight hours of uninterrupted sleep as the definition. Their result, stated as a range because the definitions and ages pull it around: Using a definition of either 6 or 8 hours of uninterrupted sleep, we found that 27.9% to 57.0% of 6- and 12-month-old infants did not sleep through the night.
And here is the finding that matters most in this whole stage. In that same cohort, sleeping through the night had no significant association with the infant's mental development, the infant's motor development, or the mother's mood, at the time or later. What it was associated with was breastfeeding: babies who slept through were much less likely to be breastfed.
The authors wrote: Considering that high proportions of infants did not sleep through the night and that no associations were found between uninterrupted sleep, mental or psychomotor development, and maternal mood, expectations for early sleep consolidation could be moderated.
A large American cohort of more than 1,200 infants, followed from 6 to 36 months, found two clear patterns. About 66% woke their mother roughly one night a week and stayed that way. About 34% were waking her seven nights a week at six months, dropping to two nights a week at fifteen months and one night by two years. Measures of the bond between infant and mother were not related to the waking.
"He wakes every night. Is there anything in that I should act on, or is that inside the normal range?"
"I am not sleeping. That is a separate question from whether the baby is."