Cribsheet: A Data-Driven Guide to Better, More Relaxed Parenting, from Birth to Preschool (The ParentData Book 2)

by Emily Oster

The goal of the stay in the lab was to sleep train the infants. Nurses in the study collected data on the stress hormone cortisol in both the babies and their mothers, and were also responsible for putting the infants to sleep, and monitoring the sleep training. Before the sleep training each day, the babies’ and moms’ cortisol levels were tested and recorded. This was done again after the infant fell asleep. On the first day, the babies all cried. Their cortisol levels were the same before the training and after they fell asleep. Their mothers’ cortisol levels were also the same before the babies cried and after they were asleep. This was the same on the second day. On the third day, none of the infants cried (see above: sleep training works). However, they showed the same cortisol patterns: equal before bedtime and after they fell asleep. But for the moms, this changed: they had lower cortisol levels in the later period, when the babies weren’t crying. The authors suggested that this presents a problem with sleep training. In particular, they note that after sleep training, the mother’s stress levels do not stay in sync with the infant’s, which they interpret as possible evidence that the attachment between mother and infant is weakening. A number of commentators have argued that this is an overinterpretation of the study. For one thing, there is no baseline level of cortisol given, so we actually have no way to know if the babies were even experiencing elevated stress. ...