Babies left to cry 'feel stressed', research finds Researchers measured the length of time they cried over successive nights, as their mothers waited in a nearby room. By the third night of the study, infants were found to have cried for a shorter period of time before falling asleep. But the study, published in the Journal of Early Development, found the levels of cortisol in their saliva remained high. In mothers, who could hear their babies, the level of the hormone fell in accordance with the time spent crying, indicating they had relaxed as the youngsters appeared to settle. The study found: "On the third day of the program, results showed that infants' physiological and behavioral responses were dissociated. They no longer expressed behavioral distress during the sleep transition but their cortisol levels were elevated. Wendy Middlemiss told the Daily Mail: "Although the infants exhibited no behavioural cue that they were experiencing distress at the transition to sleep, they continued to experience high levels of physiological distress, as reflected in their cortisol scores. Overall, outward displays of internal stress were extinguished by sleep training. However, given the continued presence of distress, infants were not learning how to internally manage their experiences of stress and discomfort. Researchers are now undertaking a longer study to test how the hormone level is affected as sleep patterns settle over more time. Dr Middlemiss is a member of the Attachment Parenting International Research Group, the Society for Research in Child Development, the National Council on Family Relations, and the American Psychological Association. Siobhan Freegard, of the parenting advice website Netmums, told the Daily Mail: "I don't think anybody would ever say that you shouldn't use controlled crying - it is about getting the balance right."