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Letting babies "cry it out" does not affect behaviour in later life, reports study

Tuesday 17 March 2020

"Leaving babies to cry it out won't do them any harm", reports the Metro, while The Guardian's coverage led with the headline: "Should you let babies 'cry it out'? Debate reignited by new study".

The debate about whether parents should quickly respond to crying babies, or leave them to cry (often called controlled crying), has rumbled on for decades.

Some experts fear that leaving babies to cry causes them stress and could damage a child's attachment to its mother, or cause behavioural problems. Others claim that responding too soon means babies cry more and do not get a chance to learn to soothe themselves.

A new study, which has prompted these media headlines, suggests that leaving babies to "cry it out" occasionally does not have negative effects on future crying, a baby's attachment to its mother, or the child's future behaviour.

If anything, young babies left to "cry it out" from birth to 3 months of age tended to cry less by the age of 18 months. However, few mothers left their newborn babies to cry often, so this finding may be less reliable.

The researchers say their findings do not support either the advice to leave babies to cry or to respond quickly. Instead, they say the study supports parents to be intuitive and adapt their style as their baby grows.

Where did the story come from?

The researchers who carried out the study were from the University of Warwick. The study was funded by the Health Foundation and published in the peer-reviewed Journal of Child Psychology and Psychiatry. It is free to read online.

The UK media reports were mostly accurate and balanced. The coverage by The Guardian was the only one to make the point that few mothers in the study often left their baby to cry it out when they were a newborn. The Mail Online headline, "Letting babies 'cry it out' at night helps to soothe them...", overstates the findings. We do not know whether letting babies cry helps them learn to soothe themselves or not. Also, the study looked at daytime crying, as well as night.

What kind of research was this?

This was a cohort study. Cohort studies are useful ways to look for links between risk factors (such as crying it out techniques) and outcomes (such as behavioural problems or amount of crying in later life). However, they cannot prove that a risk factor directly causes an outcome. Other factors may be involved.

What did the research involve?

Researchers recruited 178 newborn infants and their caretakers from 3 hospitals in the east of England. The cohort was originally set up to compare babies born very prematurely, or with a low birth weight, to those born at term, so 73 of the 178 babies in the study were born before 32 weeks or weighed less than 1.5kg at birth. Previous studies had shown no difference in crying behaviour between the groups, so all the babies were included in this study.

Mothers were asked to report on how often their babies cried, and for how long, straight after birth, at 3 months, and at 18 months. They were also asked how often they let babies "cry it out" when they were a newborn, 3 months, 6 months and 18 months.

Responses were recorded as no crying it out (once or never), a few times, and often.

When the babies were 18 months old, they and their mother were assessed for the strength of their attachment (using the Strange Situation Procedure) and for the baby's behaviour (using the Play Observation Scheme and Emotion Rating and the Tester's Rating of Infant Behaviour). Mothers were also asked to rate their child's behaviour (using the Child Behaviour and Health Questionnaire).

A mother's sensitivity to their baby's, meaning their perceived ability to recognise and respond to their baby's behaviour, was rated at 3 and 18 months using the Mother-Infant Structured Play Assessment.

Researchers looked to see whether mothers' reports of how often they let babies cry it out were linked to their scores in the behavioural, attachment or sensitivity tests. They also looked to see whether letting babies cry it out was linked to length or frequency of crying at future measurement points.

They took account of the following potentially confounding factors:

  • parental income
  • premature birth
  • whether the baby was their firstborn child

What were the basic results?

Few mothers reported leaving their baby to cry it out often when they were a newborn, but use of this technique increased as the child got older:

  • 29.1% let babies cry it out a few times when they were a newborn, and 7.6% let them do it often
  • 48.9% let babies cry it out a few times when they were 3 months old, and let them do it 12.9% often
  • 52.1% let babies cry it out a few times then they were 6 months old, and let them do it 7.8% often

Attachment between mother and baby and the baby's behavioural development at 18 months were not linked to how often mothers had let babies cry it out. Mothers who let babies cry it out were equally sensitive to their babies at 3 months, and those who let them cry it out at 18 months were more sensitive than those who did not.

Babies who had been left to cry it out a few times or often when a newborn were found to cry for shorter periods at age 18 months. The study does not report how much shorter the crying periods were, so it is hard to tell whether this is a major difference.

There were no other links between how often babies were left to cry it out, and duration or frequency of crying.

How did the researchers interpret the results?

The researchers said: "Whether contemporary parents respond immediately or leave their infant to cry it out a few times or often might not be associated with short- or long-term adverse effects on infant behaviour or quality of infant-mother relationship during the first 18 months in this UK sample."

They added: "We neither recommend leaving infant to cry out, nor responding immediately. Rather, our findings are consistent with an approach to parenting that is intuitive and adapts to infant demands according to infant regulatory competencies [the ability of the baby to soothe itself] across infancy."


How best to deal with a crying baby has been questioned by parents and parenting advisors for many years. This study suggests that a strict regime of either ignoring crying or responding immediately is neither necessary nor widely used. Most parents in the study responded more quickly when babies were a newborn and adapted to leaving them for longer as they grew.

Importantly, leaving babies to cry sometimes did not seem to have a negative consequence for their later behaviour or development. This may be reassuring to parents who worry about harming their children by leaving them to cry some of the time.

The study design means we cannot tell whether leaving babies to cry it out directly caused the reduction in crying time seen at 18 months. Many other factors could have been involved in this.

There are limitations with the study. The researchers relied on mothers accurately describing how long and how often babies cried, and their own response. The study is relatively small, so groups with less common behaviour, such as those who left their babies to cry it out often when they were a newborn, are very small. This means the results may be less reliable for these groups. Also, because the study included many babies who were born prematurely or with low birth weight, the group is not necessarily representative of most babies.

There are many reasons why a baby might cry, and lots of things you can try to settle them. Dealing with a constantly crying baby can be exhausting and distressing.

Get more advice on how to soothe a crying baby.

Analysis by Bazian
Edited by NHS Website