What Do We Know About Infant Sleep Problems?

Author: Ian St. James-Roberts, PhD, FBPsS

baby sleeping

Infants who cry a lot, or are awake and fussy at night are a source of concern for many parents. This part of the website, on infant sleeping, has two main sections to help parents with infant sleeping problems and questions.

This first section involves looking at the scientific evidence about the nature of infant sleeping problems and distinguishing these problems from crying problems. The second section aims to explain this evidence, so parents have some helpful guidelines for preventing infant sleeping problems and dealing with them if they already are occurring.

During the first 12 weeks after they are born, most infants go from short sleep and waking periods, which are spread fairly evenly over 24 hours, to longer periods of sleep during the night. By 3-4 months of age, around two thirds of infants are 'sleeping through the night' according to reports from parents, while one third continue to wake and cry out or otherwise get their parents' attention. Generally speaking, babies who continue to breast feed will keep waking in the night until an older age– a point I’ll come back to below. In any case, this is a remarkable achievement for most infants and an important and much anticipated developmental milestone for many parents. It is, however, a phase in a baby's life that is often misunderstood. Recent research has helped to explain this change in a baby's sleeping behavior and also revises some of the things experts thought or understood about infant sleep.

Until recently, infant crying and sleeping problems have been lumped together, but there is growing evidence that they are separate issues, with different causes. As described in the crying section, infant crying peaks around 4-6 weeks of age, with most crying occurring in the late afternoon and evening.

In contrast, infant sleeping problems, which usually involve babies waking up in the night, don't occur until after 3 months of age. So, sleeping problems occur in the night and at an older age than crying problems. Furthermore, recent studies have shown that infants who cry a lot in the first 4-6 weeks are not particularly likely to disturb their parents in the night at 3 months of age or have sleeping problems later.

Most babies wake in the night for feeding in the first few weeks after birth and most parents expect this. What concerns parents is when their baby continues to wake up at night after most other babies have stopped. This waking up at night does not usually involve a lot of crying. The chief sources of parental concern are (1) that their baby is behaving differently from most other babies in our society; and (2) that the baby being awake at night keeps the parents awake too and therefore disturbs the parents' own sleep.

The phrase "sleeping through the night" to describe these changes in an infant's night-time sleeping behavior is actually misleading. Child development studies using infra-red video-recording have found that almost all infants continue to wake in the night even if to the parent they seem to be sleeping all night. By 3 months of age, most babies begin to sleep for long periods or to fall back to sleep by themselves, without waking up their parents. The important question then is not why some babies fail to sleep through the night, but rather why nearly a third of infants continue to wake and disturb their parents in the night, while most infants stop doing so. Infants who continue to disturb parents at night are known as night-time 'signalers'

What, then, do we know about why some infants continue to be night-time ‘signalers’ while most infants stop doing this by 3-4 months of age?

First, and most importantly, several studies have shown that most infants who wake up and 'signal' their parents at night are healthy, put on weight and grow normally, and do not go on to have developmental problems - except for continuing to wake up and call out in the night. This conclusion is also supported by studies of prematurely-born infants. Because infants who are born early have a higher rate of neurological problems than full-term-born infants, these babies provide a test case for whether waking up at night is due to neurological disturbance. In fact, several large-scale studies have found low rates of night waking and signaling among infants who were born prematurely.

Second, we know that babies who are fed breast milk tend to continue waking and signaling at night until an older age than infants who are fed formula or mixed breast and formula milk. A common explanation is that breast-milk is digested more quickly in a baby’s stomach than other types of milk, leading the baby to continue to wake up hungry in the night. We do not know for certain whether that is correct, but it is generally accepted that breast milk is beneficial for infant development. Current medical guidelines are that babies should continue to be fed breast milk until 6 months of age, so parents who are doing that can expect that their baby may continue to wake and signal at night until that age as part of normal development.

Thirdly, and more controversially, there is evidence that parenting methods affect whether or not children wake and signal at night. Four separate studies have found that if parents follow simple steps in how they care for their babies, then their babies are more likely to stop signaling in the night by 12 weeks of age. These steps are described in the section, titled Preventing or Managing Infant Sleeping Problems. Before describing them, though, it is important to acknowledge that not all studies have found that these methods work, while some experts have expressed concerns that they may have unforeseen consequences. Until further research has resolved these issues, parents will need to use their judgment, as well as the scientific evidence, in choosing whether to adopt these forms of baby-care.

Infant and child night waking and signaling remains the main concern for parents, but other child sleep-waking problems begin to occur at older ages. Difficulties with getting toddlers and young children to settle to sleep (sometimes called bed-time 'struggles') become more common after about two years of age. Difficulties of this kind often occur together with night waking and signaling, but the two can occur separately. Although the evidence is weaker, bed-time struggles are thought to be partly due to how parents manage their children's bed-times.

In cases where infant night waking and signaling has become established as a serious and continuing problem, methods which change parenting practices can be effective in dealing with the problem. These methods, too, are described in the section titled, "Preventing or Managing Infant Sleeping Problems".

This section of the website was revised in December 2013 to include recent research evidence.