'Sleeping through forever': The sleep training lie

In the early days of motherhood, their is a certain obsession with sleep. Unlike most new mother obsessions, the obsessions seems to be encouraged by others who suggest that if you do not get your child sleeping through as a baby they will be cursed with sleeping difficulties for the rest of their lives. Inversely, the sales pitch for sleep training appears to be that you will never have to wake up at night again.
I know a number of mothers of what are now toddlers, who are quite exasperated to find that this is not the case. With 20 - 40% of children being reported to have sleep difficulties 3 they are clearly not alone.
So why do kids wake up at night and can you sleep train your way out of it.

Causes of sleep problems

• Biological:  Babies and toddlers have immature neural and circadian mechanisms that make them unable to sleep through the night or self-settle. This ability develops naturally, over the first few years of life.1. 
• Temperament
• Genetics: Children with poor sleep are often the children of insomniac parents, particularly for boys 2.
• Environmental: Poor sleepers tended to have more noise or light in the room where they sleep 2.
• Stress: Poor sleepers tend to have more environmental stress factors 4.
• Anxiety: Poor sleepers tend to have more nightmares than children who slept well 2. Onset of sleep problems was also found to be related to more fears and a need for reassurance and caregiver proximity 3.
• Co-sleeping: Co-sleepers are noted to have more sleep problems than no co-sleepers 4.
• Inconsistent or inappropriate bedtime for age 1
• Being allowed to wake later: Children who delay sleep onset and resist bedtime tend to wake later, this suggests a sleep phase delay which may maintain pre-existing problems 3.
• Parental difficulty in enforcing bedtime limits e.g.responding to multiple requests for attention after bedtime 1.
• Sleep onset associations: The child relies on the association present at the time of falling asleep e.g. parental presence and is unable to recreate this alone. They then require parental assistance (by crying, calling out or getting out of bed) to assist them to get back to sleep 1.
• Medical issues
• Developmental changes: Sleep problems often occur for a short period of time due to normal physical, cognitive and emotional changes occurring at various developmental stages 1.

Sleep problems are usually caused by more than one factor. As with sleep problems in adults, a sleep problem usually results from a genetic or biological predisposition that is triggered by a precipitating factor (e.g. a developmental or environmental change) and then perpetuated via behavioural or environmental issues 1.
Certainly, past sleep difficulties do seem to be predictive of future problems 6. One study found that 41% of children with a sleep problem at 8 months of age still had a problem at 3 while only 26% without a problem at 8 months had a problem at 3 4. Another study found that 84% of children who had sleep disturbances at between 15 and 48 months still had sleep difficulties 3 years later 5.
The issue of whether sleep training can totally resolve this issue however is difficult to determine. Studies on sleep training methods have very good results. There is a higher and more rapid resolution of problems compared to those with no intervention and this result is sustained in the majority of participants for at least six months. However few studies provide follow up for longer than six months and even less have follow up for more than a year 1. As such at this point it is impossible to make claims about the long term success of sleep training.
I would hypothesise that for children who are predisposed to sleep difficulties, it is a continual process of retraining the child to sleep as they encounter factors that create sleep disturbances.