Scientists in Finland wanted to find out how babies' sleep patterns develop over the first two years of life. They also sought to determine how much these patterns vary while still falling within the boundaries of normal development.
The researchers collected survey data from parents of almost 5,700 babies. The parents answered questions about their child's sleep habits at ages 3, 6, 8, 12, 18, and 24 months, and whether they had concerns.
Here's what the researchers found, which they reported in the journal Sleep Medicine:
- Worrying is common. Throughout the study period, many parents said they were worried that their baby's sleep patterns weren't normal and that there might be something wrong. When their babies were 8 months old, for example, about 40 percent of parents had this fear.
- Normally developing babies have vastly different sleep patterns. Some babies slept through the night by 12 months, others still woke up a couple of times a night for 20 minutes. That's still within a normal range, according to the study.
- Over time, babies' sleep patterns stabilize. As they grew older, the babies slept longer at night without waking up, took less time to go back to sleep when they did wake up, and napped less during the day. By the time they were 2 years old, the children usually took just one daytime nap and woke up no more than once at night for a few minutes.
Nevertheless, some of the children did fall outside the average. Lead author Dr. Juulia Paavonen, of Helsinki University Hospital, in Finland, recommends that parents consult a healthcare provider if they're concerned about their baby's sleep patterns, especially if their child:
- Wakes up three times a night or more by 12 months old
- Takes more than 40 minutes to fall asleep or wakes up at night for an hour or longer by 8 months old
- Stays awake for more than 45 minutes at a time during the night by 12 months, or for more than a half hour by 18 months
For more information about baby sleep, including sleep training methods, night weaning, and baby sleep myths, visit our Baby Sleep Problems & Solutions page.
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