Babies need a lot of sleep. Some of them need as much as 16 hours a day, if naps are included. But even when they’ve made it to 12 months, nearly half cannot stay asleep for eight hours without waking. However, there’s no need for alarm: there’s a simple reason that babies can’t sleep through the night.
For sure, babies are born with an idea of time. They gain it from the womb’s rhythms and from mom’s distant heartbeat. But above all, they each inherit genes that control sleep. These genes are not something that the baby can ignore: all babies will sleep. They all also have another group of genetic instructions that will help them establish a circadian rhythm.
But that cycle will take time to develop, with the baby’s early days dominated by the simple urge to stay fed. Feeding wears the baby out, and each time that they sup on milk, they have to sleep it off. It will take time for the baby to develop something more complicated, and it may be as long as six months before they have a defined 24-hour day.
Nonetheless, the infant’s sleep does develop structure in those months, which helps their grasp of the difference between day and night grow too. This process can be boosted by giving baby some outside time during the day and keeping their room dark at night. They also need the prompt of cooler nights, so keeping the temperature a little lower in their sleeping room may help. And if they feed on breast milk, that will help them drop off.
No matter how hard parents work at it, though, there will always be babies who do not sleep through. A 2018 Canadian study in the medical journal Pediatrics found that as many as 43 percent of infants aged 12 months cannot sleep for eight hours in a row. However, it also found that moms with babies who don’t sleep through don’t suffer any more from depression than moms with good sleepers. And the reason for babies not sleeping all night? Well, they just can’t, and patience will inevitably be the only cure.