A baby’s vital needs essentially break down into eating, sleeping, and pooping, and their only real form of communicating an issue with any of those things is through crying. But as any parent knows, identifying the fact that there is a problem is far, far easier than solving the problem, and as parents, that’s what we want to do. Now, if you’re the parent of a baby who’s learning to crawl, or who’s teething, or just figured out how to roll over, this may come as the least surprising scientific discovery imaginable, but developmental milestones are likely to cause disruptions in a baby’s sleep.

As a sleep consultant, the topic I get asked about the most is the 4 month regression. Parents can find it incredibly tough as baby starts to have more night wakes and do shorter naps. Many of us just think of sleep as an on-or-off situation. You’re either asleep or you’re not. But sleep actually has a number of different stages, and they make up the “sleep cycle,” which we go through several times a night. So in order to understand what’s happening to your baby during this stage, first you need to know a few things about sleep in general.

That right there might be the single most common question new parents ask. Is it a developmental milestone? A regression? Are they getting too much sleep during the day, or not enough? Maybe they’re just hungry. Maybe they’re too hot, or too cold. Let’s try to figure it out.