The Fourth Trimester, and Why Your Newborn Isn't Broken

If you're in the thick of the newborn days right now, I want you to hear this first: your baby's sleep is not broken, and you are doing a great job!

The first three months of life are often called the "fourth trimester." Developmentally, your baby is still acting like they're meant to be inside the womb. That's not a cute phrase I'm using to make you feel better. It's actually how their nervous system works right now.

Here's what's going on under the surface:

Their nervous system is still immature. Newborns simply can't regulate sleep, hunger, or emotions well yet. That takes time.

They don't have a circadian rhythm yet. Babies don't develop a true day and night rhythm until around 12 weeks old. This is the biggest reason sleep feels so irregular in these early weeks. It's not something you're doing wrong.

They crave womb-like conditions. Being held, gentle movement, warmth, and sound aren't bad habits your baby is picking up. They're biologically normal needs, carried over from the last nine months.

They rely on you to co-regulate. In the womb, your baby was constantly regulated by your body: your temperature, your heartbeat, the sound of you, the motion of you moving through your day. After birth, they still need a caregiver to help them regulate. That's you, and it's exactly what you're supposed to be doing.

If the first weeks feel like survival mode, that's because in a lot of ways, they are. Your baby isn't fighting you or fighting sleep. They're adjusting to a whole new world outside your body, and that adjustment has a timeline of its own.

This is one of the reasons overnight postpartum support exists in the first place. Some families in Maine want someone there so they can actually sleep through a feed or two! Others just want a second set of hands during the hardest stretch of the evening. Either way, there's no version of the fourth trimester that you're supposed to figure out entirely on your own.

Next up in this series: why sleep feels so chaotic in these early weeks, and when that actually starts to change.

Talk soon!

Jillian Hollis