Baby not Gaining Enough Weight (Our Success Story + What Could be Wrong)

One of the first things you learn as a new mom is – if the poop is green, the baby is hungry. Despite my baby’s poop not being green since his first week at home, the first pediatrician checkup showed he only gained some 480g since coming home.

That’s when the sadness hit me. My baby was not gaining weight properly in his first month.

He should have gained at least 600g, and ideally, an entire kg. Naturally, the pediatrician suggested I start supplementing. Two of his meals a day were already made up of formula, but now I was to add it to the rest of his meals as well.

I didn’t like that, but whatever is best for him! Another checkup came along, and this time, despite the supplementation, my baby was still not gaining weight after 2 months. He only gained 300g. We were shocked, and so was the (different) pediatrician.

Our baby was not gaining weight but was feeding well + getting formula. So what was wrong?

Two weeks later, we finally figured out why he wasn’t gaining weight, and it turns out supplementing wasn’t the (only) issue. The doctor not listening to us was.

The Real Problem Behind my Baby not Gaining Enough Weight

At the first visit to our pediatrician, I mentioned to her my boy is spitting up a lot. Now, I know babies do spit up, and I know it’s normal.

But I was pretty sure the amount of milk coming out of my baby was not. In fact, I was pretty sure that my baby not gaining weight was at least in part due to his spitting up.

The doctor brushed it off – she probably thought we were overly worried as all first time parents are. What angered me later on, when it turned out that really was the biggest issue was – she wouldn’t even ask how much or how often he was spitting up. She just decided it didn’t matter and told us to start supplementing.

Now, he was already partially on formula (due to some breastfeeding mistakes I made), so I happily obliged – anything so he’s happy and developing. To be truthful, that was part of the issue, but we soon saw that there was no real progress still.

It wasn’t until one weekend he started screaming and arching his back, unable to nurse, that I realized the problem is much bigger than just my lack of milk.

Turns out, our baby was not gaining weight because of reflux – a serious case of reflux.

We called a free service helping new parents, and we got a simple advice: pump and feed him out of the bottle so he doesn’t swallow so much air (make sure you invest in a good bottle though – we use Dr. Brown’s anti-colic one and we’re super happy with it), and change the formula to the AR formulation (anti-reflux one). It’s a lot thicker so spitting it up becomes harder.

The result? He gained almost a pound (half a kg) in just a week. Over the next two, he did gain a whole pound – over half a kilo. And it made me both so relieved and so angry because it could have been solved so much sooner, and probably with less supplementing, if our pediatrician just wanted to hear us out.

Baby Not Gaining Weight: Causes & What to Do

Here’s what can cause baby not to gain weight, + my advice to all new parents struggling with their baby’s weight:

Triple check your milk supply before supplementing, if you think that’s the reason your baby is not gaining much weight.

Once you start supplementing, your milk supply regulates accordingly, meaning that it drops. That’s especially problematic during the first few weeks, when your body is learning how much milk your baby needs.

One way to know for sure is by investing in a good breast pump (there are some great ones covered by insurance).

Pump before a few feedings and you’ll get a pretty good idea of how much milk you have. If you see you do have enough milk, it means that’s probably not the issue.

But if you notice you still have a lot of leftover milk after your baby is done nursing, but your breasts don’t feel much lighter, it could also mean they’re not nursing efficiently, whether due to a poor latch of something else.

Your baby could be spitting up too much.

A bit of spit up after each meal is totally normal, but if your baby (like mine did) keeps spitting up until the next feeding, and they spit up copious amounts, be sure to look into it. Your babz may not be gaining weight because of reflux.

If you have enough milk and your baby isn’t spitting up (or vomiting), they may be ill. Take their body temperature and look for other signs of illness.

Don’t compete with other people’s babies.

If your baby is gaining enough weight but just isn’t on the chubby side, enjoy the fact that they’re healthy and don’t beat yourself up too much. A baby’s (normal) size says nothing about their health or you as a mother.

Finally, choose a pediatrician who’s dedicated to your baby’s health, and one you can trust. That way, you could avoid many problems that you simply don’t need to worry about on top of everything else.


A 27-year-old married mom, trying to have it all. I have a full-time job I enjoy, a home I’m in love with, and plenty of hobbies I try my best to have the time for. A psychologist by vocation, with the goal of helping young women live their best lives.

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