Do Prenatal Vitamins Make You Gain Weight? What's Actually Happening (and What Isn't)

If you've noticed the number on the scale shifting after starting a prenatal, you're not imagining things. And you're definitely not alone.

Weight changes during the trying-to-conceive and pregnancy stages can feel confusing, especially when you're already juggling so much. The good news? Prenatal vitamins themselves are very unlikely to be the reason. There's more to the story, and we're here to walk you through it.

The short answer is: probably not. Prenatal vitamins contain nutrients like Folic Acid, Iron, Choline, and DHA, not meaningful calories. A daily prenatal pack has virtually zero calories.

So why does weight gain on prenatal vitamins feel real? It usually comes down to timing.

Most people  start prenatal care around the same time their body begins to shift, whether in early pregnancy or while preparing to conceive. Hormonal changes, increased blood volume, and fluid fluctuations are already underway, and the prenatal gets the blame because it showed up at the same time. What you're likely noticing is water retention: your body holding onto extra fluid in response to hormonal shifts. This kind of change is temporary and can fluctuate noticeably within days. Fat gain, by contrast, is a much slower process that requires a consistent calorie surplus over time, something your prenatal (with virtually zero calories) simply can't cause.

Progesterone (one of the key hormones in conception and pregnancy) rises after ovulation each cycle, whether or not you conceive. (Here's a closer look at  how your hormones shift throughout your cycle). Its job is to prepare the uterine lining for a potential pregnancy, and that preparation comes with side effects: slower digestion, water retention, and bloating. During the luteal phase alone, it's common to see a 1 to 3-pound shift on the scale from fluid retention.

When you're actively trying to conceive and paying closer attention to your cycle, you may notice these fluctuations more than you did before. During pregnancy, progesterone climbs even higher, which is why the effects can intensify. Either way, the water retention is driven by your hormones, not your vitamins.

Bloating is one of the more common side effects of prenatal vitamins, usually tied to one ingredient: Iron.

Iron supports red blood cell production and oxygen delivery to a developing baby. It's an important nutrient when you're trying to conceive and during pregnancy, but it can slow digestion, leading to constipation, gas, and that "puffy" feeling. Not all forms of Iron affect your body the same way. Iron salts like ferrous sulfate, ferrous fumarate, and ferrous gluconate tend to be harder on digestion. Chelated forms like ferrous bisglycinate (the form used in Bird&Be's prenatals) are designed to be more bioavailable and gentler on your stomach.

How to ease prenatal bloating

A few small shifts can help:

• Take your prenatal with food

• Drink plenty of water throughout the day

• Add fiber-rich foods like oats, beans, and vegetables

• Try a different time of day for your vitamins 

If bloating sticks around, talk to your healthcare provider. Iron is in a separate capsule across all Bird&Be prenatal formulas, so you can temporarily set it aside if it's causing discomfort. The Gentle Prenatal Pack was designed with sensitive stomachs in mind, and for those who prefer not to swallow capsules, the Gentle Prenatal Gummies are a vegan, Iron-free alternative.

Some people notice shifts in their appetite when they start taking prenatal vitamins. Iron and certain B vitamins can cause nausea on an empty stomach, which may lead you to eat more (or less) than usual.

This isn't the prenatal changing your metabolism. It's a digestive response, and eating smaller, more frequent meals often helps.

During pregnancy, your calorie needs naturally increase, particularly in the second and third trimesters. Your appetite may genuinely grow because your body is asking for what it needs. The prenatal supports this process; it doesn't drive it.

Side effects of prenatal vitamins tend to be mild and digestive. Here's what you may notice:

• Nausea, particularly when taken without food

• Constipation, usually from Iron

• Bloating or gas

• A metallic taste in the mouth

These often improve after the first few weeks. If they don't, switching formulations may help.

Bird&Be's Complete Prenatal Pack uses bioavailable (A.K.A. ready for your body to absorb) forms of key nutrients, which can help reduce discomfort. If you're trying to conceive, the Female Fertility Power Prenatal Pack combines your prenatal with antioxidants like CoQ10 and NAC in one daily packet.

Your body is doing incredible work. A few habits can help you feel more at ease:

• Stay hydrated. Water supports digestion and can ease water retention.

• Move your body. A gentle walk after meals can help with bloating.

• Talk to your provider if you're concerned about weight gain from prenatal vitamins.

Weight changes during the fertility journey are real, and so are your feelings about them. What matters most is that you're giving your body what it needs.

Do prenatal vitamins make you gain weight? On their own, no. They're here to help, and so are we. Take the Bird&Be quiz to find the prenatal that fits your body and your journey.