How Breastfeeding Shrinks Your Uterus & Why That’s a Good Thing

What Happens to Your Uterus After Birth?

Many new moms don’t realize how breastfeeding shrinks the uterus and supports faster recovery. Right after you deliver your baby (and the placenta), your uterus starts shrinking back to its pre-pregnancy size. This process is called uterine involution. Basically, your uterus, which grew to the size of a watermelon, is working its way back down to the size of a pear.

It doesn’t happen overnight. For most people, this process takes about six to ten weeks. Some days, you might feel cramping—that’s your uterus doing its job. Think of it like a slow and steady “reset.”

Your healthcare provider may measure something called your fundal height in the hospital—this is just how high your uterus sits in your abdomen. A steadily lowering fundus is a good sign that things are moving in the right direction.

Around two days after delivery, your uterus is typically the size it was at 18 weeks of pregnancy. A week after birth, it’s about the size it was at 12 weeks. By six to ten weeks, it should return to its original size—roughly as big as a closed fist.

How Breastfeeding Helps Your Uterus Shrink

The Role Of Oxytocin

Here’s where breastfeeding comes in. Every time your baby latches and suckles, your body releases a hormone called oxytocin. Oxytocin is sometimes called the “love hormone” because it helps you bond with your baby—but it also causes your uterus to contract.

These contractions help your uterus shrink down. They might feel like mild cramps (or sometimes pretty intense ones, especially if this isn’t your first baby). They’re often called afterpains, and while they’re not fun, they’re actually a sign that your body is healing.

Some mothers describe a tingling or tightening feeling in their breasts as milk lets down—this is also triggered by oxytocin. That same hormone works double duty, triggering both milk flow and uterine contractions.

Proven Recovery Benefits

Breastfeeding regularly—especially in the first few days after birth—can:

• Trigger those helpful uterine contractions
• Reduce postpartum bleeding faster
• Speed up your uterus returning to its pre-pregnancy size

What Research Says About How Breastfeeding Shrinks the Uterus

One study measured fundal height on Day 1, Day 3, and Day 7 after delivery. The breastfeeding group had a steeper decrease in fundal height—meaning their uterus was shrinking faster.

According to a study, the uterus of non-breastfeeding mothers may remain slightly enlarged compared to those who breastfeed. That’s a big reminder of how powerful breastfeeding can be—for you, not just your baby.

While not every single study shows dramatic results, the overall pattern is clear: breastfeeding supports the natural healing process. And the sooner you start, the better the results tend to be.

Why It Matters For Your Recovery

Shrinking your uterus faster isn’t just a fun fact—it can make a real difference in how you feel.

• You may bleed less and for a shorter time.
• You might feel stronger and more “put back together” sooner.
• You’re reducing your risk of complications like subinvolution (when the uterus doesn’t shrink properly).

A Safety Boost

It’s also a safety issue. After the placenta is delivered, your uterus needs to contract to close off the blood vessels that fed it. If this doesn’t happen, you risk excessive bleeding. Breastfeeding promotes those strong contractions through oxytocin, which helps close off those vessels quickly and safely.

The oxytocin that comes from breastfeeding doesn’t just help your uterus shrink—it can help reduce stress and promote emotional bonding with your baby. That’s a win-win when your hormones are doing acrobatics.

For Faster Postpartum Healing…

Here are a few doable tips:

• Start breastfeeding early. Try to breastfeed within the first hour after birth if possible. That first latch can kickstart oxytocin production.
• Nurse frequently. Newborns eat often—use that to your advantage.
• Stay hydrated. Drinking plenty of fluids helps with milk supply and healing.
• Keep taking your prenatal vitamins. They’re still useful during recovery.
• Do lots of Skin-to-skin. Skin-to-skin contact supports oxytocin release.

Every feed counts. Even partial breastfeeding can provide oxytocin boosts that help your uterus do its job.

What If Breastfeeding Doesn’t Work For You?

Not everyone can or chooses to breastfeed, and that’s okay—your uterus will still shrink, just at its own pace. Gentle belly massage (only if recommended by your provider), walking, and staying hydrated all help.

Doctors sometimes give synthetic oxytocin or perform a uterine massage after delivery if contractions aren’t strong enough. These are tools to help your uterus do what it needs to do—just like breastfeeding does naturally.

You’re not failing if you can’t breastfeed. Recovery looks different for everyone. What matters most is that you’re supported, informed, and taking care of yourself however you can.

The Bottom Line

Breastfeeding doesn’t just nourish your baby—it helps heal your body. Every time you breastfeed, you’re helping your uterus contract and shrink back to its pre-baby shape. That’s real, measurable recovery happening inside you.

If you need help getting started with breastfeeding or have questions about what’s normal, don’t wait. Reach out to a lactation consultant or talk to your care team. You’ve got this—and you’re not alone.

Resources

• Find a breastfeeding support group near you.
• Milkology Breastfeeding Class – Affordable, video-based online course to help you master breastfeeding at your own pace.

References

1. Chua S, Arulkumaran S, Lim I, et al. Influence of breastfeeding and nipple stimulation on postpartum uterine activity. Br J Obstet Gynaecol. 1994.
2. StatPearls. Physiology, Postpartum Changes. National Library of Medicine. Updated 2022.
3. Amelia R, Masrul, Sriyanti. The Effect of Breastfeeding on the Uterine Involution Post Partum Mothers. World Journal of Research and Review. 2019.
4. Cleveland Clinic. Uterus Involution: Causes, Process & How It Feels.