Eating In The Womb: When Does A Baby's Digestive System Mature?

Your baby's digestive system starts forming super early – often before you even know you're pregnant. While they won’t poop until after birth, they do pee in the womb and start building up their first bowel movement (aka meconium) along the way.

Once they have that first feeding, their system kicks into gear, ready to handle breastmilk or formula like a champ.

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Key Takeaways

• Your baby's digestive system begins to form by week 5 of pregnancy.
• Your baby doesn't eat in the womb, but they do process nutrients through the umbilical cord.
• Your baby's first poop after they're born is a substance called meconium, which builds up through pregnancy.

Do babies eat in the womb?

Babies don't "eat" in the womb in the traditional sense of the word, but they do absorb all the nutrients they need through the placenta. The placenta forms in the uterus during pregnancy and provides nutrients and oxygen to your baby through the umbilical cord.

The placenta also removes harmful waste and carbon dioxide from baby's blood. It produces hormones to help your baby grow, passes immunity from you to the baby, and protects the baby during pregnancy. In fact, the placenta acts as their lungs, kidneys, and liver until birth – keeping your baby alive and healthy during pregnancy.

Do babies poop in the womb?

While babies pee in the womb, they don't usually poop in the womb. Your baby's first bowel movement, called meconium, builds up in the intestines while you're still pregnant. Meconium is a thick, greenish-black substance made up of amniotic fluid, mucus, lanugo, bile, and cells that have been shed from your baby's skin and intestinal tract. Meconium usually stays in your baby's intestine until after birth, when they poop it out as the first bowel movement.

If your water breaks and you see dark green stains or streaks in the amniotic fluid, call your healthcare provider immediately. This is a sign meconium has gotten into the amniotic fluid, and baby could develop meconium aspiration syndrome (MAS), meaning they breathe meconium into their lungs before, during, or after delivery. The good news is most infants with MAS who receive treatment recover completely.

Your baby's digestive system in the womb

First trimester, conception to week 13

At 5 weeks, the embryonic period starts – when all of your baby's major systems and structures begin to develop. Their gastrointestinal tract starts to form and by week 9, all of your baby's essential organs have begun to grow. This includes their stomach, liver, kidneys, and pancreas. By 10 weeks, the anus and rectum form, the kidneys begin making urine, and the pancreas starts making insulin.

Also during week 10, your baby's intestines rotate and grow very quickly. From weeks 6 to 10, the intestines get longer and push out of the belly by the umbilical cord. But by week 12, the intestines typically go back into the belly.

Although your baby doesn't use their digestive system while they're in your uterus, by about 13 weeks of pregnancy they're already preparing for their first meal. At that point, they begin to swallow amniotic fluid.

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Want to track how your baby's organs are developing each week? The BabyCenter appOpens a new window gives you personalized, expert-backed updates – belly kicks and bowel prep included.

Second trimester, weeks 14 to 27

During weeks 15 to 18, your baby's liver and pancreas produce secretions. By the end of week 21, your baby can swallow. Their first bowel movement – meconium – is made in the intestinal tract.

Also during the second trimester, the digestive system is working, and your baby's sucking reflex is developing. And if their thumb happens to be near their mouth, they may latch onto it. After about 20 weeks, you may be able to catch a glimpse of them doing this during an ultrasound.

The wave-like movements that propel food along the digestive tract, known as peristalsis, begin between 14 and 23 weeks. Amniotic fluid is propelled from the stomach into the intestines by peristalsis. But just like with swallowing, it's only practice for your baby's system at this point because there's no actual food to move.

Third trimester, weeks 28 to 40

During the third trimester, your baby is getting more and more ready for birth and life outside the womb. At 30 weeks, their body begins absorbing minerals – such as calcium and iron – from the intestinal tract, preparing to take over from the placenta after birth.

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Most of your baby's development has finished at 31 weeks, and they'll start to rapidly gain weight for the remainder of your pregnancy. Finally, at 32 weeks pregnant, your baby's intestinal absorption reaches adult levels.

How to support your baby's digestive system development

What you eat and drink is the main source of nourishment for your baby. Folic acid, iron, calcium, vitamin D, DHA, and iodine play key roles in your baby's development during pregnancy. Eat a well-balanced diet and make sure your prenatal vitamin has iron, folic acid, and calcium in it. Talk to your healthcare provider to make sure you get enough calcium, vitamin D, DHA, and iodine.

Limit the amount of caffeine you drink, and avoid alcohol altogether. You'll also want to avoid raw meat and eggs, raw juice, unpasteurized cheeses, and processed meats to limit your risk of food-borne illnesses, which can be harmful for your baby.

Having a standard ultrasound exam around 18 to 22 weeks of pregnancy can tell your healthcare provider a lot about the health of your baby's digestive tract. For example, when the digestive system isn't developing properly, an ultrasound may show structural problems in the digestive system as well as abnormalities in amniotic fluid. If the ultrasound shows anything that concerns your provider, you'll most likely have additional tests – including a more detailed ultrasound – to find out more.

Key milestones in digestive system development

Weeks pregnant	Milestone
5 weeks	The digestive tube starts to form.
9 weeks	The stomach, esophagus, liver, and pancreas have begun to form.
7 to 10 weeks	Anus and rectum are formed after they separate from the urinary tract.
11 weeks	The abdominal wall starts closing and the intestines go back into the belly.
13 weeks	Your baby begins swallowing amniotic fluid, and meconium accumulates in the intestines.
14 weeks	Your baby practices sucking and chewing.
23 weeks	Peristalsis is happening, moving amniotic fluid through the digestive tract to practice for the real thing.
30 weeks	Your baby's body begins absorbing minerals from the intestinal tract.
32 weeks	Intestinal absorption reaches adult level.

Your baby may not be eating or pooping just yet, but their digestive system is already getting prepped for life outside the womb. From amniotic fluid practice to meconium buildup, everything's in motion for their first big meal – and first dirty diaper.

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