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Your baby doesn't really need his digestive system until after he's born because all the nutrients he needs to grow and develop in the womb are delivered directly into his bloodstream through the placenta.
But just as soon as he has his first feeding after birth, his digestive system will begin processing food and excreting solid waste.
At 5 weeks of pregnancy, a layer of cells on the underside of your developing embryo rolls into a long tube that will become the digestive tract. Between 5 and 7 weeks, the tube solidifies until sometime between 8 and 10 weeks, when cells inside the tract create small spaces that expand to open up the tube again.
Parts of the digestive system
Your baby's primitive digestive system is made up of three main parts:
- The foregut, which becomes the esophagus, stomach, liver, and pancreas
- The midgut, which contains most of the small intestine and two-thirds of the large intestine
- The hindgut, which contains the rest of the large intestine, the rectum, and the anal canal
Foregut: esophagus, stomach, liver, and pancreas
Your baby’s stomach and esophagus start to form at about 7 weeks of pregnancy. The esophagus is the tube that moves food from your baby’s mouth to his stomach.
Around this time, the developing liver appears as a small outgrowth, and the pancreas also starts budding. These organs play supporting roles in digestion. The liver helps process many nutrients, aids in the digestion of fats, and filters out toxic substances like alcohol and drugs. The pancreas supplies digestive chemicals called enzymes that help break food into smaller particles.
The liver grows quickly at this time because it's needed to help form your baby’s blood. In fact, by 11 weeks, the liver accounts for 10 percent of your baby’s weight.
Midgut: The intestines
The intestines are the longest stretch of the digestive tract, and they grow very quickly. Because of the limited space in your baby's tiny abdomen, his intestines actually take up residence within the umbilical cord for a short time.
At 10 weeks, the small intestine starts folding into loops to create the huge surface area necessary to absorb nutrients from the food processed in the stomach. (On the inside, its lining also forms fingerlike projections called villi.) As the intestine folds, it also continues to lengthen, especially in the last trimester. By the time your baby is born, his small intestine would measure about 9 feet long if unfolded.
And that's not even its final size. By the time your child is an adult, his small intestine will be about 20 feet long!
At 12 weeks of pregnancy, the intestines start moving out of the temporary location in the umbilical cord and into the abdomen.
Hindgut: Rectum and anus
At first, your baby's rectum and anus develop together with structures that will form the bladder. But by 9 weeks of pregnancy, two separate regions develop: one for the urinary system and another for the anus and rectum, which form by 11 weeks.
Digestive prep: Practice makes perfect
Although your baby doesn't use his digestive system while he's in your uterus, by about 13 weeks of pregnancy he's already preparing for his first meal. At that point, he begins to swallow amniotic fluid, which he excretes through his urinary system. This swallowing practice helps maintain the right amount of amniotic fluid in the amniotic sac.
If there's too little amniotic fluid, it may mean the baby's urinary system isn't returning fluid to the amniotic sac. If there's too much fluid, it may mean the baby isn't swallowing enough and there are problems with the digestive tract.
At about 14 weeks, your baby also starts to make sucking and chewing movements. And if his thumb happens to be near his mouth, he may latch onto it. After about 20 weeks, you may be able to catch a glimpse of him doing this during an ultrasound exam.
The wave-like movements that propel food along the digestive tract (peristalsis) begin at about 23 weeks. As with swallowing, it's just practice for your baby's system at this point since there's no actual food to move.
Your baby's first bowel movement
At about the time your baby starts swallowing amniotic fluid, a substance called meconium begins to accumulate in his intestines. Meconium is made up of amniotic fluid, mucus, skin cells, and other substances your baby has swallowed in utero. Meconium stays in your baby's intestine until after birth, when it is eliminated as his first bowel movement.
What you can do during pregnancy
Having a standard ultrasound exam around 18 to 22 weeks of pregnancy can tell your health care 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
|5 weeks||The digestive tube starts to form.|
|7 weeks||The stomach, esophagus, liver, and pancreas start to form.|
|8-10 weeks||Cells inside digestive tube hollow it out.|
|8-12 weeks||Intestine grows in length and is housed in the umbilical cord.|
|11 weeks||The rectum and anus form.|
|12 weeks||Intestine leaves the umbilical cord and returns to the abdomen.|
|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.|