How and When Does a Baby’s Digestive System Develop?
Early Development in the Womb
- The digestive system begins forming very early in pregnancy. By the third week of gestation, the basic structures of the gastrointestinal (GI) tract start to develop 1.
- By five weeks, a tube forms from embryonic cells, which will become the baby’s digestive tract 2.
- By 8 weeks, the major organ systems-including the digestive system-have begun to develop 3.
- By the second trimester, the anatomical structures of the digestive system are in place, and the digestive tract continues to mature and practice its functions, such as swallowing amniotic fluid and producing digestive enzymes 4.
Note: The second trimester of pregnancy covers months 4, 5, and 6. It begins at week 13 or 14 and lasts through week 26 or 27 of pregnancy.
So, the second trimester includes the fourth, fifth, and sixth months of pregnancy
Here is a commonly used breakdown of pregnancy weeks by months, based on credible sources including BabyCenter, Flo Health, What to Expect, and others:
| Months of Pregnancy | Corresponding Weeks |
|---|---|
| Month 1 | Weeks 1 to 4 |
| Month 2 | Weeks 5 to 8 |
| Month 3 | Weeks 9 to 13 |
| Month 4 | Weeks 14 to 17 |
| Month 5 | Weeks 18 to 22 |
| Month 6 | Weeks 23 to 27 |
| Month 7 | Weeks 28 to 31 |
| Month 8 | Weeks 32 to 35 |
| Month 9 | Weeks 36 to 40 (or birth) |
Functional Maturation Before Birth
- Although the digestive organs are present, they are not fully functional during pregnancy. The placenta provides all nutrition and removes waste for the fetus until birth 5.
- The digestive system continues to mature throughout the second and third trimesters. While the anatomical differentiation of the intestine occurs by about 20 weeks gestation, functional maturation (such as organized peristalsis and the ability to coordinate sucking and swallowing) continues until around 29–34 weeks gestation 6.
At Birth and After
- At birth, a full-term baby’s digestive system is structurally complete and ready to start processing milk, but it is still functionally immature and continues to develop after birth 7.
- Breast milk or formula is the first food, providing easily digestible nutrients and supporting further digestive development 5.
- The digestive system gradually matures over the first months of life. By 6 to 9 months, a baby’s digestive system produces enough enzymes to begin digesting more complex foods, which is why pediatricians recommend introducing solids around this age 5.
- Full functional maturation of the digestive system, including the ability to process a wider variety of foods, continues throughout the first one to two years of life 5.
Summary Timeline
| Stage | Developmental Milestone |
| 3–5 weeks gestation | Digestive tract begins forming as a tube from embryonic cells 2. |
| 8 weeks gestation | Major digestive organs are present 4. |
| 20 weeks gestation | Anatomical differentiation of intestines 8. |
| 29–34 weeks gestation | Functional maturation: peristalsis, sucking, swallowing 8. |
| Birth | Structurally complete; starts processing milk 5. |
| 6–9 months | Produces more digestive enzymes; ready for solid foods 5. |
| 1–2 years | Ongoing maturation; handles a wider variety of foods 5. |
In summary:
A baby’s digestive system starts forming in the first weeks of pregnancy, is structurally complete by birth, but continues to mature functionally throughout infancy. It becomes capable of handling solid foods around 6–9 months and continues developing through the first two years of life 5.
Reference
1. Fetal development: your baby’s digestive system. BabyCentre UK. Published 2020. https://www.babycentre.co.uk/a25040502/fetal-development-your-babys-digestive-system
2. Bhatia A, Shatanof RA, Bordoni B. Embryology, Gastrointestinal. PubMed. Published 2020. https://www.ncbi.nlm.nih.gov/books/NBK537172/
3. What to Expect,Editors. Fetal Development: Baby’s Digestive System. What to Expect. Published October 7, 2014. https://www.whattoexpect.com/pregnancy/fetal-development/fetal-digestive-system/
4. What to Expect,Editors. Fetal Development: Baby’s Digestive System. What to Expect. Published October 7, 2014. https://www.whattoexpect.com/pregnancy/fetal-development/fetal-digestive-system/
5. When Do Babies’ Digestive Systems Mature Completely? MomJunction. Published April 6, 2020. https://www.momjunction.com/articles/when-do-babies-digestive-systems-mature_00602132/
6. Indrio F, Neu J, Pettoello-Mantovani M, et al. Development of the Gastrointestinal Tract in Newborns as a Challenge for an Appropriate Nutrition: a Narrative Review. Nutrients. 2022;14(7):1405. doi:https://doi.org/10.3390/nu14071405
7. Baby’s Digestive System – When and How it Develops. parenting.firstcry.com. https://parenting.firstcry.com/articles/babys-digestive-system-when-and-how-it-develops/
8. Indrio F, Neu J, Pettoello-Mantovani M, et al. Development of the Gastrointestinal Tract in Newborns as a Challenge for an Appropriate Nutrition: a Narrative Review. Nutrients. 2022;14(7):1405. doi:https://doi.org/10.3390/nu14071405
