How Does a Baby's Stomach Grow?

Your baby's stomach grows by leaps and bounds during the first days of life. Learn how it happens so that you can verify that your breastfeeding is sufficient.
How Does a Baby's Stomach Grow?

Last update: 26 March, 2022

Consultations about the growth of a baby’s stomach are very frequent during a child’s first medical check-ups. This aspect of newborn health is related to questions about breastfeeding: Is the milk I produce enough? Is my baby hungry? How much milk do I have to offer you? If you’re the mother of a small baby, this article may interest you. Keep reading!

A baby’s stomach

The stomach is a hollow organ that makes up part of the digestive tract. It not only fulfills the function of temporarily housing food but is also responsible for the digestion and absorption of essential nutrients.

For more than a century, researchers have studied newborn babies in order to determine the size of their stomachs and thus estimate the amount of milk they can tolerate in one feeding.

Representative models of a baby’s stomach

Based on the research data, different representative models of the growth of the baby’s stomach have been created. These reflect the changes in the different stages of the first month of life.

The objective of these models is to facilitate visual representation, as part of an educational strategy for families. The most common is called “Belly balls”. Both its original version and its modifications are available on the internet.

In any case, these models shouldn’t be taken at face value when indicating the amount of milk you should give your baby.

On the one hand, because anatomical or structural capacity is a static measure, which could be applied to rigid containers (such as the shell of an egg), but not to a compliant organ such as the stomach.

Based on this point, it’s more appropriate to focus on the stomach’s physiological (or functional) capacity. This refers to the volume that said organ can tolerate after stretching its walls, without causing discomfort or pain (Scammon, 1920).

On the other hand, the most recent research has shown that the size of the stomach at birth is related to the gestational age and birth weight of the child. Therefore, this measure varies according to each case.

A baby holding a bottle.

The evolution of the baby’s stomach growth

Inside the maternal uterus, the baby ingests quantities of amniotic fluid and, in this way, activates the mechanisms of maturation of the digestive tract.

At birth, it slowly empties that content and makes room for maternal colostrum. We don’t know exactly what the mechanisms are that are responsible for these changes, but it’s presumed that some hormones and nutrients present in milk could be the necessary stimuli for the growth and functional maturation of the stomach.

Next, we’ll explain in detail how the newborn’s stomach develops.

The first day of life

There’s great controversy about the capacity of the stomach at birth, which is related to the amount of milk that’s necessary to offer the baby in the first hours of life. Especially when feeding formula milk.

According to studies conducted in the last decade, gastric capacity at birth is approximately 20 milliliters per cubic centimeter (Bergman NJ, 2013). Other studies indicate that when volumes of 30 to 35 milliliters per cubic centimeter are reached, the pressure generated within the stomach is capable of producing discomfort and pain (Zangen S, 2001).

However, it’s important to reinforce the idea that these findings don’t imply that the volume of milk to be offered is 20 milliliters. There are other variables, such as birth weight or gestational age, that determine the amount of milk that each baby can tolerate.

We’re born with a small stomach to demand food almost permanently and therefore, seek contact with our mother and guarantee our own survival.

The third day of life

Two important phenomena occur at this stage:

The combination of these two factors generates a great growth of the baby’s stomach. According to studies published to date, by the third day of life, the baby’s stomach doubles its capacity.

The tenth day of life

After the first week, breastfeeding is usually well established. Milk production continues to increase but at a more stable rate.

From the second week of life, babies begin to gain weight. This occurs after a period of physiological decline, during which excess fluid in the body is lost and breastfeeding takes hold.

Regarding the size of the stomach, the variations are more marked than before. They depend, to a great extent, on the child’s feeding rhythm, on the force with which they suckle the breast, on maternal production, among other factors.

According to representative models, on the tenth day of life, the baby’s stomach is about the size of a large chicken egg.

Parents hugging their newborn as he nurses.

The importance of knowing the anatomical and physiological changes in babies

Knowing how a child grows is important in order to support the feeding and breastfeeding guidelines. Just the same, these data are approximate, and as of today, the size of the baby’s stomach at birth isn’t exactly known.

It’s important to note that maintaining inappropriate breastfeeding practices from the very early stages of life can produce negative changes in the child’s body. They also increase the likelihood of certain long-term diseases, such as obesity.

For this reason, it’s important to talk with your doctor or lactation consultant to adopt good eating habits from day one.

All cited sources were thoroughly reviewed by our team to ensure their quality, reliability, currency, and validity. The bibliography of this article was considered reliable and of academic or scientific accuracy.

  • Folgoso C, Martinón Torres N, Martín Martinez B. Nutrición durante los primeros 1000 días de vida. EnRomán Riechman E et al. Tratamiento en Gastroenterología, Hepatología y Nutrición Pediátrica. Editorial Ergon. 5°edición. Madrid. 2021.
  • Watchmaker et al. Newborn feeding recommendations and practices increase the risk of development
    of overweight and obesity. BMC Pediatrics (2020) 20:104.
  • Spangler A, Randenberg A, Brenner M, Howett M. Belly Models as Teaching Tools: What Is Their Utility?
    J Hum Lact 2008 24: 199. DOI: 10.1177/0890334408316079. Disponible en:
  • Zangen S et al. Rapid Maturation of Gastric Relaxation in Newborn Infants. Pediatr Res 50: 629–632,
    2001. DOI 0031-3998/01/5005-0629. Disponible en:
  • Martin Calma J. Lactogenesis. En Comité de Lactancia Materna de la Asociación Española de Pediatría. Lactancia Materna: Guía para profesionales. Editorial Ergon. Madrid. 2004
  • Belly Balls Cards. Disponible en: Downloaded on May 2021.

This text is provided for informational purposes only and does not replace consultation with a professional. If in doubt, consult your specialist.