Slow growth caused by a medical problem

Is my baby’s slow growth caused by illness?

A medical problem can prevent a baby from growing well. Such babies may not be able to breastfeed or keep in enough milk. Some sick babies may not be able to grow properly even when given extra milk. Problems can develop soon after the baby’s birth or later on; some are obvious and some less so. Sometimes it is hard to tell whether a baby is just not getting enough milk or is sick as both can result in poor growth. A baby who is underfed because of breastfeeding problems will grow well when the problem is fixed and, if appropriate, milk supplements are started. A baby with a medical problem may not be able to breastfeed or keep in enough milk or grow properly because of the nature of their illness. They may not gain any faster if given milk supplements.

A) Describing slow growth caused by a medical problem

By one month of age, this baby was feeding for short periods, vomiting frequently, and not growing. Before-feed and after-feed weights showed that the baby was only taking in about 250 ml (8 oz) of breast milk each day. The mother could pump an additional 300 ml (10 oz) each day but the baby refused all supplements. The baby only started gaining after undergoing surgery for a twisted bowel at three months. He was temporarily supplemented with breast milk after surgery.

There are many possible reasons for a baby to not grow well. One reason is that the baby has a medical problem (Cole 2011). 

Medical problems can show up in many different ways. Some problems are very obvious, such as a cleft palate, and others are less obvious, such as a bladder infection or a heart defect.

Some problems, such as an abnormal bowel or a genetic disorder, may show up right after birth, while others, such as an infection, may develop later.

It is important to understand the difference between poor growth caused by not taking in enough milk and poor growth caused by a medical problem as the causes and treatment are different. Indeed, we have seen numerous babies misdiagnosed as having a breastfeeding problem, but who actually had a medical problem. 

Please consult your health-care providers if your baby is growing slowly or you believe your baby may be sick.

B) How medical problems cause slow growth

Medical problems can affect the baby's growth in three main ways:

1) A medical problem that interferes with breastfeeding

Some babies cannot breastfeed effectively because of a medical problem such as a cleft palate. Other causes include:

  • A blockage of the nasal passages (choanal atresia)
  • A blockage of the airway (laryngomalacia, paralysis of the vocal cords)
  • A very short jaw bone (retrognathia)
  • A fluid-filled sac (cyst) in the tongue

These babies generally show clear signs of being underfed unless supplemented with milk. They will gain quickly when they are supplemented. The supplementing tool will need to be appropriate for the baby’s problem.

2) A medical problem that prevents the baby from keeping in milk

Babies who cannot keep in enough milk usually have obvious signs such as vomiting or very large amounts of spitting. They may have a blockage or other abnormality of the throat, swallowing tube (esophagus), stomach, or bowels. These babies often need urgent attention and even surgery (Wiechers 2020).

They generally show clear signs of being underfed such as being thin or having poor weight gain but milk supplements do not usually improve their growth significantly.

3) A medical problem that prevents the baby from growing well

Babies who have a less obvious problem may gain very slowly but seem well otherwise.

a) Examples of medical problems that can result in poor growth

We have seen babies with the following problems being misdiagnosed as having breastfeeding problems:

b) Characteristics of babies with medical problems that result in poor growth

These babies are generally content, may not look particularly thin, and do not gain faster with milk supplements and may even refuse them. They gain slowly and are short.

These babies may:

  • Have lips that turn blue during breastfeeding.
  • Breathe hard while feeding. 
  • Not have much energy.
  • Have frequent infections.
  • Refuse milk supplements.

They may show abnormalities when examined by a health-care provider and require additional tests such as blood, X-ray, ultrasound, scoping, and genetic analysis to find out what is wrong.

C) Maintaining the milk supply

If the baby cannot breastfeed effectively and take in enough milk to grow well, mothers of such babies need to express after, or instead of breastfeeding. This provides milk for the baby’s supplements and maintains the milk supply until the baby is healthy enough to breastfeed effectively.

Breast milk is the ideal food for nearly all sick babies.

D) Deciding whether a baby is underfed or sick

Underfed babies who are well but have breastfeeding challenges and sick babies may both grow slowly. There are some ways to tell them apart.  

1) Signs of a medical problem

Underfed babies are often thin but will seem otherwise well. Sick babies may have other signs of illness and some are small but not thin. 

2) Response to supplementing

Babies who are underfed because of breastfeeding problems will grow quickly and normally when breastfeeding challenges are addressed and, if appropriate, they are supplemented with milk.

Sick babies who are unable to grow may not respond to these measures. They may be uninterested in taking in more milk and refuse both the breast and milk supplements.

3) Measuring breast milk amounts

Sometimes it is useful to see how much milk a mother makes and how much milk a baby takes in. 


Cole SZ, Lanham JS. Failure to thrive: an update. Am Fam Doctor. 2011 Apr 1;83(7):829-34

Wiechers C, Thjen T, Koos B, et al. Treatment of infants with craniofacial malformations. Arch Dis Child Fetal Neonatal Ed. 2020 May 14:fetalneonatal-2019-317890