Baby is not gaining weight, low percentile, poor growth

Why Your Baby Is Not Gaining Weight

Why Your Baby Is Not Gaining Weight

Your baby has not gained as much weight as expected and you’re understandably worried. The first step is to determine if there is an underlying problem or whether it's a false alarm or due to unrealistic expectations.

Genuine problem or not? 

When a baby is not gaining as much weight as expected, it’s understandable that parents worry. In some cases, baby is growing well, but a false alarm gives the impression of poor growth. In other cases, there is genuine reason for concern. If this is the case for your baby, then identifying the underlying cause is obviously going to be helpful if you are to turn the situation around. 

The first step is to be sure there is reason for concern by observing for physical signs that may indicate poor growth.

Signs of poor growth

Poor growth occurs when a baby does not receive or retain enough calories/kilojoules to maintain growth in harmony with his genetic growth potential. Signs can include: 

  • Failure to gain enough weight or weight loss. Poor growth can occur suddenly or gradually over a period of months. A baby or child who gains insufficient weight may be classified as 'failure to thrive'.
  • Weight is well below length on infant growth charts.
  • Less than 5 wet diapers per day. This may indicate that baby is not receiving sufficient fluids.
  • Infrequent bowel motions.
  • Irritability and sleep disturbance owing to hunger.
  • Lethargy and excessive sleep can occur when a baby is weak or severely malnourished. 

Together these signs may point to an inadequate intake of milk and/or solid foods to maintain healthy growth. Separately, each of these signs can be due to other reasons. If the signs don’t add up in your baby's case, see Growth False Alarms.

Causes of poor growth

There are numerous reasons why a baby might grow poorly. These fall into 2 broad categories.

  1. Organic - due to an underlying physical problem, illness or medical condition.
  2. Non-organic - due to behavioral or social reasons.

Behavioral and social reasons account for more than 80 percent of children classified as ‘failure to thrive’. An underlying physical/medical cause, or combination of both physical/medical and behavioral causes, accounts for the remaining 20 percent.

Behavioral & social reasons babies of not gaining weight

Behavioral and social reasons for poor growth are generally due to the baby not consuming sufficient calories/kilojoules. But there are different ways in which this might occur, for example: 

  • Baby is not offered enough calories/kilojoules.
  • Baby is unable to take advantage of the calories/kilojoules offered. 
  • Baby refuses to consume adequate amounts.  

The reasons for these problems can differ according to feeding method. 

Breastfed baby

Baby is not offered enough milk.

Potential reasons include: low milk supply; rigid feeding schedules; or neglect. 

Baby is not able to drink enough milk.

A nursing mother could have an abundance of breastmilk and yet her baby may be prevented from accessing it.  Reasons include: poor latch; poor positioning; or sleep deprivation.

Baby is not willing to drink enough milk.

This means the mother has a plentiful supply of breastmilk, and her baby is physically capable of accessing this, but he/she refuses to feed or takes insufficient amounts to maintain healthy growth. Reasons include: breast refusal (also called nursing strike); starting solids too soon (before the age of 4 months); solids given before breastfeeds; or stress.

Bottle-fed baby

Baby is not offered enough milk.

Potential reasons include: errors in formula preparation resulting in watered-down formula; rigid feeding schedules; poverty; or neglect. 

Baby is not able to drink enough milk.

The baby is offered sufficient quantities of milk but is prevented from consuming enough. Reasons include: inappropriate or faulty feeding equipment; poor positioning of baby; errors in feeding technique; nipple ring is screwed down too tight; or too loose. 

Baby is not willing to drink enough milk.

The baby is offered enough milk and is capable of drinking from a bottle, but either refuses or takes only a little. Reasons include: starting solids too soon (before the age of 4 months); solids given before milk feeds; feeding aversion owing to being repeatedly force-fed; or stress. 

NOTE:  Babies under the age of 12 months require breastmilk or infant formula. Substituting other types of milk (eg regular cows’ milk or other types of milk) in place of breastmilk or formula can cause nutritional deficiencies and poor growth.


Baby is not offered enough solids.

Not offering a baby over the age of 7 months solid foods; or restricting solid foods.

Baby is offered too much solids at the expense of milk feeds.

The baby might fill up on solid foods (some are low in calories, essential vitamins and minerals) and then not want to drink sufficient quantities of milk. Reasons include: starting solids before the age of 4 months; solids given at the wrong time in relation to milk feeds; or adding cereal to bottles.

Baby is offered unsuitable food choices or too much of one type of food.

Reasons include: malabsoption problems owing to unsuitable food choices or too much juice.

Baby is unwilling to eat foods offered.

Baby might have decreased appetite due to night feeds extending beyond the age of 7 months; or too many milk feeds. Or he may be unable or unwilling to take solid foods due to sleep deprivation; or feeding aversion owing to being cajoled, harassed by repeated offerings when baby refuses; pressured or forced to eat solid foods. 

Bear in mind that there is often more than one behavioural reason for a baby to fail to gain sufficient weight, and these reasons can differ for each baby. Once you have ruled out all potential behavioral reasons for your baby’s poor growth, it's time to examine possible physical and medical reasons.

Physical & medical reasons for poor growth

In most cases of organic cause the reason will be identified within days of birth, but there are other physical problems that affect growth, which might not become evident until weeks or months down the track. 

To narrow the search for the cause of your baby’s growth delay it may help to consider the ways in which a baby might not receive sufficient energy (calories/kilojoules) for healthy growth.

  • Baby is not able to drink or eat enough.
  • Baby is not willing to drink or eat enough.
  • Baby cannot keep down and/or digest the milk or food consumed.
  • Baby has high energy requirements.
  • Growth hormone deficiency.

For each group there can be multiple different causes.

Baby is not able to drink or eat enough.

Reasons include: prematurity, a weak or uncoordinated suck, cerebral palsy, neurological problem such as hypotonia (low tone), cranial nerve palsy or neuromuscular weakness, tongue-tie, lip tie, cleft palate, retrognathia (receding chin), or macroglossia (large tongue). These problems will generally affect feeding from the time of birth.

Baby is not willing to eating or drinking enough.

This means baby is capable of feeding but is unwilling due to decreased appetite or due to a feeding aversion. Reasons for decreased appetite include: infection (eg respiratory, gastrointestinal or urinary infection), chronic illness, anemia, severe constipation, conditions that affect the brain, liver, or kidneys or pancreas may affect appetite. Sedative medications, some of which are prescribed to treat colic can make the baby too sleepy to feed effectively. (See anti-colic medications). Most of these problems are readily identifiable during medical examination or tests. A baby may be unwilling to feed if he has developed a feeding aversion due to the pain associated with acid reflux or milk or food allergy or intolerance.

Baby can’t keep down or digest and/or absorb the food he ingests.

This implies baby is drinking or eating enough milk or food but something is preventing his body from taking full advantage of this. Baby may lose calories/kilojoules consumed due to vomiting and/or diarrhea. Possible reasons include, obstructions like pyloric stenosis or esophageal atresia, gastrointestinal infection, severe reflux, malabsorption problems due to cows’ or soy milk protein allergy, and a number of congenital and genetic conditions, disorders or abnormalities.

Baby has high energy (calories/kilojoules) requirements.

Growth failure can be due to an acute or chronic condition that increases baby’s energy requirements.  For example, cardiac conditions, chronic lung, kidney can place a greater demand on a child’s energy (calories/kilojoules) requirements.

Growth hormone deficiency.

Poor growth will occur from birth.

This list is not inclusive of all physical problems that can cause poor growth. 

Before panicking that your child might have a physical problem affecting his/her growth that the doctors have been unable to detect, see 'Growth False Alarms' and if still concerned have your baby examined by a doctor.  If your baby is currently being treated for a physical and medical condition without improvement in growth, consider the possibility of a coexisting behavioral cause.

Written by Rowena Bennett

© Copyright 2020. All rights reserved. Permission from author must be obtained to copy or reproduce any part of this article. 

‘Your Baby's Bottle-Feeding Aversion’ book

In my book, ‘Your baby’s Bottle-feeding Aversion’, I have described physical and behavioral reasons for babies to develop an aversion to bottle-feeding. How to identify the cause and the solutions to match. Included are step-by-step instructions on how to regain your baby’s trust and resolve a feeding aversion caused or reinforced by repeated pressure to feed.

While the book was written for bottle-fed babies, many nursing mothers have found that applying the same strategies has also helped them to successfully resolve a breastfeeding aversion.

You might find that reading this book is all you need to do to understand the steps you need to take to resolve your baby’s feeding aversion and get him back to the point of enjoying eating until satisfied. 

Baby Care Advice Consultations

If you would like an individualized assessment of all reasons for infant feeding problems, not just feeding aversion, we also provide a consultation service. Baby Care Advice consultants have extensive experience in pinpointing the cause of feeding aversion and other behavioral feeding problems such as those related to equipment and the parent’s feeding practices. (For more on what’s included in a consultation).