I'm Worried My Baby Isn't Growing (Failure to Thrive)
The short answer
Failure to thrive, now often called growth faltering, means a baby is not gaining weight or growing as expected. It is important to know that babies naturally shift percentiles in their first two years, and being on a lower percentile is not the same as failure to thrive. True growth faltering involves crossing two or more major percentile lines downward and usually requires medical evaluation to determine the cause.
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By Age
What to expect by age
0-3 months
Weight gain in the first three months is typically rapid, averaging about 5 to 7 ounces per week. After an initial weight loss of up to 7 to 10 percent of birth weight in the first few days, babies should regain their birth weight by 10 to 14 days. If your baby has not regained birth weight by two weeks or is gaining less than 4 ounces per week, your pediatrician will want to evaluate feeding. Common causes at this age include difficulty latching, low milk supply, tongue tie, or formula preparation errors.
3-6 months
Growth velocity naturally slows slightly at this age but should remain steady. Babies typically gain about 3 to 5 ounces per week. If your baby's weight has crossed two or more major percentile lines on the growth chart, your pediatrician may want to investigate. It is worth noting that breastfed and formula-fed babies have different growth patterns, and the WHO growth charts, which are based primarily on breastfed babies, are recommended for all infants under 2 years.
6-12 months
As babies become more active with crawling and exploring, weight gain naturally slows to about 2 to 3 ounces per week. The introduction of solids sometimes leads to a temporary plateau as babies adjust. If your baby is losing weight or consistently dropping percentiles despite adequate feeding opportunities, your pediatrician may check for underlying causes such as food allergies, celiac disease, or metabolic conditions. Most cases of growth faltering at this age are related to caloric intake rather than a medical condition.
12-24 months
Toddlers grow more slowly than infants, and their weight gain may only be 3 to 5 pounds over the entire second year of life. Picky eating is very common at this age and can make parents anxious about growth, but most picky toddlers grow fine. If your toddler has dropped significantly on their growth curve, your pediatrician will likely evaluate their diet, look for underlying conditions, and may refer you to a pediatric nutritionist. The goal is to identify whether the issue is insufficient intake, increased caloric needs, or poor absorption.
What Should You Do?
When to take action
- Your baby is on a lower percentile but has been growing steadily along their own curve since birth
- Your baby dropped from a higher percentile to a lower one in the first 6 months and then stabilized, which often reflects finding their genetic growth pattern
- Your baby's weight dipped slightly during an illness but bounced back within a week or two
- Both parents are small in stature, and your baby is tracking along a lower percentile consistently
- Your baby has crossed two or more major percentile lines downward on the growth chart
- Your baby seems hungry all the time but is not gaining weight despite frequent feeds
- Your baby is significantly lighter or shorter than expected for their age and you are concerned
- Your baby is losing weight, appears listless or excessively sleepy, and is difficult to wake for feeds
- Your baby has signs of dehydration such as no tears when crying, sunken fontanelle, very few wet diapers, or dry cracked lips
Sources
Related Resources
Trust your instincts. If something feels wrong, reach out to your pediatrician.
Worrying about your baby means you care. That is a good thing.
Related Feeding Concerns
Slow Weight Gain in Breastfed Baby
Weight gain patterns vary among babies, and breastfed babies often grow differently than formula-fed babies - they tend to gain more quickly in the first three months and then more slowly from three to twelve months. This is normal and is reflected in the WHO growth charts. However, if your baby is consistently gaining less than expected or has dropped significantly on their growth curve, it is important to work with your pediatrician and possibly a lactation consultant to identify the cause and ensure your baby is getting enough milk.
Baby Not Drinking Enough Milk
Babies naturally vary how much milk they drink from day to day, and a temporary dip in intake is usually nothing to worry about. Common causes include growth pattern changes, distractibility, teething, mild illness, or simply not being as hungry on a particular day. As long as your baby is having plenty of wet diapers and continuing to gain weight along their growth curve, they are likely getting enough.
My Baby Isn't Interested in Food
Many babies show limited interest in food when solids are first introduced, and this is usually perfectly normal. Babies develop at different rates, and some take weeks or even months to become enthusiastic eaters. As long as your baby is still getting adequate milk and growing well, a slow start with food is not a cause for concern.
Signs of Low Milk Supply
Many parents worry about low milk supply, but true low supply is uncommon. The most reliable signs your baby is getting enough milk are: adequate wet and dirty diapers (6+ wet diapers per day after day 5), steady weight gain, and your baby seeming satisfied after most feedings. Breast size, feeling "empty," baby wanting to nurse often, or pumping small amounts are NOT reliable indicators of low supply. If you are concerned, have your baby weighed and talk to a lactation consultant.
Toddler Picky Eating
Picky eating is one of the most common and normal behaviors in toddlers, peaking between ages 2 and 3. It is a developmentally appropriate way for toddlers to assert independence and learn about their world. Most picky eaters grow out of it and end up with a varied diet by school age, especially when parents continue to offer foods without pressure.
Baby Reflux / GERD
Gastroesophageal reflux is very common in babies because the valve at the top of the stomach is still maturing. Most infant reflux is uncomplicated, meaning your baby spits up but is otherwise happy and growing well. True GERD, where reflux causes pain, feeding difficulties, or poor weight gain, affects a smaller number of babies and is very treatable.