Baby Not Growing Fast Enough - Failure to Thrive
The short answer
Slow weight gain (falling across percentile lines on the growth chart) can have many causes, ranging from simple (not getting enough calories, growth pattern recalibration) to medical (feeding difficulties, food allergies, malabsorption, or underlying conditions). "Failure to thrive" is a clinical term for weight that falls below the 2nd percentile or drops across two major percentile lines. The most common cause is insufficient caloric intake - the baby is not eating enough, not absorbing enough, or burning too many calories. Early evaluation is important because nutrition affects brain development.
By Age
What to expect by age
Newborns lose up to 7-10% of birth weight in the first week and should regain it by 2 weeks. After that, expect about 1 oz per day (6-7 oz per week) of weight gain. If your newborn has not regained birth weight by 2 weeks, feeding should be evaluated. Breastfed babies with slow gain may need: more frequent feeds, better latch assessment, supplementation while increasing supply, or evaluation for tongue tie. Formula-fed babies with slow gain may need: more frequent feeds, concentrated formula, or evaluation for feeding difficulties.
Weight gain typically slows to about 4-5 oz per week. A drop of one percentile line can be normal (genetic recalibration - large newborns of small parents may settle into lower percentile). But dropping across two percentile lines is a concern. If your baby is feeding well but not gaining, your pediatrician may check for: cow's milk protein allergy (especially if there is blood in stool or eczema), reflux causing food refusal, or malabsorption. Frequent weight checks (every 1-2 weeks) help track the pattern.
Weight gain continues to slow naturally to about 3-4 oz per week. Active babies who are crawling and pulling up may have periods of slower gain because they are burning more calories. If your baby is small but following their own curve, eating solids with interest, and meeting milestones, they are likely fine. If weight continues to drop off their curve, your pediatrician may suggest: calorie-dense foods (avocado, nut butters, olive oil), fortified formula, or evaluation for underlying conditions.
Toddlers are notoriously picky and may eat very little some days. Weight gain slows to about 3-5 pounds per year. If your toddler is active, meeting milestones, and following their own growth curve (even if it is a low percentile), they are likely growing appropriately. Concern arises if: weight drops off their established curve, they are crossing percentile lines downward, they have very limited dietary intake, or they seem lethargic and unwell alongside poor growth.
What Should You Do?
When to take action
- Your baby dropped from a high birth percentile to a lower one by 6 months and then tracked steadily - this is genetic recalibration
- Your baby is small (low percentile) but has always tracked along the same curve and is meeting milestones
- Your breastfed baby is gaining slower than formula-fed peers but is still following their curve
- Your toddler's weight plateaued briefly during an active developmental period like learning to walk
- Your baby has dropped across one major percentile line on the growth chart
- Your baby is gaining less than expected despite adequate feeding
- Your baby is small and also seems excessively tired or not meeting developmental milestones
- You are struggling to get your baby to eat enough and need feeding support
- Your baby has dropped across two or more percentile lines or fallen below the 2nd percentile
- Your newborn has not regained birth weight by 3 weeks
- Your baby is lethargic, not feeding, and appears dehydrated alongside poor growth
- Your baby is losing weight (not just gaining slowly)
Sources
Related Resources
Related Physical Concerns
Baby Growing Too Fast - Rapid Weight or Height Gain
Babies come in all sizes, and being on a high growth percentile does not automatically mean something is wrong. What matters more than the percentile itself is the pattern - a baby who has always tracked along the 90th percentile is following their own normal curve. Rapid upward crossing of percentile lines (jumping from the 50th to the 95th) is more noteworthy. Breastfed babies cannot be overfed at the breast. For formula-fed babies, ensure appropriate bottle feeding practices. Most "big babies" simply have big parents and are growing as genetically programmed.
Baby Not Growing Taller - Short Stature Concerns
Height (length) is primarily determined by genetics - if parents are shorter, their child will likely be shorter. A baby who is consistently at a low height percentile but follows their own curve is most likely genetically small. Concern arises when a child's length drops across percentile lines or when length is significantly lower than what would be expected based on parental heights. Growth hormone deficiency, thyroid issues, and certain genetic conditions can affect height, but these are uncommon. Most short children are simply constitutionally short or have constitutional growth delay (late bloomers).
Signs of Nutritional Deficiency in Toddlers
The most common nutritional deficiencies in toddlers are iron, vitamin D, zinc, and calcium - especially in picky eaters and children who drink excessive amounts of milk. Signs of iron deficiency (the most common) include pallor, fatigue, irritability, poor appetite, and slow weight gain. Most picky toddlers get adequate nutrition despite their limited diets, but if your child eats fewer than 10-15 foods total or avoids entire food groups, a nutritional evaluation may be helpful.
My Baby Seems to Use One Side More Than the Other
Babies should use both sides of their body fairly equally during the first 18 months of life. While slight preferences can be normal, a consistent pattern of favoring one side - using one arm much more than the other, crawling with one leg dragging, or turning the head predominantly one way - should always be discussed with your pediatrician. Early identification of asymmetry leads to the best outcomes.
Baby or Toddler Body Odor - When Is It Normal?
Babies and toddlers can develop body odor from several benign causes: sour milk caught in skin folds, sweating, diaper area odor, strong-smelling foods in the diet, and certain medications or vitamins. True body odor (like adult BO from apocrine glands) should not occur before puberty. If your baby or young toddler has a persistent unusual body odor that is not explained by skin folds, diaper, or diet, it could indicate a metabolic condition, infection, or foreign body (especially in the nose or vaginal area). Unusual persistent odor warrants a doctor visit.
Baby Born with Teeth - Natal Teeth
Natal teeth (teeth present at birth) occur in about 1 in 2,000-3,000 births. In most cases, these are actual primary (baby) teeth that erupted early, not extra teeth. Most natal teeth are the lower front incisors. While natal teeth can sometimes cause breastfeeding difficulties or have a risk of becoming loose and being a choking hazard, many can be left in place and monitored. The decision to keep or remove a natal tooth depends on how firmly it is attached and whether it is causing problems.