The concern that your baby is not gaining weight as expected can be unsettling for parents. While a slower-than-average growth rate is not always serious, it warrants close attention from a healthcare provider. The medical term for significant, sustained poor weight gain is “failure to thrive,” but most instances are resolved with simple adjustments. Understanding the difference between normal variations in growth and genuine concern is the first step toward addressing the issue effectively.
Understanding Normal Growth Patterns
A healthy baby’s growth is monitored by pediatricians using standardized growth charts (WHO or CDC). These charts track weight, length, and head circumference, comparing the child’s measurements to those of thousands of other children. Measurements are recorded as percentiles, indicating the percentage of babies the child is heavier than.
Newborns typically lose up to 7 to 10% of their birth weight in the first few days of life. They should regain this initial weight loss by two to three weeks old. Healthy infants usually double their birth weight by four to six months of age and triple it by their first birthday.
The consistency of the growth curve over time is more important than the percentile itself. A baby maintaining a steady curve along a lower percentile is likely healthy and simply small. Concern arises when a baby’s weight dramatically drops across two or more major percentile curves or when the rate of gain falls below expected standards. Infants generally gain about an ounce (30 grams) per day during the first three months.
Primary Causes Related to Feeding and Intake
The most common reason for poor weight gain is insufficient caloric intake, meaning they are not consuming or retaining enough food. For breastfed babies, this often stems from a poor or shallow latch, preventing efficient milk transfer. Inefficient feeding can also be caused by a tongue or lip tie, which physically restricts the baby’s ability to coordinate sucking and swallowing.
Low milk supply is another factor, sometimes due to hormonal issues or inadequate feeding frequency. Babies who fall asleep quickly at the breast or bottle often do not consume the necessary volume of higher-calorie hindmilk or formula. Solutions involve optimizing feeding technique, maximizing milk transfer, or increasing feeding frequency.
For formula-fed babies, preparation errors, such as diluting the formula with too much water, reduce the caloric density of the feed. Frequent, large-volume spitting up or vomiting, often due to reflux, also leads to poor weight gain because the baby does not retain the calories consumed. Distracted feeding sessions or overly rigid schedules that ignore the baby’s cues can also limit daily intake.
Identifying Less Common Medical Contributors
If a baby consumes adequate calories, poor weight gain may indicate an underlying medical condition affecting absorption or energy expenditure. Malabsorption prevents the body from extracting necessary nutrients, even with normal intake. Examples include severe food allergies, such as a cow’s milk protein allergy, which causes gut inflammation and nutrient loss through chronic diarrhea or vomiting.
Other gastrointestinal issues, like severe Gastroesophageal Reflux Disease (GERD) or conditions affecting digestive enzymes, interfere with nutrient processing. Chronic infections, such as urinary tract infections (UTIs), also divert energy away from growth. The baby’s immune system uses the energy that would otherwise be dedicated to growth to fight the infection.
A baby may also have a condition requiring them to burn significantly more calories than a typical infant. This is often seen with cardiac or pulmonary issues, where breathing or maintaining circulation demands a higher metabolic rate. Metabolic disorders, though less common, interfere with the body’s ability to convert nutrients into usable energy, resulting in poor growth.
Actionable Steps and When to Contact a Pediatrician
If concerned about weight gain, keep a detailed feeding and elimination log. Track the time and duration of every feeding, the volume of formula or side offered, and the number of wet and dirty diapers per 24 hours. A baby absorbing nutrients should have six or more wet diapers daily and regular, soft stools.
A pediatrician should be contacted promptly if a newborn has not regained birth weight by three weeks of age, or if an older infant falls significantly across percentiles. Urgent physical signs, or “red flags,” require immediate medical attention. These include signs of dehydration, such as a sunken soft spot (fontanelle), a lack of tears when crying, or significantly decreased urination.
Other urgent signs include persistent lethargy, extreme irritability, a weak cry, or sudden, unexplained weight loss after the newborn period. If the baby is experiencing persistent vomiting or diarrhea, or appears listless and unresponsive, seek emergency medical care. In less urgent cases, a pediatrician can observe a feeding session, recommend a lactation consultant, or initiate nutritional therapy for “catch-up” growth.