Average baby weight at birth

The average weight for full term infants is 7.6 lbs (121.6 ounces).  As soon as your baby is born, their weight will be checked. While all newborns are born at different weights, the average weight range is between 5 pounds and 8 ounces to 8 pounds and 13 ounces. Babies born outside of this range aren't necessarily unhealthy or experiencing abnormal growth, but they may require extra medical attention.

According to Summer Health pediatricians, a baby's weight gain is an important developmental milestone to track. A newborn’s weight depends on factors including the baby's health, the length of the pregnancy, the mother's health and nutrition during pregnancy, and when the baby was born. Additional factors that can influence your baby's weight are:

• Genetics and parent size 

• Underlying genetic or metabolic conditions 

• Whether it's a single or multiple birth 

• Gender 

Average baby weight gain by month

During their first year, babies experience rapid growth and have important weight developmental milestones every month. Newborn babies typically gain around 30 grams (1 ounce per day until they reach three months. From three to six months, a baby will gain about 20 grams (0.67 ounces) daily, and from six to twelve months, their growth slows to approximately 10 grams (0.35 ounces) per day. 

Average length at birth

A full-term baby is typically around 20 inches (50 cm) long at birth. In the first six months, babies grow about an inch per month. Between seven and twelve months, a baby's growth slows to roughly half an inch per month.

Factors that affect newborn length

• Genetics/size of parents

• Prenatal and maternal nutrition

• Maternal health during pregnancy

• Maternal iron levels

• Maternal rest during pregnancy

• History of smoking 

• Underlying genetic or metabolic conditions

What are growth charts?

During well-check visits, your pediatrician will likely provide information about your baby's growth based on an infant growth chart, an important developmental milestone. This chart tracks your baby's head circumference, weight and length, and pattern of growth at different ages.

At each well-visit, your pediatrician will track your baby's measurements and input them into a growth chart to compare their growth patterns with other babies. If your child falls into a higher percentile, they are larger than average. If they fall into a lower percentile, they are smaller than average. For example, if your child is in the 20th percentile for weight, it means they weigh more than 20% of kids their age and less than 80%.

Pediatricians use two charts: one by the World Health Organization (WHO) for babies under age 2 and another by the Center for Disease Control (CDC) for children aged 2 and up. The CDC growth chart specifically reflects the growth patterns of American children using data collected since 1977. More recently, the WHO growth chart includes additional factors that may affect growth like racial and ethnic background, body mass index (BMI), premature birth, and accounts for differences in breastfed and formula-fed babies.

As babies grow and develop, they typically follow a consistent growth curve. For example, a child in the 5th percentile will likely continue growing along the 5th percentile over time. Weight changes only become a concern if a child or baby experiences a sudden and significant drop or gain across multiple percentiles.

Newborn weight loss

It's normal for newborns to lose weight in the first few days after birth. In fact, healthy babies typically lose 7% to 10% of their birth weight during that time. After a few days, babies usually begin to regain this weight and return to their birth weight within the first two weeks after birth.

Common causes of poor gain weight in a baby 

• Feeding difficulties or poor latch

• Food sensitivities 

• Milk protein intolerance

• Transient illness or infection

• Gastrointestinal issues like gastroesophageal reflux or celiac disease

• Swallowing problems, seen in children with cleft lip/palate or cerebral palsy

Newborn growth spurts

Newborns have growth spurts throughout their first year, usually between 2 to 3 weeks postpartum, and then at 6 weeks, 3 months, and 6 months.

When to call your pediatrician

If your child is experiencing poor feeding, has few wet diapers, seems lethargic, isn't gaining weight, or is losing a significant amount of weight, consult your local or Summer Health pediatrician for additional guidance.