One of the first things that a new parent announces after the arrival of a baby is the baby's weight and length, or height. Babies can actually be surprisingly long since their legs are usually curled in and you can't see their full length. However, even a "tall" baby may not grow into a tall adult, and a "short" baby may go on to break height records. Understanding the averages for newborns and their growth patterns can help parents to monitor healthy development.
The Centers for Disease Control and Prevention publishes growth charts for babies, including the percentage of babies who share that height and weight. According to the CDC, about 50 percent of boys are about 19.75 inches at birth, while about 50 percent of girls are about 19.4 inches at birth. The CDC reports that girls are typically anywhere from 17.5 to 21.5 inches at birth, and boys are anywhere from 17.75 to 21.75 inches at birth.
Factors Influencing Length
A number of things may influence how long a baby is at birth. KidsHealth.org says that family genetics are a large contributing factor, including how big or tall each of a baby's parents are and how long they were at birth. A mother's health and nutrition during pregnancy can also influence the baby's development in utero, which can influence length at birth. KidsHealth.org also says that first babies tend to be smaller than babies born later to the same mother, and that twins and triplets tend to be born smaller.
No matter how long babies are at birth, most will grow rapidly during their first year of life. The Mayo Clinic says that babies grow about 1/2 inch to an inch per month during the first six months of life. From 6 to 12 months, most babies grow about 3/8 inch per month. A baby's length may not be as important as a baby's rate of growth. The key is that babies continue to grow in weight and length steadily over the first year.
When to Be Concerned
The best way to be sure that a baby is showing healthy development is to attend regular well-baby visits with a pediatrician. A baby's doctor can monitor growth over time to make sure that there are no underlying conditions that may be influencing factors like length or weight. Most pediatricians chart a baby's length and weight against the CDC growth chart, and most baby's stay close to the same percentile as they grow.