The short child: What causes children to grow?

Do you worry about whether your child’s height is normal? Growth is a
remarkable process that transforms a microscopic embryo into a newborn
baby approximately 20 inches long, and eventually into an adult, usually
between 5 and 6 feet tall. Biomedical research has provided great
insights into human growth, although much remains to be learned. We know
that children grow larger because the cells throughout their body
enlarge and then divide to form two cells, then each of those cells
enlarges and divides again.

A child’s height is primarily determined by the length of his or her
bones, and thus children grow taller because their bones grow longer.
The bones grow longer because they contain growth plates — thin layers
of cartilage found near the ends of the bones. Cartilage is a firm,
resilient material found in your ears and nose, as well as lining the
ends of your bones at the joints. Children also have cartilage farther
inside the bones, forming the growth plates. Within the growth plates,
cells divide and enlarge, producing more cartilage, which is
subsequently converted into bone, and this process causes the bones to
elongate.

Grwoth is rapid early in life, then slows
Prior to birth, your child grew at an enormous rate — starting as a
microscopic fertilized egg and then growing about 20 inches and about 6
to 9 pounds in the nine months of pregnancy. If that growth rate were to
continue after birth, the child would reach adult size in two or three
years! However, the growth rate slows down with age. In the first year
after birth, an average child grows about 10 inches in length, and in
the second year, a child usually grows about 5 inches. By the time he or
she is seven years old, the average child is only growing about 2 inches
per year.

The adolescent growth spurt
This progressive decline in the growth rate is interrupted by the
adolescent growth spurt (also known as the pubertal growth spurt).
Sometime after puberty starts, the child’s growth speeds up for a couple
of years. Most girls start puberty sometime between 8 and 13 years of
age. The first visible signs are breast development and pubic hair. In
girls, the growth spurt occurs early in puberty. Growth starts to speed
up even as the first signs of puberty appear. In boys, puberty starts a
bit later, usually between age 9 and 14. The first visible signs of
puberty are pubic hair and growth of the testes (testicles) and penis.
Unlike girls, the adolescent growth spurt in boys does not start early
in puberty; it occurs a year or two later. In both boys and girls, the
growth rate can double during the adolescent growth spurt, increasing
from 2 inches per year to 3 or 4 inches per year.

The end of growth
The adolescent growth spurt does not last very long. After one to two
years of rapid growth, the growth rate starts to slow. By the time a
girl has her first menstrual period (typically two years after the start
of puberty), the growth rate has usually fallen to approximately 2
inches per year. At this time, the average girl has about 3 inches of
growth remaining, but some grow little more than another inch while
others grow more than 4. Boys’ growth also slows as puberty comes to
completion.

Growth does not stop abruptly. The growth rate decreases gradually,
dropping from about 3 or 4 inches per year at the peak of the spurt to
about 2 inches the next year, then 1 inch per year, then 1/2 inch. By
the time the average girl reaches her 15th birthday and the average boy
reaches his 17th, they have less than an inch of growth left.

Remember that all these numbers are just approximations, and, as we’ll
discuss in the next section, the age at which growth tapers off varies
widely among individual children. Eventually, however, growth in height
does stop completely. In fact, the growth plates disappear from the
young man or woman’s bones, a process called epiphyseal fusion.
Once the growth plates are gone, no further increase in height occurs.

The rate of maturation
Different children mature at different rates. Dr James Tanner, a pioneer
in the field of growth research, compared the rate of maturation to a
musical tempo. This tempo can affect the child’s growth rate, how old he
or she looks, when he or she loses baby teeth, and when the child starts
puberty.

Some children mature at a slow tempo. These kids often look young for
their age and are shorter than average. They go into puberty late and so
they have their growth spurt later than most of their peers. When this
occurs, the child with the slow pace of maturation feels particularly
short because his friends are all shooting up in height. In a year or
two, however, the slowly maturing child will begin his growth spurt. By
that time, his friends’ growth will be slowing down and so the child
will start to catch up to his peers. Usually, he will continue to grow
after his friends have stopped growing. Some boys with a slow tempo of
maturation will still be growing after graduating from high school.
Slowly maturing children can end up short, average, or tall as adults.

Other children mature at a rapid tempo. They are often tall in
childhood. They also tend to go into puberty early. The resulting early
growth spurt can make them feel very tall compared with their friends.
However, these rapidly maturing kids tend to stop growing sooner, at
which time their peers tend to catch up. As with slowly maturing kids,
the adult height can be tall, average, or even short.

What controls growth?
Why does one child grow more rapidly than another? Why does one child
end up taller than another? Three principal factors regulate a child’s
growth:

  • Genetics
  • Nutrition and general health
  • Hormones

When a child is not growing at a normal rate, one or more of these three
factors are probably responsible.

Key points to keep in mind
Children grow taller because of growth plates present within their
bones. Growth is very rapid in early life but decreases with age. This
decline is briefly interrupted by the adolescent growth spurt, after
which the growth rate again decreases. Growth finally stops in late
adolescence, and the growth plates disappear. The tempo of growth and
physical maturation varies among different children, with some maturing
rapidly and others slowly.

Check out a height predictor tool here!

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