Apart from the nine months of growth before birth, children grow most rapidly during the first year of life. At birth, girls and boys are usually 46 to 54 centimetres (18 to 21 inches) in length. Most full-term girls weigh 2.6 to 4.1 kilograms (5.7 to 9.0 pounds), and boys 2.4 to 4.4 kilograms (5.3 to 9.7 pounds).
Healthy babies may lose up to 10 per cent of their birth weight in the first few days of life, but usually regain it after 10 to 14 days. They double their birth weight by five months and triple it by the first birthday.
The average rate of growth throughout childhood and adolescence is shown in Figure 1 above. The period of most rapid growth is during the first two years, then gradually slows until the start of the adolescent growth spurt. From age three until the beginning of puberty, most children grow at least five centimetres (two inches) a year. At puberty girls have an earlier and slightly smaller growth spurt than boys.
Puberty in girls is usually marked by the appearance of small breasts at age 10, but this can range from age seven to 13 years. Early pubic hair appears about six months later. Typically, menstruation begins a month or two before age 13, but the range is from 10 to 15 years. Early menstrual cycles are often quite irregular and unpredictable.
The first sign of puberty in boys is gradual enlargement of the testicles around age 12, although this can appear from nine to 14 years. Genital enlargement and appearance of pubic hair follow. Normally, girls reach adult height at 16 years, two to three years after menstruation starts. Boys normally reach adult height at age 18.
Many things decide how a child will grow. Events that occur before birth may be important. Other factors include heredity (growth patterns of other family members), nutrition, and various childhood illnesses. Several chemicals (hormones) in the body play an important role in growth.
Events before birth: The health of the mother during pregnancy has an important effect on the size of her baby at birth. Infants born to mothers who smoke heavily or consume alcohol during pregnancy are often small at birth. They may also grow poorly after delivery. Mothers who are ill or poorly nourished during pregnancy may have babies with a low birth weight.
Most premature babies grow rapidly after delivery and are of normal size by the age of two. This is also true of babies whose development was disrupted in the last three months of the pregnancy. On the other hand, serious illness during the first three months of pregnancy may result in a baby who is not only small at birth, but remains small throughout life.
Heredity: The height of the parents is important to consider when assessing a child’s growth. During the first three years of childhood, babies whose parents are tall may grow faster than babies of short parents. If accurate measurements of the genetic parents’ heights as young adults are available, we can estimate the child’s ‘target’ height as an adult.
For girls, take the average of the parents’ height in inches (height of the mother plus the height of the father divided by two) and subtract 2.5 inches. For boys, take the average of the parents’ height in inches and add 2.5 inches. For instance, the target height for a girl with a 5’7” mother and 5’11” father would be 5’6.5”. The target height for a boy with the same parents would be 5’11.5”.
Nutrition: A healthy diet appropriate to the age of the child is essential for normal growth. Include enough calories for energy, with proper amounts of carbohydrate, fat, protein, vitamins and minerals. A child who eats a well-balanced diet does not need vitamin, mineral or other supplements. Indeed, some may suffer harmful effects if these are used unwisely. If in doubt, ask your doctor or a registered dietitian for advice.
General health: During acute (short-term) illness, a child may lose or fail to gain weight. This is temporary and will not cause permanent growth problems. However, chronic (long-lasting) illness may interfere with a child’s growth. If not corrected, there may be permanent loss of some growth potential.
Hormones: Hormones are chemical messengers produced by endocrine glands in the body and released into the bloodstream. They affect the function of cells throughout the body. The thyroid hormone, thyroxin, helps control the metabolism of various body tissues. Too little thyroxin (hypothyroidism) results in poor growth and excess weight gain. Too much (hyperthyroidism) can mean unexplained weight loss, even in children who are eating well.
The liver and other tissues change the growth hormone produced by the pituitary gland into a hormone called insulin-like growth factor 1 (IGF-1). This hormone affects bone growth throughout the body. Too little growth hormone or IGF-1 is an uncommon but important cause of failure to grow during childhood.
Adrenal glands sit on top of each kidney. Cortisol released from these glands has metabolic effects throughout the body. Too much may result in poor growth and excess weight gain. This is often seen in children who receive high-dose corticosteroids for a variety of medical conditions. These include severe – asthma, leukemia, arthritis, and inflammatory bowel disease.
At puberty, sex hormones have a strong affect on growth and maturation. In girls, estrogen is released by the ovaries. In boys, testosterone is released by the testicles. Both hormones stimulate growth and are partly responsible for the adolescent growth spurt.
If puberty is delayed, a child may grow more slowly than others of the same age. On the other hand, early puberty in a very young child can cause more rapid growth than expected. Even if they are very tall as children, boys and girls who experience puberty too early may be short as adults since the growth plates at the end of the long bones close too quickly. Once growth plates close, it is not possible to grow taller.
Help make certain that your child is growing normally by scheduling regular visits with your family doctor or pediatrician (children’s doctor) on a regular basis. Healthy children should be seen every three months during the first year of life, every six months during the second year, then once a year afterward. The doctor should plot the child’s height and weight on a growth chart like the ones shown in Figure 2.
A child on the fiftieth percentile is of average size, meaning 50 per cent of children of the same age and sex are smaller and 50 per cent are taller. Normal, healthy children will usually be between the third and ninety-seventh percentiles. After three years of age, a child’s height and weight should follow the same percentile curve.
If a child’s height or weight is below the third or above the ninety-seventh percentile, or if height or weight is not following the percentile curves, see a doctor. Although most of these children are healthy, the doctor may find a problem that needs further testing or treatment.
When growth problems are discovered, the doctor will take a careful medical history of the child and the family. Details on diet, current and previous illnesses, medications, injuries and stays in hospital are important. The heights, weights and growth patterns of parents, and brothers and sisters are also relevant. Sometimes, even details about aunts, uncles and grandparents are considered.
The child’s height and weight are measured, and a general physical examination is done to look for problems. Lab tests, including blood and urine tests, may be recommended to rule out various medical conditions. A special x-ray of the hand and wrist, called a bone age, can help to assess the maturity of the bones and skeleton. This x-ray is particularly helpful in estimating a child’s growth potential. Short children whose bone age is significantly younger than their actual age may be able to catch up in terms of growth.
Occasionally, a doctor may refer the child to a specialist for further assessment. In certain cases, a test of growth hormone secretion may be recommended. These tests are not done on all short children. They are used if growth seems abnormal and other causes have been ruled out.
Growth hormone levels normally vary widely throughout the day. Aerobic exercise, deep sleep and several medications can stimulate secretion by the pituitary gland. Blood samples are normally taken every 20 to 30 minutes for two to three hours to determine whether the hormone is being released normally. If a child cannot produce growth hormone normally, a synthetic form of the hormone may be given. This may help restore normal growth. Additional tests, CT or MRI scans may be done to find out why a child is not making growth hormone normally.
In Canada, growth hormone is approved for use only by children who have growth hormone deficiency, chronic kidney disease before a kidney transplant, or Turner Syndrome. Very recently it has been approved for use by low birth weight babies. These are not babies who are premature. Rather, they are born small for their age based on the number of weeks from the beginning of the pregnancy.
When growth problems are present, specific treatment can help correct the cause. Even if children have normal variations of childhood growth patterns, it is essential to provide lots of emotional support. Children who are taller or shorter than their peers are often teased. Parents, teachers and others need to have expectations of children based on their age and stage of development, not on their physical size.
Children who are shorter or taller than others should be encouraged to participate in sports and other activities that they can enjoy regardless of size. Small children may do well in swimming, gymnastics, diving, martial arts, skiing, snow boarding, mountain biking, long distance running, dancing, horseback riding, art or music. Tall children may prefer basketball, volleyball, football, or hockey.
Try to keep your relationship with your child open so that emotional problems or concerns can be recognized early and discussed freely. Help is available if professional counselling is needed. Finally, if you have questions about the growth of your child, talk to your family doctor, pediatrician or public health nurse. They are excellent resources and very willing to help.