Height age is a term used to refer to the specific parameters of a child’s height. The height age can be used in a variety of ways to determine the child’s growth or height and other parameters of his health.
Several studies have been conducted to assess the impact of height age and the ways to apply it. Here is a detailed description of what the height age means and how it helps to evaluate the child’s growth.
What is height age?
Height age refers to the age that corresponds to the height of the child when marked on a growth chart on the 50th percentile. It can help to evaluate the short and tall stature in children.
Let us have a look at the application of height age for assessing the growth of a child.
Evaluation of tall and short stature in children based on the height age
Children whose growth velocities and heights deviate from the normal range or percentiles on the standard growth charts represent a special challenge to parents and physicians.
If the height of the child is more than the 97th or less than the 3rd percentile, he or she is deemed taller or shorter in stature, respectively.
The growth velocity, which is outside the normal range of about the 25th-75th percentile could also be considered abnormal.
Measurements of the height of a child over a period of time documented on the growth chart can serve as a key, in such cases, for identifying abnormal growth.
Tall and short statures are usually caused due to the variation in the normal growth pattern, though some patients might have serious pathologies underlying the abnormal rate of growth.
A comprehensive medical history of the child and physical examination often helps to differentiate the abnormal growth pattern from normal variants. It can also help to identify dysmorphic features cause due to genetic syndromes.
The patient’s medical history and the findings of physical examination can also guide laboratory testing.
This indicates that parents and primary physicians should make efforts to evaluate the growth of the child and determine whether it is in the normal range of percentile. In case the height or growth velocity is found to be lower or higher than normal, a comprehensive medical history and physical examination must be conducted to identify the possible causes.
Further laboratory testing may be recommended to confirm the diagnosis.
The height age of the child determined based on these factors could play a critical role in finding whether the growth velocity and the height of the child are normal.
Also, regular visits to the primary care physician can help in identifying children with an abnormal rate of growth.
If the shorter or taller stature is believed to be the result of the variant in the normal growth pattern, the strategy of ‘wait & watch’ with regular assessment and observation of the related health parameters is recommended.
This can allow the doctors to detect any abnormality at the earliest and provide appropriate treatment to prevent further complications.
However, if the examination reveals that the child suffers from dysmorphic features, he should be referred to an endocrinologist and a geneticist for further evaluation and treatment.
A comprehensive history and physical examination should be performed in all children with abnormal growth, and appropriate laboratory studies should be recommended based on these findings. 
Here are some ways physicians can adopt to assess the bone age and height age of the child.
How to measure the bone age and height age of children?
- The use of a growth chart is considered critical for monitoring the child’s growth as well as overall health. During each visit, the accurate weight and height measurements of the child should be plotted on the longitudinal growth chart. 
- Ideally, the accurate weight and height of the child should be measured frequently for more than 6 months for a better assessment of his growth trend. Series of measurements of heights and weight over a longer period can provide a better idea of the height age of the child than the shorter period of measurement or very few numbers of measurements.
- Mid-parental height can also be used to calculate and determine the relationship between the child’s present height and the parents’ heights.
- If the projected height of the child differs from his genetic potential by more than 2 inches or 5 cm, he should be referred to an endocrinologist for further evaluation.
- Bone age radiography of the child can be obtained for determining the relationship between his skeletal age and the chronologic age. If the child’s bone age is delayed or advanced by more than 2 standard deviations, he should be referred to an endocrinologist.
These are some recommendations to apply the height age of the child to detect the abnormalities linked to his growth or future height.
Being aware of the importance of height age can also allow parents and doctors to detect any genetic abnormality that may lead to a very short or very tall height.
It is advisable to compare the growth chart of the child to the standard measurements for different ages. Assessment of the growth pattern of the child based on the normal growth pattern can provide vital clues about the presence of any abnormality and its causes.
Here is a brief discussion about what a normal growth pattern is and how it helps to determine the child’s height age or bone age.
Normal Growth Pattern
The height of a newborn is usually determined by the intra-uterine environment that is influenced by factors like maternal size and the general health, nutrition, and social habits of the mother.
For example; children of mothers who were exposed to active or passive smoking during or for a few months before the pregnancy are more likely to develop genetic abnormalities that could affect their height.
The average weight of children at birth is around 3.25 kg (7 lb, 3 oz), and the average height is 19.7 in (50 cm).
The growth rate after birth is more dependent on the genetic background of the infant.
An important phenomenon, called the catch-down or catch-up growth, tends to occur in infants within the first 18 months after birth. In about two-third of infants in this age group, the growth rate percentile continues to shift linearly until the child has reached his genetically determined height percentile or growth channel.
Some children may catch-up on the growth chart faster because their parents are tall while those who have shorter parents may move down on the chart.
By the age of 18 to 24 months, the height of most children seems to have shifted to their genetically determined height percentiles.
Thereafter, the growth proceeds typically along the same percentile until puberty.
However, in children with conditions that can affect their growth and development such as growth hormone deficiency, the normal birth height and weight might be followed by a sustained deceleration in the growth starting at 3 to 9 months of age.
Also, beyond 2 years of age, the child may exhibit a constitutional delay in growth, as well as puberty, at a rate that is parallel to around the 3rd percentile. Children who suffer from conditions like growth hormone deficiency, renal acidosis, and Crohn’s disease may also have a growth pattern that falls progressively below the 3rd percentile.
So, if the child’s height age falls below or above the normal range of percentile, it should be considered a sign of an underlying disorder. Physicians should make efforts to detect the cause so that the appropriate treatment can be initiated at the earliest to minimize the impact of the condition on the child’s growth, future height, and overall health.
This is how the comparison between the child’s growth chart and the normal growth chart can provide insights into the possible underlying disorders that could be responsible for the abnormal height.
Approach to the evaluation of height age
Measurement with a stadiometer
Serial height measurements plotted over time on the growth chart provide a key for the evaluation of the child’s height age. It also serves as the foundation for the treatment and diagnosis of growth-related abnormalities.
The best tool for measuring height accurately is a well-calibrated, wall-mounted ruler having a horizontal measuring bar fixed to it at 90 degrees. This device is called the stadiometer. Most parents and kids must have seen this device at the clinic of primary care physicians or pediatricians. A stadiometer can help to measure the child’s height more accurately.
The use of growth charts
Plotting the measurement of the child’s height on a growth chart is essential for monitoring his longitudinal progress in size. It can also help to assess the child’s height and weight versus the established normative ranges.
When plotted in a proper way, the growth chart can provide a snapshot of the child’s growth pattern over a period of time.
The growth charts exhibit the different patterns of growth depending on the height of the parents or any abnormality the child may be suffering from.
The patterns of growth charts include:
- A boy having tall parents and a constitutional taller stature.
- The growth pattern of a boy suffering from pathologic growth failure, with the cessation of the statural growth before the epiphyseal fusion has occurred.
- The growth pattern of a boy who has exhibited a constitutional delay in growth or puberty showing corresponding growth along the 5th percentile or the continued development after the expected phase of growth cessation.
Here are some factors you should keep in mind while applying the information obtained through these growth charts:
- Conventionally, the growth progression of the child over an extended period of time of at least 6 to 12 months is considered informative.
- It should be noted that though these growth charts are designed to help physicians assess the continuous as well as steady growths in children, the actual growth is reported to occur in gradual steps between frequent stops and starts.
- Also, the growth velocity of the child may vary in different seasons. It has been found that the growth of children usually accelerates in the summer and spring.
- The inferences derived from the growth chart of the child can be compared to his growth velocity to get a better idea of his height age or future growth and development.
- In children about 2 to 3 years of age, the deceleration in the spurious growth often seems to occur when the standing height is plotted on the supine chart as the standing height is always shorter compared to the supine length.
Hence, the supine length should be plotted only on the supine chart that is usually used for infants between the age of a few days to 3 years.
- Conversely, the standing height should be plotted only on the height chart that is used for children 2 to 20 years of age.
- For children who are born prematurely, the height and weight need to be adjusted for their gestational age before being plotted on the charts at least in the first 2 years of life.
The adjustment can be calculated by subtracting the number of weeks by which the child was born prematurely from the child’s present age (considering the 40 weeks’ gestation as the full-term birth).
So, the length of a 3-month-old infant (12 weeks of age) born at 34 weeks of gestation can be plotted at the point marking the 1.5-month (6 weeks of age), which is calculated as 12 weeks of age, minus the 6 weeks prematurity.
As the adult stature is usually determined genetically, the child’s future height potential may be calculated by using the mid-parental height.
The mid-parental height refers to the child’s estimated adult height calculated based on the heights of both the parents.
In boys, the father’s height is averaged with the mother’s height plus 5 inches or 13 cm while in girls, the mother’s height is averaged with the father’s height minus 5 inches or 13 cm.
The evaluation of the height age can be based on the ratio of the segments of the upper and lower body, especially in children who are growing below the 3rd percentile of height.
It can help to differentiate between conditions such as skeletal dysplasia that leads to disproportionate shortening of the limb and the disorders that primarily affect the spine like scoliosis.
The upper-to-lower body segment ratio can be calculated by measuring the lengths from the floor or symphysis pubis when the child is standing erect against a wall. This length provides the measurement of the lower body segment.
The length of the lower body segment can be subtracted from the child’s total height to obtain the measurement of the upper body segment.
The ratio can be derived by dividing the length of the upper body segment by that of the lower body segment.
Another accurate way for determining this ratio is to first measure the length of the upper body segment or the sitting height.
The sitting height can then be subtracted from the patient’s total standing height to get the value of the lower body segment.
These body proportions tend to vary during different ages of childhood.
The average ratio of the upper-to-lower body segment is about 1.7 at birth. It reduces to 1.0 by the age of 10 years as the legs grow in length.
These parameters help in the assessment of the child’s height age and provide a foundation for the diagnosis of any disorder that could affect his future growth.
The evaluation of the child’s height age and the future adult height
The disturbances in growth often manifest as the lower or higher absolute height and growth velocity.
The short stature can be defined as the height that is 2 standard deviations lower than the mean height for the specific age and sex (or less than the 3rd percentile).
A child may also grow to have a shorter stature if his height is more than 2 standard deviations less than the mid-parental height.
The growth velocity disorder can be defined as a very slow growth rate that may manifest as the deceleration in the height across 2 major percentile lines as plotted on the growth chart.
The short stature or slower growth is often the initial warning sign of a serious disease in the otherwise healthy-appearing child.
Hence, the evaluation of the child’s height age based on his growth trajectory plotted on the growth chart is essential for the early detection of these diseases.
A complete physical examination can help to differentiate between the abnormal growth pattern from the normal variants. It can also help to identify specific dysmorphic features linked to genetic syndromes.
For example; growth hormone deficiency occurring due to hypopituitarism might cause other signs and symptoms such as micropenis, midline defects, and midface hypoplasia.
Similarly, children with Cushing syndrome may exhibit signs such as obesity, violaceous striae, moon facies, and the cessation of linear growth.
Children with chronic renal failure may have pallor, edema, and ashen skin discoloration.
Severe hypothyroidism may cause an increased BMI due to the profound growth arrest coupled with the continued weight gain, delayed relaxation of the tendon reflexes, and sallow complexion.
Young Girls with Turner syndrome often present with a webbed neck, short stature, shield-shaped chest, or a low posterior hairline.
Continued evaluation of the child’s health based on physical examination, laboratory findings, and assessment by an endocrinologist can help in determining the impact of the child’s abnormal height age.
It can allow the physician to recommend a long-term treatment plan aimed at minimizing the complications linked to the genetic abnormality and provide support to ensure optimum growth and development with an aim to avoid the dysfunctions related to the vital organs.
This suggests that determining the height age of the child can not just help to manage the problems linked to his age but also help to improve the overall health.
Proper treatment of the child based on the underlying cause can restore the functions of the vital organs and reduce the risk of morbidities.
Tall stature can be defined as the height that is 2 standard deviations more than the mean for age and gender (higher than the 95th percentile). The excessive growth can be defined as the abnormally faster growth velocity that may manifest as height acceleration over at least 2 percentile lines on the growth chart.
Physicians should distinguish taller children who are otherwise healthy from those having underlying pathology. Most of the children whose height is more than the 95th percentile are a part of the normal distribution curve, while only a few are likely to have a defined abnormality.
However, the taller stature or increased height age or velocity could serve as the initial manifestation of an underlying disease like congenital adrenal hyperplasia.
As with short stature, a complete physical examination can help to differentiate the abnormal growth patterns from any non-pathologic variant in children with tall stature.
The measurement of body proportions is also essential for the differential diagnosis of growth acceleration and tall stature.
Children may demonstrate some clinical signs that could point to the particular underlying etiology.
For example, children with Klinefelter syndrome often have small and firmer testes while those with soft tissue overgrowth due to the increased growth hormone secretion may have coarse facial features, enlargement of the limbs, and mandibular prominence.
Height age provides vital clues to assess various aspects of the child’s health. It can help to determine the cause of tall or short stature. It can even help to detect diseases that can affect the functions of the vital organs.
This marks the importance of assessing the height age of children so that any abnormality can be detected at an earlier stage.