How do children grow taller? And what could possibly go wrong?

So how is it exactly that our body grows taller?

Our bones (especially our long bones and our vertebral column), have a layer of cartilage named a “growth plate”. Chondrocytes (cartilage cells) replicate within this space and form a complex process through which new cartilage becomes bone, and that is how our bones gradually grow longer.
Pediatricians who specialise in children’s growth tend to divide the possible causes of short stature in children into primary abnormalities (that occur within the growth plate itself), and secondary abnormalities (that occur outside the growth plate). This division is quite complicated and very hypothetical, and so I will not be going into it in this post.

Some examples of external factors that affect growth plates:
Growth hormone – this hormone is secreted from the brain’s pituitary gland (hypophysis) and causes the secretion of an additional hormone named IGF-1 in the liver and other target organs. The two of these provide support for longitudinal growth of the bone at the growth plate.
Other hormones that may affect the growth plate are the thyroid hormones, sex hormones and more.
Nutrition – children’s nutritional status greatly affects growth. This occurs through interaction with endocrinological factors such as leptin, IGF1, insulin, thyroid hormone and more.

When do children grow taller? And how tall do they grow?

Our bodies increase in 4 main stages. Each of these stages, or periods of time, has a different rate of growth and can be affected by different factors.
1. Prenatal period – the fetal period. Growth of the fetus is affected by 3 main factors: the mother, the placenta and the fetus itself. Any abnormality or interruption in these could harm growth. In contrast to the other periods of time, monitoring of the child’s growth rate is performed by a gynecologist. The average length of a child at birth is 50 cm.
2. Infancy – the first 2 years of life. Children grow about 25 cm in their first year of life, and around 12-13cm in their second year of life.
3. Childhood – starting age 2 and until puberty. In reality, this period of time is divided into two stages: age 2 – 6 or 7 years, when the expected rate of growth is 6-8cm/year and from 6 or 7 years till the beginning of puberty, when the expected growth rate is approximately 4-6cm per year.
4. Puberty – lasts around 3-4 years. During this period of time there is a significant acceleration in the rate of growth and the increase can reach up to 8-12cm per year. The acceleration is different in girls and boys. In girls, it happens at a younger age and at an earlier stage of puberty. Following acceleration, the rate of growth slows down until it stops. Growth stops when the growth plates close (in boys this happens at a bone age of approximately 17 years and in girls at 14.5 years).

How can we assess growth in children?

Firstly, with the help of quantitative measurements. These include weight, length (measured in lying position until the age of 2), height (measured in standing position starting age 2), BMI (mass in kg/height2in meters) and head circumference. There are additional measurements that can be taken by an endocrinologist such as upper to lower body segment ratio and arm span.
The quantitative measurements are plotted against growth charts so that the child’s growth percentiles can be described. One should always make sure that the correct charts are being used to suit the child’s age and gender. There are also custom charts such as for children born prematurely or children with genetic syndromes (for example Trisomy 21, Di-George, Russel-Silver, etc.).
When analysing the measurements and graphs we observe the child’s absolute weight as well as the rate of growth. So, if you are awaiting an endocrinology consult, I advise you to bring all the relevant documentation containing your child’s previous measurements that were carried out at the doctor’s office.

Is it possible to estimate my child’s final expected height?

When making an estimate of a child’s potential genetic height, we calculate the expected height by using the parent’s height (mid parental height). The calculation is as follows:
For boys (mother’s higher + father’s height+13)/2
For girls (mother’s higher + father’s height-13)/2
The disadvantage here is that the calculations do not take the child’s measurement into account, such as bone age, pubertal stage, etc., rather only the height of the parents.
Another option is to calculate the potential mature height according to the bone age (which can be determined based on a hand X-ray). We are familiar with the rates of growth that have been reached for each bone age, and we can use this value to calculate the final potential height (value to the power of 3). Note that this is not a very accurate method and the chances of making a mistake here can be very high.

Short stature in children – what height is considered short?

The definition of short stature is not consistent and is often debated. Some will say that short stature is defined as any height that is below the 10th percentile on the child’s growth chart, others will say that the border lies on the 4th percentile and some will say that it is any value that is at least 2 standard deviations below the average height as per gender and age (which is somewhere below the percentile 2.3).
Overall, it is important to take a look at the parents’ heights. If, for example, both parents are above the 80th percentile for height but the child’s height is around the 20th percentile, it is important to take note of this and perform a basic workup to make sure that there aren’t any medical factors that could be interrupting the child’s growth.

What is included in the initial evaluation for short stature?

The purpose of the workup is to rule out relatively common conditions that may cause short stature, some of which have already been mentioned in the above paragraph.

The blood tests include:
 Complete blood count – check for anemia, whether the while blood cells are high/low which may indicate an ongoing inflammatory process or immune deficiency, respectively.
 Full biochemistry panel – to check glucose levels, liver function tests, renal function tests, and parameters related to bone such as calcium, phosphate and more.
 Inflammatory markers such as erythrocyte sedimentation rate and c-reactive protein for a possible chronic inflammatory disease.
 Celiac serology, including IgA levels. Read more about Celiac’s here.
 Thyroid function tests – Ft4, TSH.
 First morning urine sample to check for specific gravity – this indicated the concentration of the urine as a screening test for a condition called Diabetes insipidus which could lead to growth impedance.

Hand X-ray for bone age: left hand X-ray can be performed to examine the growth plates and their level of ossification. Depending on the bone age and how consistent it is with chronological age, further investigation may be carried out. The investigation varies when there is a delay or advance in bone age compared to the chronological age. Additionally, the bone membrane can also be examined and presence of signs of skeletal dysplasia can be determined.

Secondary Assessment:
There are additional tests that can be performed, but if these are required, they are typically carried out after an endocrinology consult. These include
– Growth-hormone levels – expanding the laboratory workup to include additional hormones as well as performing tests and measuring growth hormone levels
– Karyotope
– Brain imaging
– Skeletal survey
– Genetic consult
And more…

What are the most common causes of short stature in children?

In about 75% of cases, the cause is one of two possibilities:
Familial short stature – my dear friends, if you look beneath an apple tree you will not find any oranges. Obviously, when both parents are relatively short, it is unlikely that their child turns out to be very tall. In these situations, the child’s height percentile will be similar to his parents’, their growth rate will be within normal limits, their initial evaluation will be normal and their bone age will match their chronological age.
Constitutional short stature – medically referred to as Constitutional Delay of Growth and Puberty or CDGP. These are the “late bloomers”, children that have a short stature all throughout their childhood but their growth rate is normal. Their hand X-ray reveals a delay in bone age while the remainder of their workup is normal. In children with CDGP puberty starts relatively late, and so does the acceleration in growth, and so they are usually shorter than the rest of the kids in their class who start growing before them. This pattern of growth is usually familial and when taking medical history, you will hear from one of the parents that they were short for a long time before catching up with their friends. In children with CDGP the final adult height is usually similar to that of the parents.

What other causes can there be to short stature?

Chronic illnesses – this entails about 10% of the causes of short stature. For example, Celiac – a very common condition in the general population that can sometimes manifest in a decrease in rate of growth, without any gastrointestinal symptoms (you can read more about Celiac’s here). Other examples are endocrinological conditions such as thyroid function abnormalities, chronic lung diseases such as cystic fibrosis, chronic kidney disease, inflammatory diseases (Crohn’s or Ulcerative Colitis), rheumatological diseases and more.
Genetic syndromes – these also represent about 10% of the causes. This category includes chromosomal abnormalities (such as Trisomy 21 and Turner’s), microchromosomal abnormalities (such as DiGeorge) and other genetic syndromes that are caused by minor changes in specific genes, such as CHARGE syndrome. Skeletal dysplasia – a disease that affects bones and causes growth abnormalities (and sometimes other abnormalities in different systems and organs), is also included here.
Growth hormone deficiency/resistance – these represent about 1-2% of the causes.
Children that were born small for gestational age (SGA) – we hypothesize that the underlying reason is a problem in these children’s growth mechanism, though medicine has been unable to put a finger on what it is exactly. Children that do not catch up and are still below the 3rd percentile for growth and height at the age of 4 can be offered treatment with growth hormone to prevent short stature at an older age (more about growth hormone to come).
There are certain rare conditions that can cause short stature such as Social Dwarfism – this can happen in children that suffer from emotional disabilities, abuse etc.

And once all other possible reasons are ruled out, we are left with a diagnosis that we refer to as “idiopathic short stature” (idiopathic – unknown reason). The height of children with idiopathic short stature is at least 2 standard deviations below the average and a detailed investigation fails to reveal any abnormalities. This is a diagnosis of exclusion. Nowadays, as available workup has extended to include genetic investigations in some of these children, the number of children that fall into this category is decreasing.

How shall we summarize this post?

Many different factors play a role in the process of growth in children. All these different factors need to work properly and appropriately to meet the child’s need to grow. Therefore, growth in a child is a good measure of generally good health.
If you are worried about your child’s growth, see your primary care physician first. He/she will take some measurements, compare it to previous measurements, plot them on a growth chart, ask you many different questions in search for a possible cause for growth problems, perform a physical examination and if need be, refer you to the initial workup that I mentioned above. After this initial evaluation, he/she will consider the need for an endocrinology consult and refer you to one accordingly.
What about the available solutions to these growth problems? Find out more here (coming soon).