FAMILIAL HEIGHT CALCULATOR
THE GENETIC GROWTH POTENTIAL THAT A CHILD HAS INHERITED FROM THEIR PARENTS CAN BE CALCULATED.
The family height estimate is not a growth forecast; it merely indicates the growth potential that may be inherent in the genes of both parents. When calculating the family height estimate, it should be noted that an average height difference of 13 cm between adult men and adult women is assumed
SIMPLE CALCULATION – SIMPLE FAMILY TARGET SIZE
In theory, a girl inherits:
- from her father, his height minus 13 cm
- from her mother, her height
In theory, a boy inherits:
- from his mother, her height plus 13 cm
- from his father, his height
If the child were to inherit the exact height from each parent, and if each parent’s height were to contribute exactly half to the child’s final height, then the following two calculation formulae would apply:
The formula for girls is:
Target height = (Father’s height – 13 cm)/2 + Mother’s height/2
The formula for boys is:
Target height = (Mother’s height + 13 cm)/2 + Father’s height/2
Or: (Mother’s height + Father’s height)/2 + 6.5 cm for boys = Tanner target height
(Mother’s height + Father’s height)/2 - 6.5 cm for girls = Tanner target height
This formula works worst when there is a significant difference in the parents’ heights. For example: both of a girl’s parents are 170 cm tall. The father is therefore rather short compared to other men, whilst the mother is rather tall for a woman. The mother has passed on her full height of 170 cm to her daughter via her genes. The father, who is also 170 cm tall, has passed on his ‘virtual’ female height of 157 cm to his daughter through inheritance, because if he were a woman, he would be 13 cm shorter.
Put simply, there are three possibilities when it comes to a daughter’s height: either she takes after her father or her mother, or she ends up being a mix of both parents.
The mother’s height, adjusted for gender,
so, in this example, 170 cm, because she’s a girl. She might have taken after her mother and inherited her height.
The father’s sex-corrected height,
so in this example 170 − 13 = 157 cm, because she is a girl. She could have inherited her father’s height.
The sex-adjusted heights of both parents divided by two
so in this example (157 cm + 170 cm)/2 = 163.5 cm, she could also have inherited an optimal combination of both parents.
For this reason, it makes sense to plot three different target heights on the growth chart. This allows you to see at a glance whether the child is likely to grow within the parents’ target height range.
MORE ACCURATE CALCULATION – CORRECTED FAMILY TARGET HEIGHT
The models set out above, which are designed to provide a reasonable estimate of inherited potential for final height, are simple to calculate; however, they produce a picture that is too extreme, particularly in the case of extreme values – that is, when the parents are very tall or very short. It has in fact been shown that many biological processes tend towards the middle, and this also applies to growth. On average, the offspring of very tall parents are shorter than one might expect based on the calculation models above.
The same applies to the offspring of very small parents. On average, these are less small than one might expect. This is taken into account in the Cole-Hermanussen formula. However, it can only be calculated using a calculator. The Cole-Hermanussen method allows a more accurate target size to be determined. This is closer to reality, but complicated to calculate.
cTHSDS = (father’s height in SDS + mother’s height in SDS) / 2 × 0.72
How the hereditary transmission of body height actually works in detail remains largely unknown. Calculations suggest that information determining final adult height must be located at at least four different sites in the genome.