Biological age of the child

Each child has an individual rate of biological development, and his biological age may differ to a certain extent from the age of his peers according to the birth certificate. We are talking about the individual biological clock of the body, which has a unique speed of running. This is such an important individual characteristic that even such powerful external synchronizers as the Sun, the Moon, the change of seasons, the change of day and night, are unable to neutralize it and subordinate it to the general rhythm of the flow of time. Many indicators of the functional capabilities of the body, its reactivity systems correlate primarily with biological age, but not with the calendar age. The peculiarities of the child's biological age are important for the adoption of an individual lifestyle, health protection, the use of different approaches to his upbringing and education. It is difficult to seat two friends of 6 years of age (according to the calendar) at the same desk and make the same demands on them if the biological age of one of them is 4, and the other is 8 years old. And this is often encountered in our schools.

Therefore, in the biology of childhood, attempts have been and are being made to classify periods of childhood not by calendar periods of life, but by essential biological features of maturity. Periodizations by prof. I. A. Arshavsky and G. Grimm have been published.

Classification of I. A. Arshavsky for the postnatal period of life

1. The neonatal stage of development is from birth until the end of colostrum feeding.
2. The period of lactotrophic feeding is before the introduction of thick complementary foods.
3. The period of combining milk feeding and complementary feeding is until the standing position is achieved.
4. Pre-school age - mastering locomotor acts. Formation of walking and running.
5. Preschool age - before the first permanent teeth appear.
6. Junior school age - until the first signs of puberty.
7. Senior school age - until completion of puberty.

An interesting aspect of the classification is the emphasis on the connection between developmental biology and the type of nutrition. However, the association is not always determined by the child's maturity level. It can be created arbitrarily. There is also a clear tendency to define the essence of the period, rather than the criteria for its selection.

Classification by G. Grimm

1. The neonatal period - until the umbilical wound heals.
2. Infancy - until the first milk tooth appears.
3. Nursery age - until children learn to walk.
4. Preschool age - until the first permanent tooth appears or the first eruptions are complete.
5. Primary school age - until the first sign of puberty.
6. Senior school age - until the completion of puberty.
7. The period of adolescence or girlhood - until optimal performance is achieved.

This classification is much more focused on the demarcation criteria of biological age periods. The disadvantage is the relative roughness of the division with excessively large age blocks.

Another variant of biological periodization could be this:

1. Pre-neonatal period (for premature or low birth weight babies) - up to a body weight of 2500 g and the formation of stable swallowing and sucking reflexes.
2. Neonatal period - until the physiological hypertonicity of the flexors of the upper limbs is relieved.
3. Early infancy - until the physiological hypertonicity of the limb flexors is completely relieved.
4. Late infancy - until walking without support or assistance.
5. Nursery age - until the milk teeth have completely erupted.
6. Pre-preschool - before obvious signs of the second period of milk bite (diastema - trema).
7. Preschool age - until the formation of a positive Philippine test.
8. Primary school age, or prepubertal age, is before the appearance of secondary signs of puberty.
9. Pubertal first (I-II stage of maturation according to J. Tanner).
10. Pubertal second (stage III-IV of maturation according to J. Tanner).
11. Pubertal third (stage V of maturation according to J. Tanner).
12. Age of maturity - from the completion of transverse growth (according to the measurement of the bitrochanteric and biacromial distances).

To determine the biological age of a child, an assessment of the development of such features that reflect new qualitative signs during the process of biological maturation or have a high degree of correlation with biological maturation is used. The simplest markers of biological age in adolescents can be signs or stages of puberty. In young children, biological age can be judged by the development and disappearance of the main reflexes of newborns, the formation of motor skills, and the appearance of baby teeth. In preschool age, an important sign of maturity is the appearance of permanent teeth. In special studies, biological age is determined radiologically, by the number of existing ossification points and nuclei. It is wrong to believe that bone age is a reflection of the true biological age of a child's body. This is the age of the skeletal system, depending on a combination of factors or conditions for the development of the musculoskeletal system. Other physiological systems can develop at a different pace and have other age characteristics.

Convenient reference points for tracking biological age can be the evolution of peripheral blood hemoglobin, the cytometric formula of lymphocytes, the formation of the a-rhythm of the electroencephalogram, etc. All anthropometric, physiological, metabolic, immunological signs of a healthy child that have clear and sufficiently vivid age dynamics or functional evolution can be used to judge the biological age relative to the calendar age. For this, it is necessary to have tables of age distributions of these signs, preferably presented in centile or nonparametric form. The biological age of the person being examined according to a given system (bone, cardiovascular, blood system, function of the renal tubular apparatus, etc.) will most likely correspond to the calendar age period when the obtained quantitative or dimensional characteristic of the organ (function) falls into the interval between the 25th and 75th centiles of the distribution. This indicates the most typical characteristics or properties inherent in 50% of healthy children of an age-sex group. In the absence of distribution tables, biological age can be roughly judged based on the maximum proximity of the selected quantitative characteristic to one of the average age values (arithmetic mean, median or mode).

The biological age of a child can be spoken of with certainty only if similar trends in magnitude and direction are revealed in a number of signs of maturity. Thus, the biological age of a child is the dominance of certain biological ages of individual tissues, organs and systems of the body. It can be presented in the form of the most frequent age or average biological age and some description of the identified fluctuations. This is the basis for judging the degree of harmony or disharmony of the child's growth and maturation, or, in the language of theoretical biology, the degree of heterochrony of development.

Heterochrony of varying degrees is inherent to every child, it is an integral property of the development process. Expressed disharmonisation with developmental delay (retardation, or bradygenesis) of some systems or developmental advancement (acceleration, or tachygenesis) of others creates critical states of functional adaptation and life activity with an increased risk of disease.

Of the anthropometric features that most closely correlate with biological age, one can point to body weight, chest circumference, and the ratio of the upper and lower body segments. A set of features that can be used to determine biological age is given in the chapter on physical development.

A very informative and valuable method for diagnosing biological age for pediatric practice is its integral assessment based on a large set of different age-specific features associated with different physiological systems. This approach has proven itself in perinatology, when significant discrepancies arise between the gestational age, anthropometric data of newborns and the characteristics of their biological maturity or age. The latter is significantly more significant for the probability of survival and preservation of the child's vital functions. Age in weeks of gestation is determined by the sum of points for 22 clinical features.

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Signs of biological maturity of a child

Signs	Points
1. Abdominal suspension
The head hangs down, the back is arched, the limbs hang straight	0
The head hangs down, the back is arched, the limbs hang almost straight	1
The back is slightly arched, the limbs are slightly bent	2
Head in line with straight body, limbs bent	3
The head is raised, the back is straight, the limbs are bent	4
2. Pulling up by the handles
The head lag is complete	0
Partial head lag	1
Absent	2
Head in front	3
3. Areola of the mammary gland
Absent	0
Up to 0.75 cm, smooth and flat, edges not raised	2
More than 0.75 cm, edges raised	3
4. Transparency of the skin on the abdomen
Numerous veins and venules are clearly visible	0
Veins and venules are quite distinguishable	1
Only a few large vessels are clearly visible.	2
Several large vessels are not clearly visible	3
Blood vessels are not visible on the skin of the abdomen	4
5. Down on the skin of the back
No gun	0
Abundant, long and thick hair all over the back	1
Thinning hair on the lower back	2
There is still fluff, but small areas without fluff are appearing.	3
Not on half the area of the back	4
6. Skin folds of the foot
There are no folds	0
Faint red streaks on the front of the plantar side of the foot	1
Distinct red stripes, indentations on less than 1/3 of the forefoot	2
Depressions over 1/3 of the forefoot	3
Deep, distinct creases over more than 1/3 of the forefoot	4
7. Labia
The large ones are open, the small ones protrude outward	0
The large ones almost completely cover the small ones.	1
The big ones completely cover the small ones	2
8. Testicles
Not a single one in the scrotum	0
At least one in the upper part of the scrotum	1
At least one in the lower part of the scrotum	2
9. Ear shape
The auricle is flat, shapeless, only parts of its edge are bent inward	0
Part of the auricle is bent inward	1
The entire top part is slightly curved inward.	2
All and clearly bent inward	3
10. Hardness of the auricle
The auricle is soft, bends easily and does not return to its original position.	0
The auricle is soft, bends easily and slowly returns to its original position.	1
The auricle has cartilage along the edge, is relatively soft, and after bending quickly returns to its original position.	2
Hard auricle, immediately returns to its original position	3
11. Mammary glands
Not palpable	0
Less than 0.5 cm in diameter	1
More than 1 cm in diameter	3
12. Square window
66-90°	0
56-65°	1
36-55°	2
11-35°	3
0-10°	4
13. Oblique elbow movement
To the axillary line of the opposite side	0
Between the midline of the body and the axillary line of the opposite side	1
Near the midline of the body	2
Doesn't reach the midline	3
14. Leg response
180°	0
90-180°	1
Less than 90°	2
15. Hand response
180°	0
90-180°	1
Less than 90°	2
16. Edema
Obvious swelling of the hands and feet, pastosity (dimples) above the tibia	0
Only dimples above the tibia	1
No swelling, no dimples	2
17. Popliteal angle
90°	5
90-100°	4
101-120°	3
121-140°	2
141-170°	1
170°	0
18. Pose
Full flexion of arms and legs	4
Legs are bent and spread apart, arms are slightly bent at the elbows	3
Arms and legs are extended	0
19. Heel - ear
Navel	4
Near the nipple	3
Collarbone	2
Chin	1
Ear	0
20. Backward foot bending
0-9°	4
10-20°	3
25-50°	0
55-80°	1
80-90°	2
21. Skin structure (hands and feet)
Very thin, gelatinous	0
Thin and smooth	1
Smooth, medium thickness, rash or superficial scaling	2
Thickening, superficial cracking and flaking, especially on the hands and feet	3
Parchment-like with superficial and deep cracks	4
22. Skin color
Dark red	0
Pale pink, relatively uniform	1
Pale pink, uneven	2
Paleness with pink coloration of the ears, lips, palms and soles	3

Score by total points

Total points	Biological age (weeks)	Total points	Biological age (weeks)
0-9	26	40-43	35
10-12	27	44-46	36
13-16	28	47-50	37
17-20	29	51-54	38
21-24	30	55-58	39
25-27	31	59-62	40
28-31	32	63-65	41
32-35	33	66-69	42
36-39	34

The norm, or the correspondence of biological age to the calendar age, to a certain extent indicates the well-being of the development and functioning of all the systems indicated. A lag in the biological age of body size and proportions may indicate the presence of pathological conditions or the inadequacy of the environment for the optimal development of the child.

Anthropometric indicators as a reflection of the biological age of the child

Here we have, on the one hand, a complete recognition by all researchers of the regular changes with age in many ratios of body lengths and diameters, and on the other hand, an almost complete disregard for the possibilities of practical use of these patterns for diagnosing the age of biological development of children. The latter is associated with the pronounced variability of body proportions, even in children of the same sex and age. Therefore, a sufficiently accurate diagnosis of biological maturation through body proportions is hardly possible without the development of special methodological techniques. At the same time, body proportions and their age dynamics could already be well used in monitoring the individual development of children, especially those with risk factors for deviations from normal growth and maturation. The development of standards for age-related body proportions in centile form could be the basis for determining the biological age of a child if there is a sufficiently wide range or set of such standards. If a number of body proportion indicators fall within the 50% zone (from the 25th to the 75th centile) of the same age group, then it can be considered that the child's biological age corresponds to the age of this group.

As proportions that could be standardized for determining biological age, it is necessary to list the index of the ratio of head circumference to height, already tested at the Research Institute of Hygiene of Children and Adolescents, as well as a number of indices calculated on the basis of the ratio of longitudes: the height of the upper part of the face relative to the length of the body; the length of the legs relative to the length of the body; the ratio of the upper and lower segments of the body.

The upper part of the face makes up about 16-18% of the body length in a newborn, and about 7-8% of the height in girls and boys.

The length of a newborn's leg is 36-40% of the body length, and by the age of 6-7 it can reach 52-55% of the height. The ratio of the length of the leg to the height of the upper part of the face has the widest range of age-related changes and can be calculated without converting the measurement data into percentages of the height of children.

Correlation analysis shows significant statistical relationships between the listed body proportion indices and such characteristics of children as dental formula, sexual development formula, physical performance and dynamometry indicators.

To diagnose the completion of the first extension, a number of authors recommend the so-called Philippine test. To expand the age limits of this test, it can be measured (in centimeters). Finally, in children of puberty, the anthropometric indicator of biological maturity can be the index ratio of two transverse diameters - interacromial (shoulder width) and intertrochanteric (pelvis width).

The methodology for using body proportions to assess biological age in the presence of centile age distributions can be as follows.

The first option - when all indices fall within the 25-75th centile zone, we can talk about the child's compliance with this biological age, when some of them go to the left or right - about a tendency to lag or advance the rate of biological development, when all measurements shift to the left or right in centile zones - about a certain lag or advance of development. In this case, it is possible to find an age centile scale, where the child's indicators will occupy a position between the 25th and 75th centiles, close to the median, and consider that the child's development (biological age) most closely corresponds to the age for which this coincidence is determined.

The second option is to determine the closest age median (50th centile) for each measurement or index and record the age to which this median relates, similarly the second, third index, etc. The biological age of a child can be calculated as the arithmetic mean of the written "ages" of its individual indices or measurements. The difference between the minimum and maximum age characterizes the severity of heterochrony, or disharmonisation, of development.

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