Birth weight
A full-term newborn has an average birth weight of about 3200 - 3400 grams; the interval of normality - necessarily wider - is instead included between 2500 and 4500 grams, while outside these limits we speak respectively of a newborn with low or high birth weight.
To learn more: birth weight
Baby Weight Growth
In the first few days of life, the weight of the newborn tends to fall by 5-7%, due to stress induced by childbirth and the various processes of adaptation to the new environment. If well fed, the newborn recovers the lost weight by the 15th day of life; in this period, up to about the sixth month, the average weight growth rate is around 150 grams per week. Therefore, by the fifth month, birth weight is normally doubled.
To learn more: weight growth of the newborn.
Growth up to adolescence
During the first year, birth weight is almost tripled, while the length increases by about 50%.
| Months | Weight males | Females weight |
| 18 | from 9.0 to 13.6 Kg | from 9.8 to 12.8 Kg |
| 19 | from 9.8 to 13.7 Kg | from 9.1 to 13.0 Kg |
| 20 | from 10.0 to 13.9 Kg | from 9.2 to 13.2 kg |
| 21 | from 10.1 to 14.2 Kg | from 9.4 to 13.4 Kg |
| 22 | from 10.3 to 14.3 Kg | from 9.5 to 13.6 Kg |
| 23 | from 10.4 to 14.6 Kg | from 9.7 to 13.8 Kg |
| 24 | from 10.6 to 14.8 Kg | from 9.8 to 14.1 Kg |
Subsequently, weight growth continues, albeit in slow motion. Around the 18 months, in particular, the weight increase of the child is significantly reduced compared to the previous periods. If, from birth to half a year, the baby increases its weight to 10-11 kg, from 18 months to 2 years the increase is around a kilo.
The physiological "stop", therefore, must not alarm: it is not a permanent block of growth, but a decrease in the increase.
At around two years of age, birth weight is approximately fourfold, while stalemate in weight growth continues up to 5 years; during this three-year period, in fact, the weight of the child increases just under 2 kg per year. At the age of five, the rate of weight growth gradually increases, up to around 2.4 kg at the onset of puberty.
The weight trend is uneven compared to that of height, so much so that around 6 years of age there is a physiological increase in BMI. The earlier this reversal is, the greater the risk of the child becoming obese in adolescence and adulthood (for more information: adiposity rebound).
The hormonal upheaval that accompanies puberty is associated with a lively revival of the growth rate of weight, which is integrated - according to a harmonious alternation - with the statural growth.
Normal weight growth
Reference values for full-term newborns with normal weight
| Birth | Male 3400 grams; Female 3200 grams |
| 5th month | Birth weight doubles |
| 12th month | Birth weight triples |
| 24th month | Birth weight quadruples |
| After the 2nd year up to the 10th | The weight is given by the formula: age (years) x 2 + 8 |
The summary table shown in the table shows the average weight growth of infants and children. Obviously, within the population there are important and absolutely physiological variations. If the child does not show substantial changes in the sleep / wake rhythm, mood, appetite, concentration and evacuates regularly, it is very likely that any alteration in weight growth will be benign.
Of course, to express an opinion about a possible excess or weight defect, the pediatrician will have to make use of specific indexes, which take into account not only the chronological age, but also the statural one. An optimal evaluation of body fat, however, can only be achieved through instrumental investigations such as plicometry and bioimpedance analysis.
Growth percentages
| Percentiles of weight growth (newborn) | |
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| Weight growth percentages (children) | |
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- the age is selected for which the measured height of the child corresponds to the 50th percentile;
- from the point obtained, a perpendicular line is drawn, detecting the weight value corresponding to the 50th percentile; the ideal weight is thus obtained.
 | See example |
- overweight, if the excess weight is between 10 and 20% more than the ideal weight;
- obese, if the excess weight is 20% higher than the ideal weight;
- superobeso, if the excess weight is 50% higher than the ideal weight;
- lean, if the weight defect is more than 15% compared to the ideal weight.
