Weight gain
also see Height gain, Birth Weight

Estimating weight: 1/2 month + 3.5 kg  or 2(year) +12 kg

Different organs grow at different rates. For instance, the reproductive system has a brief growth spurt just after birth, then changes very little until just before puberty. In contrast, the brain grows almost exclusively during the early years of life. At birth, the brain is one fourth of its future adult size. By 1 year, the brain is three fourths of its adult size. The kidneys function at the adult level by the end of the first year.