At birth, the average weight of a human being ranges from 3.2 to 3.4 kg.
Also based on statistical data, when it comes to light, 90% of newborns register a weight ranging from 2.5 to 4.5 kg.
- A low-weight child is defined as one who, at birth, has a body weight of less than 2,500 grams.
- A child of high or macrosomal weight is defined as the one who - at birth - has a body weight greater than 4,500 grams (other authors consider a weight greater than 4,000 grams to be high).
More correctly, the birth weight should be referred not so much to absolute values, but to the standards considered normal for the reference population, which take into account sex, duration of pregnancy and possibly other factors.
Birth weight: did you know that ...
At birth, a male infant weighs on average about 150-200 grams more than a female infant. The same goes for twins compared to single births.
At birth, firstborns generally weigh less than siblings.
Birth weight is influenced by the morphological characteristics of the parents; for example, children of tall parents are generally longer and heavier at birth.
The chances of giving birth to a macrosomal infant are much higher for mothers who are diabetic, obese and / or who have gained too much weight during pregnancy.
The chances of giving birth to a low weight baby are higher for mothers who have suffered from high blood pressure or heart problems during pregnancy, or have subconsciously used drugs, alcohol or cigarettes.
Within the category of low-weight births we can identify four groups of children:
LBW (Low Birth Weight) = children of low weight, with a birth weight of less than 2,500 grams;
VLBW (Very Low Birth Weight) = children of very low weight, with a birth weight of less than 1,500 grams;
VVLBW (Very Very Low Birth Weight) = children of very very low weight, with a birth weight of less than 1,000 grams;
ELBW (Extremely Low Birth Weight) = extremely low weight babies with a birth weight of less than 750 grams.
In most cases, low birth weight babies are premature babies. The World Health Organization (WHO) defines preterm birth as that which occurs before the completed 37th week of gestation, that is, before 259 days from the date of the start of the last menstruation. When a baby is born at a gestational age of less than 32 weeks, is defined as severely premature.
It should be noted, however, that not all preterm infants are also of low weight: for example, a 36-week-old infant, therefore premature, can weigh 2,600 grams, thus falling within the normal weight range. Furthermore, birth weight can be low but still adequate for gestational age. Therefore, taking into account both factors, the newborn can be defined in three ways:
AGA (Adequate for Gestational Age): suitable for gestational age;
SGA (Small for Gestational Age): small for gestational age;
LGA (Large for Gestational Age): large for gestational ageIn the week following birth, there is usually transient weight loss (5-10%, generally significant for macrosomal babies and less for underweight infants). This first phase is followed by a rapid weight gain, quantifiable in about 150/200 grams per week during the first five months, which leads to a doubling of the birth weight by the end of the fifth month of life. Of course, these values refer to full-term babies, while premature babies have different growth rates.
