Birth weight

At birth, the average weight of a human being varies from 3.2 to 3.4 kg.

Still on the basis of statistical data, when it comes to light, 90% of newborns record a variable weight ranging from 2.5 to 4.5 kg.

• A child of low weight is defined as having a body weight of less than 2, 500 grams at birth.
• A child of high weight or macrosomic is defined as the one who - at birth - has a body weight greater than 4, 500 grams (other authors consider a weight higher than 4, 000 grams high).

More correctly, birth weight should refer not so much to absolute values ​​as to the standards considered normal for the reference population, which take into account sex, race, duration of pregnancy and possibly other factors.

Here, then, in this perspective average weight at birth is defined as the 50th percentile, while the normal range extends between the tenth and ninetieth percentile. This latter limit corresponds to the value according to which 90% of newborns have a lower birth weight, while only 10% record higher weight values. Similarly, birth weight corresponding to the tenth percentile indicates that 90% of newborns have a higher birth weight, while only 10% have lower values.

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 the twins with respect to the single born.

At birth, the firstborn generally weigh less than the brothers.

Birth weight is influenced by the morphological characteristics of the parents; for example, the children of parents of high stature are generally longer and heavier at birth.

The chances of giving birth to a macrosomic newborn are significantly higher for diabetic, obese and / or mothers who are too fat during pregnancy.

The chances of giving birth to a low-weight baby are greater for mothers who have suffered from hypertension or heart problems during pregnancy, or have unconsciously used drugs, alcohol or cigarettes.

Within the low-weight category we can identify four groups of children:

LBW (Low Birth Weight) = low weight children, with a birth weight of less than 2, 500 grams;

VLBW (Very Low Birth Weight) = very low weight children, with a birth weight of less than 1, 500 grams;

VVLBW (Very Very Low Birth Weight) = very low weight children, with a birth weight of less than 1, 000 grams;

ELBW (Extremely Low Birth Weight) = children of extremely low weight, 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 the one that occurs before the 37th week of gestation, or before 259 days from the beginning of the last menstruation. When a child is born at a gestational age of less than 32 weeks, he is considered severely premature.

It should be noted, however, that not all preterm newborns are also of low weight: for example, a 36-week-old baby, therefore premature, can weigh 2, 600 grams, thus falling within the normal weight range. Furthermore, birth weight can be low but still appropriate for gestational age. Therefore, taking both factors into account, the newborn can be defined in three ways:

AGA (Adequate for Gestational Age): adapted to the gestational age;

SGA (Small for Gestational Age): small for gestational age;

LGA (Large for Gestational Age): great for gestational age

In the week following birth, there is usually a transient weight loss (5-10%, generally significant for macrosomic children and lower for underweight infants). This first phase is followed by a rapid weight gain, quantifiable at around 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 infants, while premature ones have different rates of growth.