Physiological (weight) loss of the newborn

After birth, the baby suffers a drop in weight that might seem excessive and alarming at first glance, so new mothers worry about it. The physiological decrease (or weight) of the newborn is instead completely normal.

From the moment it is born, the newborn must gradually  adapt to the surrounding world . He lived for nine months in a liquid, warm environment at a constant temperature where his little body only had to worry about growing using the energy his mother provided.

Once born, it is catapulted into a gaseous world where it has to start breathing on its own, with a percentage of oxygen 5 times higher than that of the mother’s uterus. Furthermore, it is a colder world and therefore it has to start to warm up on its own and the variable ambient temperature does not help it.

All this together with other small causes, leads to a natural weight loss in the first days after birth. We talk about physiological decrease or weight loss of the newborn.

Why does the newborn lose weight

During this adaptation phase, the child gradually loses fluids and adipose (fat) tissue. Furthermore, given that it feeds little in the first days of life, it does not compensate with nutrition for the expulsion of urine and faeces .

As a result, he loses weight.

This happens despite the fact that in the days immediately following birth the newborn feeds on colostrum from the mother’s breast, a substance very rich in nutrients and important for its development.

Colostrum, which sucks from the mother’s breast, despite providing the baby with all the nutrients it needs, fails to compensate for the weight loss due to the expulsion of urine and feces and therefore the baby eliminates more than it ingests.

However, this is completely normal.

As soon as the milk supply arrives to the mother, the baby will immediately start gaining weight.

What is the weight loss of the newborn?

Let’s quantify this neonatal weight loss to understand within what limits it is normal and when instead it can be a symptom of some problem.

Weight loss on the third day of life can reach 10% of birth weight.

So if a child is born weighing 3 kg, after 3 days he can weigh 2.7 kg (he has lost 300 grams). Compared to an adult weighing 50 kilograms, it is as if in three days he lost 5 kilos, an enormous amount.

Generally after 4-6 days the baby regains weight both because he starts feeding with complete breast milk and no longer just colostrum, and because his body has become accustomed to the change and has reached a certain balance.

When does it regain its initial weight?

The birth weight is usually regained on the tenth day and will have a steady increase from this point on (see growth curves).

The values ​​are in any case indicative because each child is different from the others and has its own particular rhythms, just as the mother may have the milk froth a little earlier or a little later than the average.

In the case of bottle feeding

Artificially fed babies generally have a lower weight loss and therefore a faster weight gain precisely because milk is available immediately and in pre-established doses.

In case of premature birth

Premature babies, on the other hand, can suffer a weight loss of more than 10% and recovery can last up to a month. In fact, their body is not 100% ready to face the outside world and therefore they will have greater difficulty and expenditure of energy to find balance (as well as having to complete the development that should have taken place in the belly).

Clearly it will be the pediatrician who will evaluate the variation in the weight of the newborn according to all conditions (birth weight, type of breastfeeding, premature birth, arrival of the milky flow, etc.), so there is no need to worry or get caught up in the Libra anxiety, anxiety that’s not good for either of you!

Kathryn Barlow is an OB/GYN doctor, which is the medical specialty that deals with the care of women's reproductive health, including pregnancy and childbirth.

Obstetricians provide care to women during pregnancy, labor, and delivery, while gynecologists focus on the health of the female reproductive system, including the ovaries, uterus, vagina, and breasts. OB/GYN doctors are trained to provide medical and surgical care for a wide range of conditions related to women's reproductive health.

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