Neonatal jaundice is very common and in most cases is a physiological process rather than a pathology. This is related to the peculiarities of bilirubin metabolism in newborns and the adaptation of the liver after birth.
During intrauterine life, the child predominantly has fetal hemoglobin (HbF), which is rapidly destroyed after birth, being replaced by "adult" hemoglobin (HbA).
With the mass breakdown of red blood cells, a large amount of bilirubin is formed. The newborn's liver is still functionally immature and cannot quickly conjugate (bind) bilirubin to eliminate it from the body.
The level of unconjugated bilirubin in the blood increases, which colors the skin and mucous membranes yellow.
The role of sunlight and why "window" or walking helps. Sunlight (especially in the blue-green spectrum range) initiates the process of photodestruction of bilirubin.
Under the influence of ultraviolet and visible rays, unconjugated bilirubin is converted into water-soluble isomers (lumirubin), which can be excreted through the liver and kidneys without the involvement of the liver's enzymatic systems.
This is the principle of phototherapy, which is used in maternity hospitals and clinics, only with the use of lamps of a specific wavelength (usually 460–490 nm).
"Jaundice" usually resolves on its own. In most newborns, physiological jaundice develops on the 2–3 day of life, peaks at 4–5 days, and gradually decreases by the 10–14 day, when the liver matures and begins to actively conjugate bilirubin.
Sufficient breastfeeding and sunlight accelerate the elimination of bilirubin.
It is important to distinguish between physiological and pathological jaundice. If jaundice appears within the first 24 hours after birth, persists for more than 2–3 weeks, is accompanied by high bilirubin concentration, lethargy, refusal to eat, or changes in stool/urine color — this may be a sign of a pathological condition (hemolytic disease, infection, liver or biliary tract pathology) and requires medical monitoring.
