Physiological variations in the pigmentation of newborn infants.

Skin pigmentation is a physiological feature of great value and usefulness from both an anthropological point of view and a clinical point of view. This article is a first approach to the study of the skin pigmentation of 126 full-term newborn infants (37-42 weeks gestational age) at the Maternity Hospital "La Paz" (Madrid, Spain) using the reflectance method. We provide the normal patterns, which have to be taken into account when applying this method to detect transcutaneous bilirubin and some physiopathological conditions, such as hyperbilirubinemia, anemia, plethora, and hormonal disturbances. Measurements of the reflectance were taken at the forehead, the internal and external aspects of the arm, the thorax, and the gluteus with blue, green, and amber tristimulus filters. With all filters the least pigmented zone was the thorax, and the most pigmented zone was the forehead; the internal aspect of the arm, the gluteus, and the external aspect of the arm were intermediate in increasing order. Our data confirm a higher pigmentation at birth than during the first year. We think that the idea of cephalocaudal progression of hyperbilirubinemia must be rejected. Our results also indicate that the thickening of the skin with gestational age is one of the most important factors in the skin color changes of newborn infants with an apparently different rhythm in males than in females.