What does the harlequin sign indicate in a newborn?

The harlequin sign is characterized by an asymmetric change in skin color, where one side of the newborn's body appears red while the other side takes on a pale appearance. This phenomenon is most commonly attributed to an immature autonomic nervous system. The autonomic nervous system plays a critical role in regulating blood flow and skin perfusion; during periods of unstable regulation, such as in premature or underdeveloped infants, fluctuations in skin temperature and color can occur.

In this context, the harlequin sign highlights the vulnerability of the newborn's circulatory control mechanisms rather than indicating any severe medical conditions like dehydration, congenital heart disease, or respiratory distress. These latter conditions typically present with more systemic or generalized signs that are not limited to localized skin color changes. Understanding the harlequin sign as a sign of an immature autonomic nervous system helps caregivers monitor and assess the development of neonatal neurological function.