The authors describe the skin reflection measurement, obtained using a handheld optoelectronic device, to estimate gestational age of a newborn. The prototype unit of measurement and process of gestational age estimation were patented under number BR1020170235688 (CTIT-PN862) PCT\/IB2017\/056786 (WO2018083602). The Preemie-Test device was developed to detect the preterm newborns by analyzing the photobiological properties of the newborn's skin. This noninvasive and non-ionizing technology features a probe containing light emitters and receivers that is brought in contact with the newborn\u2019s foot and, using mathematical algorithms, provides an estimated dating within seconds The device provides automatic data acquisition with minimum operator influence and stores values in an electronic database. No values will be displayed on the device screen, thereby blinding the users to the results obtained at the time of acquisition.