Estimation of gestational age by the length of the dorsal spine

Gestational age assessed by dorsal spine length (DSL) was compared with that based on date of the last menstrual period (LMP). This study was performed in 70 newborn infants admitted to a neonatal intensive care unit requiring chest radiography, by which dorsal spine length was measured (figure 1). Gestational age ranged from 23 to 42 weeks. Regression analysis were performed on DSL and gestational age. Estimation error was evaluated based on the percentage of agreement in weeks (validity) and the difference in averages between both methods (accuracy) (table I and figure 2). Variations during the first week of life were also studied and no significant differences were found. For infants born at 31 weeks or less, DSL overestimated gestational age in one week. There was no differences between 32 and 36 weeks, and over 37 weeks, underestimation was one week (figure 3). With this correction a table was built estimating gestational age for different DSL; percentage of agreement was 91.4% for +/- 3 weeks (table III). This methodology assists the clinician to evaluate gestational age by an objective method, that does not vary during the first week of life and that can be obtained retrospectively.