Assessment of postnatal gestational age using sonographic measurements of femur length.

Abstract

Assessment of gestational age in the premature newborn infant is both essential and difficult. The purpose of this study is to evaluate a new method for the assessment of gestational age in premature neonates using femur length measurements obtained by ultrasonography and compare these with an established clinical method. Forty-seven newborn infants with true gestational age calculated by reliable last menstrual period, further confirmed by obstetric ultrasonographic estimation performed at <18 weeks, were enrolled within 3 days of birth. Birth weight, length, and head circumference were appropriate for the true gestational age. The modified Ballard maturational scoring system was used to determine gestational age. A trained sonographer imaged the femur and measured the shaft of the femur using electronic calipers. Gestational age was estimated from an average of six femur length measurements by a radiologist blinded to the study using tables of fetal femur length measurements. Results indicate that gestational age assessment by ultrasonography has an excellent correlation with true gestational age (r = 0.93), as does assessment by the Ballard score (r = 0.87), with no statistical difference between both the correlations' coefficients. We conclude that gestational age assessment in newborn infants weighing <1500 g, without intrauterine growth retardation, by sonographic measurement of femur length is an excellent means to estimate true gestational age. Furthermore, the sonographic method is ideal for sick, paralyzed neonates and may be useful in the design of future clinical trials.