Background and objectives: The New Ballard Score (NBS) is commonly used to estimate gestational age (GA) in the newborn. The aims of this study were: a) to determine the reliability of the NBS; b) to estimate the agreement between two methods of GA assessment, NBS and ultrasonography (US) or last menstrual period (LMP); c) to estimate the agreement between NBS and US/LMP in distinct subgroups of neonates.
Patients and methods: We performed a prospective, blind study. NBS was performed in neonates born in Hospital 12 Octubre, Madrid before the age of 48 hours. The level of agreement was estimated with two analytical parameters: the intraclass correlation coefficient (ICC) and the mean differences method (MD).
Results: Inter-observer agreement was very good (ICC > 0.8). Agreement between US/LMP and NBS was good (ICC = 0.6-0.8). In infants with lower weight or GA, and in those whose mothers had received prenatal corticosteroid therapy, NBS tended to overestimate GA compared with US/LMP (MD = 1.2-2.9).
Conclusions: The agreement between two observers in NBS assessment was very good. The agreement between NBS and US/LMP was good, but differences of more than 2 weeks in GA were frequent. In very preterm newborns and in infants whose mothers had received prenatal corticosteroid therapy, NBS tends to overestimate GA.