Objective: The New Ballard Score (NBS) has been evaluated only until 96 hours of age. We studied the validity and reliability of NBS for gestational age (GA) assessment on days 1, 5 and 7 of postnatal age (PNA). Design and setting: This prospective, analytical study was conducted in a level III neonatal unit.
Patients: Neonates born at a GA of 29-35 wks (based on accurate LMP) were eligible. Encephalopathy, malformations, and unstable vitals were exclusion criteria. LMP-based GA was the gold standard. NBS was assessed within 24 hrs of birth by one rater and two raters assessed NBS on days 5 and day 7. All were blinded to LMP and each other's ratings. Recruitment continued until >100 subjects were enrolled with >25 in each LMP-based GA group: 29-30 wks, 31-32 wks, 33-34 wks and 35 wks.
Main outcome: Correlation of GA assessed on day 7 with gold standard.
Results: 129 neonates were studied. NBS-based GA on days 5 or 7 did not differ from the gold standard GA by more than 2 weeks in any subject. On day 7, NBS over-estimated GA in 26.7% and under-estimated in 19.8% cases; all discrepancies being <2 wks. Compared to gold standard GA, the intra-class correlation (ICC) of the NBS-based GA of the day 1 rater, day 5 rater and day 7 rater were 0.94, 0.94 and 0.92 respectively. ICC for inter-rater reliability on day 5 and day 7 were 0.97 and 0.96 respectively. Compared to the day 1 rater's raw NBS, the ICC of day 5 and day 7 raters' total scores were 0.98 and 0.97; of day 5 and day 7 raters' neurological scores were 0.98 and 0.97; and of day 5 and day 7 raters' physical scores were 0.92 and 0.88. All ICC's mentioned above had p values <0.001.
Conclusions: NBS is a valid and reliable clinical tool for GA assessment until day 7. It slightly over-estimates the GA with increasing postnatal age. Neurological signs are more reliable than physical ones.