Table 4

Diagnostic accuracy of Ballard, LMP and AMANHI models for identification of newborns <37 and <34 weeks (gold standard dated by early pregnancy ultrasound)

ModelArea under the curveCut-off selectionSensitivitySpecificityPositive predictive
Negative predictive
Positive likelihood ratioNegative likelihood ratio
Classify <37 weeks*
 LMP (<37 weeks)†0.81LMP <37 weeks cut-off0.690.810.220.973.720.38
 LMP0.8180% sensitivity0.800.710.180.982.780.28
 Ballard exam‡0.74BS cut-off <37 weeks0.090.980.250.934.290.93
 Ballard exam0.7480% sensitivity0.800.520.120.971.680.38
 Model A (10-characteristics)0.8880% sensitivity0.800.800.230.983.930.25
 Model B (10-characteristics+LMP)0.9180% sensitivity0.800.870.320.985.960.23
 Model C (BW+LMP)0.8880% sensitivity0.800.800.230.983.950.25
 Model D (BW+HC)0.8480% sensitivity0.800.720.180.982.850.28
Classify <34 weeks§
 LMP¶0.94LMP <34 weeks cut-off0.610.950.101.0012.930.41
 LMP0.9480% sensitivity0.800.900.
 Ballard**0.89BS cut-off <34 weeks0.031.000.400.9974.360.97
 Ballard0.8980% sensitivity0.800.810.
 Model A (10-characteristics)0.9480% sensitivity0.800.960.161.0021.380.21
 Model B (10- characteristics+LMP)0.9680% sensitivity0.800.980.311.0050.390.20
 Model C (BW+LMP)0.9680% sensitivity0.800.980.231.0034.240.20
 Model D (BW+HC)0.9380% sensitivity0.800.930.101.0012.230.21
  • Diagnostic accuracy for different cut-offs with preset sensitivity of 85%, 90% and 95% are shown in online supplemental table 2.

  • *In the cohort there were 536 infants that were classified as preterm <37 weeks, and 6892 classified as ≥37 weeks.

  • †LMP <37 weeks was classified as preterm, and LMP ≥37 weeks classified as full term.

  • ‡GA as determined by Ballard score was classified as preterm if GA <37 weeks using the equation GA=((2×score)+120))/5.

  • §In the cohort there were 66 infants that were classified as preterm <34 weeks, and 7362 classified as ≥34 weeks.

  • ¶Threshold of GA determined by LMP <34 weeks.

  • **Original Ballard score equation (as per footnote 3) classification.

  • AMANHI, Alliance for Maternal and Newborn Health Improvement; BS, Ballard Score; BW, birth weight; GA, gestational age; HC, head circumference; LMP, last menstrual period.