Is there a standard for determining gestational age score that falls between the score sheet guidelines?

My exam total score is 27, which falls between the 25 and 30 point scores. Do I assign 34 weeks or 35 weeks, and why?..

For scores between numbers on the grid, we interpolate as follows:

  • 25 = 34 weeks
  • 26 = 34 weeks
  • 27 = 34 weeks
  • 28 = 35 weeks
  • 29 = 35 weeks
  • 30 = 36 weeks

The reason we interpolate this way is that we wish to record only completed weeks of gestation and not partial weeks. In addition, this assessment is a clinical one and to record partial weeks would result in false accuracy, since maternal ovulation varies several days among women.

Therefore, we interpret the results of the gestational assessment as follows:

  • If weeks by exam fall within 2 weeks of KNOWN maternal dates, preferably confirmed by early ultrasound, then the maternal dates are more likely correct.
  • If weeks by exam are greater than 2 weeks outside of maternal dates in either direction, then the clinical gestational assessment is more likely correct.

Dr. Ballard

References :
Ballard JL, Khoury JC, Wedig K, et al: New Ballard Score, expanded to include extremely premature
infants. J Pediatrics 1991; 119:417-423.