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Biparietal Diameter (BPD)

Data sources

  • INTERGROWTH-21st: Provides international fetal growth standards for biparietal diameter in millimeters.
  • Centile tables (3rd-97th):contentReference[oaicite:0]{index=0}.
  • Z-score tables (-3 SD to +3 SD).
  • NICHD: U.S.-based, multi-ethnic cohort; percentiles stratified by maternal race/ethnicity.

Mapping strategy

  • Look up the expected BPD at given gestational age in weeks.
  • Convert observed value into z-score or percentile.
  • Apply cutoffs (e.g., <10th percentile = small for gestational age).

Planned extensions

  • Compare performance between NIHCD and INTERGROWTH references.
  • Add crosswalk functions so users can explicitly choose the reference standard.