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Fetal Echo Z-Scores

Z-scores for fetal cardiac measurements using gestational age, BPD, femur length, or head circumference (Lussier 2020)

For educational and informational purposes only. Verify all results before clinical application.

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References

  1. Lussier EC, Yeh S-J, Chih W-L, et al. Reference ranges and Z-scores for fetal cardiac measurements from two-dimensional echocardiography in Asian population. PLoS ONE. 2020;15(6):e0233179.[DOI]
  2. Schneider C, McCrindle BW, Carvalho JS, et al. Development of Z-scores for fetal cardiac dimensions from echocardiography. Ultrasound Obstet Gynecol. 2005;26(6):599-605.[DOI]

Reviewed by Daniel Diaz-Gil, MD · Last updated March 2026

Medical disclaimer

This tool is for educational and informational purposes only. It is not a substitute for professional clinical judgment. Always independently verify results before making clinical decisions.

Professional Resources — Tools used by pediatricians for cardiac assessment

Park's Pediatric Cardiology for Practitioners, 7th EdComprehensive reference for pediatric cardiology evaluation and management~$95via AmazonEchocardiography in Pediatric and Congenital Heart Disease, Lai et alDefinitive echo reference with z-score tables and imaging protocols~$180via AmazonBoardVitals Pediatric Cardiology QbankBoard-style questions for pediatric cardiology certificationsubscriptionvia BoardVitals
Clinical Reference & Evidence

Fetal Echocardiographic Z-Score Calculator

Overview

This calculator provides z-scores for 13 fetal cardiac structures using regression equations from Lussier et al. 2020, derived from 575 healthy Asian fetuses (gestational age 14-38 weeks). Measurements can be normalized against five developmental markers: estimated gestational age (EGA), biparietal diameter (BPD), femur length (FL), abdominal circumference (AC), or head circumference (HdC).

What It Measures

Heart dimensions: Heart width, heart length, heart circumference, heart area, chest circumference

Chamber widths: Left atrium, right atrium, left ventricle, right ventricle

Great vessels: Aortic annulus, pulmonary annulus, transverse aortic isthmus, transverse ductus arteriosus

When to Use

  • Prenatal screening for congenital heart disease
  • Assessment of cardiac structural abnormalities detected on routine obstetric ultrasound
  • Monitoring fetuses with known risk factors (family history, maternal diabetes, teratogen exposure)
  • Serial surveillance of fetuses with suspected cardiac pathology
  • Prenatal counseling and planning for delivery and postnatal management

Developmental Markers

  • EGA (weeks): Best overall correlation for heart size parameters (HW, HL, HtC, HA, CC), LV, and aortic annulus
  • Head circumference: Optimal for predicting LA, RA, RV, PA, and ductus arteriosus dimensions
  • BPD, FL, AC: Alternative markers when EGA is uncertain

The study found that estimated gestational age was generally the best predictor for overall fetal cardiac development, while head circumference was optimal for certain chamber and vessel dimensions.

Interpretation

Z-Score Range Classification
-2 to +2 Normal fetal cardiac dimension
-3 to -2 or +2 to +3 Borderline - further evaluation recommended
< -3 or > +3 Abnormal - specialist referral indicated

Key Clinical Points

  • Z-scores use the Schneider method: Z = (ln(actual) - ln(predicted)) / RMSE
  • Most structures have linear relationships with developmental markers
  • The aortic isthmus (by EGA) uses a quadratic model
  • Some structures use natural-log transformed equations (pulmonary annulus by EGA, ductus arteriosus by EGA)
  • All measurements in centimeters (except heart area in cm2)

Limitations

  • Derived from a Taiwanese population; may not generalize to all ethnicities
  • Sample size of 575 fetuses with single-observer measurements
  • Some structures (aortic isthmus, ductus arteriosus) have lower R-squared values, yielding less precise z-scores
  • Does not include ventricular wall thickness, bilateral PA diameters, or sagittal aortic isthmus measurements
  • Fetal measurements are inherently more variable than postnatal due to fetal position and image quality

Reference

Lussier EC, Yeh S-J, Chih W-L, et al. Reference ranges and Z-scores for fetal cardiac measurements from two-dimensional echocardiography in Asian population. PLoS ONE. 2020;15(6):e0233179. DOI: 10.1371/journal.pone.0233179