About this App

"z-scores have ... become invaluable for tracking longitudinal changes of growth for individual patients and for comparing changes in growth of cardiac structures for different fetal populations."

— Hornberger LK., Ultrasound Obstet Gynecol. (2010)

This site represents my effort to collect and adapt some of the most recent data as it pertains to calculating z-scores for fetal echocardiography. This site hopefully improves on my previous attempts to do the same. You can now:

  • calculate z-scores based on any of several independent measures (ega, femur length, or biparietal diameter)
  • see all of the available z-score references for any given site
  • view generated reference-values graphs

The included references were selected because they:

  • used modern imaging equipment
  • used standardized (guideline?) measurement techniques
  • provided data that I could use—explicitly—to generate a z-score

While I call this a web app, I mostly mean that it is a web site that is useful on a wide variety of devices and screen sizes—it is not a native app that you can download.


About Z-Scores

According to the American Society of Echo's Recommendations for Quantification Methods During the Performance of a Pediatric Echocardiogram:

When normative data are available, the measurements of cardiovascular structures should be expressed as Z scores

A z-score indicates:

how many standard deviations an observation is above or below the mean. It allows comparison of observations from different normal distributions, which is done frequently in research.

(See the Wikipedia entryfor more information about z-scores.)

Concerning the application of z-scores to pediatric cardiology, interested persons should read:

About Me

My name is Dan Dyar.

Among many other things, I am a Pediatric Cardiac Sonographer. Having worked in this field since Before The Internet, I sometimes observe the collision of technology and information in this field and am astonished by the disparity: we are simultaneously incredibly advanced and desperately primitive.

I hope this website helps soften these collision.

Contact Me

Fill out the form here and I'll get back to you as soon as I can.


While I mostly do this as a hobby, and I try to operate within the "free tier" of App Engine and Amazon Web Services, that is not to say that this is an entirely expense-free occupation.

If you would like to help support the development of this and other projects, please consider making a donation to my PayPal account:

Change Log

10 Feb 2019: v.0.35

  • adds z-score for cardiac outputs per Rocha et al.; shout out to user "Lisa V." for the inspiration :)

14 Jan 2019: v.0.34

  • adds z-score for outflow tracts per Vigneswaran et al.; shout out to user "Anne" :)

03 Sep 2017: v.0.33

  • corrects z-score for RV Major per McElhinney et al.; shout out to user "Ruth K" :)

25 Nov 2016: v.0.32

  • adds Krishnan et al. data using EGA, FL, BPD

13 Mar 2016: v.0.31

  • adds Gagnon data for M-Mode and Doppler

27 Dec 2015: v.0.3

  • adds Gabbay-Benziv data for LV minor, RV minor

28 Mar 2012: v.0.2.5

  • modified start page text/instructions

24 Mar 2012: v.0.2.4

  • added ratio calculations(issue#2)

24 Mar 2012: v.0.2.3

  • added mini-chart/styles/mediaquery for handhelds

23 Mar 2012: v.0.2.2

  • added link to '/app#biometry' on missing independent value error

23 Mar 2012: v.0.2.1

  • added changelog
  • added paypal button (by request)

22 Mar 2012: v.0.2

  • added datastore

21 Mar 2012: v.0.1

  • initial roll-out