The fetal echo z-score calculator was initially a proof-of-concept project (as were all of the calculators at ParameterZ.com). It has since proven itself to be quite useful, and I refer to it for nearly all fetal echos now.
However, a shortcoming of the current calculator is highlighted by this common referral:
- SGA (Small for Gestational Age)
- RV > LV
- LV measures lower limits of normal for EGA
The real difficulty here of course, is the SGA baby. Based purely on dates, the baby is known to be small- and all measures of her cardiac structures are sure to be small as well.
Absolutely.
Small.
But can't her heart still be relatively normal ?
In the article Development of Z-scores for fetal cardiac dimensions from echocardiography, regressions are presented based on three independent variables: femur length, biparietal diameter, and EGA. According to the authors, "femur length gave the better correlation coefficient with fetal cardiac dimensions" though admittedly, all the independent variable gave good correlations. And a good discussion is made over EGA as a surrogate for fetal size, the importance of considering fetal size, fetal growth and fetal size, fetal size, fetal size, ...
So why don't I build the calculator based on the femur length- ergo the fetal size?
Because: I have now become an advocate of measuring the fetus:
- measuring the BPD
- measuring the head circumference
- measuring the abdominal circumference
- measuring the femur length
Now, I measure the fetal size and, taking advantage of the OB calculation package on the ultrasound machine, use the size-determined EGA- rather than the date-determined EGA.
The new and improved fetal echo worksheet allows you to edit the EGA and automatically update all of the z-scores based on your measurements. And, just for fun, makes estimations of the EDC and LMP.
