Obstet Gynecol Sci.  2016 Mar;59(2):91-96. 10.5468/ogs.2016.59.2.91.

Simple mathematical formulae for estimation of median values of fetal biometry at each gestational age

• Choi HY
• Kim JH
• Park JY
• Jung EY
• No JH
• Oh KJ
• Hong JS

• KMID: 2159002
• DOI: http://doi.org/10.5468/ogs.2016.59.2.91

Abstract

OBJECTIVE
The aim of this study was to propose simple mathematical formulae to estimate median values of fetal biometry including biparietal diameter (BPD), abdominal circumference (AC) and femur length (FL) at each gestational age (GA) easily without looking up the previously established reference values.
METHODS
Simple mathematical formulae to estimate median values of fetal biometric values at each gestational week were inferred. To validate these formulae, three different linear equations were derived from previously reported reference values of median BPD, AC and FL using regression analysis at each gestational week. Finally, calculated data through the inferred formula were compared to retrospectively collected data (observed data).
RESULTS
The equation revealing the relationship between BPD and GA was: median BPD (cm)=GA (wk)/4. Using this simple mathematical formula, the absolute percentage error between observed data and calculated data ranged from 0.12% to 7.50%. The equation between AC and GA was: median AC (cm)=GA (wk)-5. Through this formula, the absolute percentage error was analyzed same as above and it ranged from 0.30% to 4.76%. Lastly the derived formula between FL and GA was: median FL (cm)=GA (wk)/5 and the absolute percentage error ranged from 4.52% to 16.75%.
CONCLUSION
The three simple formulae suggested in our study showed a significantly easy way to estimate the median values of fetal biometry at each gestational week with good reliability.

Keyword

Biometry; Formula; Mathematical; Ultrasonography

MeSH Terms

Biometry*
Femur
Gestational Age*
Reference Values
Retrospective Studies
Ultrasonography

Figure

• 

  Fig. 1 Schematic comparison between observed, calculated and reference data in graphs. (A), (B), and (C) depict values of calculated, observed and reference values of fetal biparietal diameter (BPD), abdominal circumference (AC) and femur length (FL), respectively. The figures show that the values are quite approximate throughout all gestational weeks (after gestational age [GA] 20 weeks).

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