FETAL MASS DETERMINATION

Fetal growth failure = fetal mass (weight) that is below the lower limit of normal (for the particular population being studied).

The only diagnostic factors that truly reflect fetal mass are:

• Abdominal circumference (measures liver and spleen size and subcutaneous fat accumulation).
• Head circumference (measure brain size).

FORMULAS FOR DETERMINING FETAL WEIGHT

Formulas For Determining Fetal Weight

ERRORS IN ESTIMATING FETAL WEIGHT

Variable	Estimated Error ± 2 SD
AC HC/AC AC/FL HC/AC/FL FL/AC/BPD (2) BPD/AC (2) Composite fetal volume Neonatal measurement (direct) Variation by neonatal density	27% 18-25% 16% 15-17% 9.58% 11.86% 8-10% 8-10% 8-21%

REFERENCES

1. Manning F. Fetal Medicine: Principles and Practice. Appleton and Lange, Connecticut 1995:346.
2. Fleming A, Riva JD, McAdoo G. Estimation of fetal weight by ultrasound in term pregnancy. JDMS 1996;12:7-10