New formula for estimating fetal weight below 1000 g: comparison with existing formulas

Area of Science:

• Perinatology
• Medical Imaging
• Biostatistics

Background:

• Accurate estimation of fetal weight (EFW) is vital for perinatal care, particularly for fetuses at the limit of viability.
• Existing EFW formulas are often derived from larger fetal populations, potentially limiting their accuracy in predicting birth weight for very small fetuses (<1000 g).

Purpose of the Study:

• To develop and validate a novel ultrasonographic formula for EFW in fetuses weighing less than 1000 grams.
• To compare the accuracy of the new formula against 10 existing EFW formulas in this specific fetal weight range.

Main Methods:

• Utilized complete data from 142 pregnancies with delivery within 7 days of ultrasonographic examination.
• Developed a new formula using natural logarithm transformations of head circumference (HC), abdominal circumference (AC), and femur length (FL).
• Validated the new formula prospectively on a cohort of 27 fetuses with EFW less than 1000 g and compared its performance against 10 established formulas.

Main Results:

• The newly developed formula (In [BW] = 0.66 x 1n [HC] + 1.04 x 1n [AC] + 0.985 x 1n [FL]) showed significantly higher accuracy than all 10 existing formulas.
• The new formula also demonstrated superior performance in the prospective validation cohort.
• Among existing formulas, the Hadlock formula was the most accurate, though still significantly less accurate than the new formula.

Conclusions:

• A novel ultrasonographic formula provides significantly more accurate EFW estimations for fetuses less than 1000 grams.
• This improved accuracy is critical for clinical management of pregnancies involving fetuses at the limit of viability.
• The developed formula offers a valuable tool for enhancing perinatal care and improving outcomes for high-risk neonates.