Ultrasonographic Fetal Weight Estimation: Should Macrosomia-Specific Formulas Be Utilized?

Area of Science:

• Obstetrics and Gynecology
• Fetal Medicine
• Maternal-Fetal Medicine

Background:

• Accurate estimation of fetal weight (EFW) is crucial for managing pregnancies, particularly those with suspected fetal macrosomia.
• Existing formulas, like Hadlock IV, may have limitations in accurately estimating the weight of macrosomic fetuses (birth weight ≥ 4 kg).

Purpose of the Study:

• To derive and validate a new EFW formula specifically for macrosomic fetuses.
• To compare the accuracy of the new macrosomic formula against the Hadlock IV formula.
• To determine if incorporating maternal diabetes mellitus (MDM) status improves EFW estimation in macrosomic fetuses.

Main Methods:

• Retrospective review of 403 nonanomalous singleton pregnancies with birth weight ≥ 4 kg and biometric data within 14 days of birth.
• Development of a macrosomic-specific EFW formula using multivariable linear regression on a training dataset.
• Validation of the formula using a separate validation dataset and comparison of accuracy metrics (ME, AME, MPE) with the Hadlock IV formula.
• Development and evaluation of diabetes-specific formulas to assess their impact on accuracy.

Main Results:

• The derived macrosomic formula demonstrated significantly lower mean error (ME), absolute mean error (AME), and mean percent error (MPE) compared to the Hadlock IV formula in both training and validation datasets.
• The Hadlock IV formula systematically underestimated fetal birth weight in this cohort.
• EFW formulas specifically for maternal diabetes did not show improved accuracy compared to the general macrosomic formula.

Conclusions:

• A dedicated EFW formula for macrosomic fetuses significantly outperforms the Hadlock IV formula, which tends to underestimate fetal weight.
• Maternal diabetes status does not enhance the accuracy of EFW estimation in macrosomic fetuses when using specific formulas.
• Clinicians should consider using a macrosomic-specific EFW formula when fetal macrosomia is suspected to improve weight estimation accuracy.