Do specific weight formulas for fetuses < or = 1500 g really improve weight estimation?

PURPOSE

In addition to gestational age, fetal weight is an important predictive parameter for neonatal morbidity and mortality in very small fetuses. In order to improve weight estimation, specific weight formulas for fetuses under 1500 g have been introduced by several authors. The aim of the present study was therefore to compare specific weight equations for fetuses under 1500 g with widely used methods that were designed for the whole fetal weight range.

MATERIALS AND METHODS

459 pregnancies were included in order to evaluate six widely used formulas and four formulas specifically designed for very small fetuses. The inclusion criteria were a singleton pregnancy, birth weight equal to or less than 1500 g, ultrasound examination with complete biometric parameters during the 7 days prior to delivery, and an absence of structural or chromosomal malformations.

RESULTS

All formulas, except the Hadlock equations, demonstrated a significant systematic error. Regarding the random error, it was similar for most of the methods. The Scott formula showed the narrowest limits of agreement. At a discrepancy level of 5 % and 10 % between estimated fetal weight and actual birth weight, one of the Hadlock formulas included the most cases.

CONCLUSION

Weight formulas, specifically designed for very small fetuses, do not improve sonographic weight estimation substantially. Among these formulas, the Scott equation was the most accurate one. However compared to the widely used Hadlock formulas, it was not favorable.