Ultrasound weight estimation of large fetuses.

OBJECTIVE

To compare the accuracy of fetal weight estimation in large fetuses using four ultrasound formulae.

DESIGN

Prospective comparative study.

SETTING

University Hospital, Lund, Sweden.

POPULATION

Large-for-gestational age fetuses (n= 114) at a routine ultrasound examination in the third trimester.

METHODS

The Persson & Weldner two-dimensional formula was compared with the Hart et al. two-dimensional formula incorporating maternal weight and with the Lee et al. and Lindell & Maršál three-dimensional formulae. The formulae are based on two-dimensional measurements of fetal head, abdomen and femur, and three-dimensional volumetry of fetal abdomen and thigh.

MAIN OUTCOME MEASURES

Accuracy in detection of fetuses with birthweight >4000 and >4500 g.

RESULTS

For fetuses >4000 g, the Lindell & Maršál three-dimensional formula showed significantly smaller mean absolute percentage error than the Persson & Weldner two-dimensional and the Lee et al. three-dimensional formulae (p= 0.04 and p < 0.001, respectively). No significant difference between the Lindell & Maršál three-dimensional and the Hart et al. two-dimensional formulae was found. A receiver operating characteristic curve showed a higher detection rate for fetuses with birthweight >4500 g using a three-dimensional compared with a two-dimensional technique. The best performance in detecting fetuses with birthweight >4500 g was given by the Lindell & Maršál three-dimensional formula; for estimated fetal weight >4300 g, the detection rate was 93% and false-positive rate 38%.

CONCLUSIONS

The ability to detect macrosomic fetuses in a preselected high-risk group was higher using fetal weight estimation with a three-dimensional compared with a two-dimensional ultrasound technique, with or without the inclusion of maternal weight.