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The accuracy of ultrasonographic fetal weight estimation in twin pregnancies is somewhat less than that achieved in singleton pregnancies, according to Israeli researchers.

The accurate estimation of fetal weight in twin gestations is very important for proper management of pregnancy and selection of the optimal mode and timing of delivery, Dr. David Danon of Beilinson Hospital, Petah Tiqva and colleagues note.

To investigate how precise the ultrasonographic approach to weight estimation might be, the team studied data for 278 twin and 834 singleton pregnancies. Measurements were made up to three days before delivery, the researchers report in the October issue of Obstetrics and Gynecology.

For the twins, the mean absolute error was 8.9 per cent compared with 6.8 per cent for singletons, a significant difference. For the first twin, the proportion was 7.5 per cent, but less accurate for the second twin, at 10.5 per cent.

In examining data on fetuses with growth restriction, the overall accuracy was also higher in the singleton group (95 per cent) than in twins (88 per cent). The investigators point out that this was mainly due to the difference in accuracy for the first and the second twin (90.6 versus 85.6 per cent).

The researchers note that the accuracy of estimates for singletons was in line with those found in other studies although the mean percentage error in twin pregnancies was higher.

This study "highlights the advantages and limitations of ultrasonography for the estimation of fetal weight," the team concludes.

Obstet Gynecol 2008;112:759-764