Effect of fetal presentation on sonographic estimation of fetal weight according to different formulas

To compare the accuracy of various sonographic estimation of fetal weight (sEFW) formulas for breech-presenting fetuses.

A retrospective analysis of sEFW performed within 3 days of delivery in a tertiary medical center in Israel between July 2007 and December 2014 was conducted. Breech-presenting singleton fetuses were matched by sex and birth weight to vertex-presenting fetuses. sEFW was calculated using 21 formulas. Systematic and random errors, proportion of estimates (POE) within 10% of actual birth weight, and reliability analysis were used to compare sonographic accuracy. The best performing formula was determined by Euclidean distance.

Both groups contained 274 fetuses. Systematic error was lower for breech fetuses when compared with control fetuses in 17 of 21 formulas; there was no significant difference in random error between the breech and vertex groups. For vertex fetuses, Euclidean distance was smaller in 17 of 21 formulas, and POE within 10% of birth weight was higher in most formulas. Cronbach α value was higher for vertex fetuses than for breech fetuses in all formulas. The formulas of Combs et al. and Hadlock et al. were highest ranking for breech-presenting fetuses.

sEFW might be more accurate for vertex than for breech fetuses.