Prenatal estimation of the birth weight above 4,000 g (fetal macrosomia) using fetal abdominal circumference(AC)

Abstract

Purpose: This study is to determine if the birth weight above 4,000g can be correctly estimated by prenatal ultrasonographic measurements of abdominal circumference.

Background: The delivery of macrosomatic fetus can increase the perinatal morbidity and mortality of both parturients and fetuses/neonates; the risk for shoulder dystocia, fetal asphyxia and birth trauma as well as vacuum or forceps delivery, hysterotomy and postpartum bleeding due to uterine atony. Thus, the accurate estimation of the birth weight is very important to do the appropriate obstetric management for the fetus and the mother. However, the prenatal weight can’t be measured directly, so it should be calculated using the formula with the fetal development indices measured by the ultrasonography. The point of importance is what kind of parameters would make the most correct estimation.

Materials and methods: We retrospectively studied 950 pregnant women (including primipara and multipara) who had ultrasonographic measurements for fetal development indices within 7 days before delivery and calculated for estimated birth weight. Multiple regression analysis was done using the indices of BPD, FL and AC measured by ultrasonography as independent variables and birth weight as a dependent variable; linear regression analysis between AC and birth weight was done; the regressive function was obtained and its significance was evaluated. Then we determined the AC value to predict the fetal macrosomia (estimated birth weight above 4,000g).

Results: In the group with the birth weight above 4,000g, linear regressive function between AC and birth weight was BW=361.48*AC-8663.93; thus it showed significant relation(P<0.001). AC value greater than 35 centimeters can be used to estimate the birth weights above 4,000g.