Prenatal sonographic assessment of fetal weight
- Andrew P MacKenzie, MD
Andrew P MacKenzie, MD
- Assistant Professor of Obstetrics and Gynecology
- University of Connecticut
- Director of Maternal Fetal Medicine
- St Francis Hospital and Medical Center
- Courtney D Stephenson, DO
Courtney D Stephenson, DO
- Director, Charlotte Fetal Care Center
- Associate Director of Maternal-Fetal Medicine
- Carolinas Medical Center
- Clinical Professor, University of North Carolina
- Edmund F Funai, MD
Edmund F Funai, MD
- Professor and Chief Operating Officer
- USF Health
Monitoring fetal growth is a standard component of antenatal care. Investigators have developed several equations for estimating fetal weight in the late second and the third trimester. These equations involve a variety of sonographically obtained biometric measurements. The fetal weight derived from these equations is then compared to distributions normalized for gestational age to identify growth outside the norm. Since abnormalities of fetal growth are associated with an increased risk of adverse outcome, this information often affects how the pregnancy and delivery will be managed.
Techniques for obtaining biometric measurements used in assessment of gestational age and fetal weight can be found separately. (See "Prenatal assessment of gestational age and estimated date of delivery".)
Ultrasound examination typically involves measurement of multiple biometric parameters that are incorporated into a formula for calculating estimated fetal weight (EFW). Most commonly, a combination of biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL) is used. The two most popular formulas are Warsof's  with Shepard's modification  and Hadlock's [3,4]. These formulas are included in most ultrasound equipment packages. However, at least 30 formulas for estimating fetal weight have been published.
Performance — A well-designed prospective study compared estimated and actual birth weight in 441 pregnancies delivered within 48 hours of ultrasonography . Twenty-nine different formulas were used to calculate EFW. All of the pregnancies were singletons and 99 percent of the mothers were Caucasian. For birthweights between 3.0 and 3.5 kg, 80 percent of EFWs were within 10 percent of birthweight. Formulas using head, abdomen, and femur measurements resulted in the lowest mean absolute percentage error (about 8 percent). A retrospective cohort study of the accuracy of estimated fetal weight within one week of delivery using 23 fetal weight estimation models concluded the Sabbagha formula , which like Hadlock uses head, abdomen, and femur measurements but also incorporates gestational age, resulted in the lowest mean percentage error (-1.5 to 3.3 percent) .
A systematic review of studies that compared ultrasound estimated fetal weight (EFW) with birth weight included 11 different methods of fetal weight assessment . These studies consistently observed that in 5 percent of fetuses, the random error in fetal weight estimation exceeded 14 percent of birth weight. Both intraobserver and interobserver variability was large. The authors concluded that volumetric methods had some advantages, but there was no consistently superior method of sonographic determination of fetal weight.
Subscribers log in hereLiterature review current through: Jun 2017. | This topic last updated: Oct 06, 2016.References
- Warsof SL, Gohari P, Berkowitz RL, Hobbins JC. The estimation of fetal weight by computer-assisted analysis. Am J Obstet Gynecol 1977; 128:881.
- Shepard MJ, Richards VA, Berkowitz RL, et al. An evaluation of two equations for predicting fetal weight by ultrasound. Am J Obstet Gynecol 1982; 142:47.
- Hadlock FP, Harrist RB, Fearneyhough TC, et al. Use of femur length/abdominal circumference ratio in detecting the macrosomic fetus. Radiology 1985; 154:503.
- Hadlock FP, Harrist RB, Sharman RS, et al. Estimation of fetal weight with the use of head, body, and femur measurements--a prospective study. Am J Obstet Gynecol 1985; 151:333.
- Scioscia M, Vimercati A, Ceci O, et al. Estimation of birth weight by two-dimensional ultrasonography: a critical appraisal of its accuracy. Obstet Gynecol 2008; 111:57.
- Sabbagha RE, Minogue J, Tamura RK, Hungerford SA. Estimation of birth weight by use of ultrasonographic formulas targeted to large-, appropriate-, and small-for-gestational-age fetuses. Am J Obstet Gynecol 1989; 160:854.
- Barel O, Vaknin Z, Tovbin J, et al. Assessment of the accuracy of multiple sonographic fetal weight estimation formulas: a 10-year experience from a single center. J Ultrasound Med 2013; 32:815.
- Dudley NJ. A systematic review of the ultrasound estimation of fetal weight. Ultrasound Obstet Gynecol 2005; 25:80.
- Buck Louis GM, Grewal J, Albert PS, et al. Racial/ethnic standards for fetal growth: the NICHD Fetal Growth Studies. Am J Obstet Gynecol 2015; 213:449.e1.
- Siemer J, Egger N, Hart N, et al. Fetal weight estimation by ultrasound: comparison of 11 different formulae and examiners with differing skill levels. Ultraschall Med 2008; 29:159.
- Kurmanavicius J, Burkhardt T, Wisser J, Huch R. Ultrasonographic fetal weight estimation: accuracy of formulas and accuracy of examiners by birth weight from 500 to 5000 g. J Perinat Med 2004; 32:155.
- Siemer J, Hilbert A, Wolf T, et al. Gender-specific weight estimation of fetuses between 2,501 and 3,999 g--new regression formulae. Fetal Diagn Ther 2008; 24:304.
- Melamed N, Yogev Y, Ben-Haroush A, et al. Does use of a sex-specific model improve the accuracy of sonographic weight estimation? Ultrasound Obstet Gynecol 2012; 39:549.
- Schild RL, Fimmers R, Hansmann M. Fetal weight estimation by three-dimensional ultrasound. Ultrasound Obstet Gynecol 2000; 16:445.
- Tuuli MG, Kapalka K, Macones GA, Cahill AG. Three-Versus Two-Dimensional Sonographic Biometry for Predicting Birth Weight and Macrosomia in Diabetic Pregnancies. J Ultrasound Med 2016; 35:1925.
- Aksoy H, Aksoy Ü, Karadağ Öİ, et al. Influence of maternal body mass index on sonographic fetal weight estimation prior to scheduled delivery. J Obstet Gynaecol Res 2015; 41:1556.
- Khalil A, D'Antonio F, Dias T, et al. Ultrasound estimation of birth weight in twin pregnancy: comparison of biometry algorithms in the STORK multiple pregnancy cohort. Ultrasound Obstet Gynecol 2014; 44:210.
- Diaz-Garcia C, Bernard JP, Ville Y, Salomon LJ. Validity of sonographic prediction of fetal weight and weight discordance in twin pregnancies. Prenat Diagn 2010; 30:361.
- Danon D, Melamed N, Bardin R, Meizner I. Accuracy of ultrasonographic fetal weight estimation in twin pregnancies. Obstet Gynecol 2008; 112:759.
- Papageorghiou AT, Ohuma EO, Altman DG, et al. International standards for fetal growth based on serial ultrasound measurements: the Fetal Growth Longitudinal Study of the INTERGROWTH-21st Project. Lancet 2014; 384:869.
- Villar J, Cheikh Ismail L, Victora CG, et al. International standards for newborn weight, length, and head circumference by gestational age and sex: the Newborn Cross-Sectional Study of the INTERGROWTH-21st Project. Lancet 2014; 384:857.
- Kehl S, Schmidt U, Spaich S, et al. What are the limits of accuracy in fetal weight estimation with conventional biometry in two-dimensional ultrasound? A novel postpartum study. Ultrasound Obstet Gynecol 2012; 39:543.