A simple estimated fetal weight equation based on real-time ultrasound measurements of fetuses less than thirty-four weeks' gestation

Gary R. Thurnau*, Ralph K. Tamura, Rudy Sabbagha, O. Richard Depp, Alan Dyer, Ron Larkin, Timothy Lee, Colby Laughlin

*Corresponding author for this work

Research output: Contribution to journalArticle

66 Scopus citations


Based on ultrasonographic mensuration, a number of equations have previously been devised for the purpose of estimating fetal weights. The objective of this study was to develop a mathematical equation that is simple, accurate, and easy to use when applied to preterm or low-birth weight fetuses (<2,500 gm). Real-time ultrasound measurements of fetal biparietal diameters (BPDs) and abdominal circumferences (ACs) were obtained in 62 pregnant women within one week of premature delivery. Mean gestational age and mean birth weight ± SD for this study group of neonates were 28.5 ± 3.5 weeks and 1,135 ± 343 gm, respectively. With the aid of computer analysis, a simple regression equation was derived: EFW = (BPD x AC x 9.337) -299. When predicted estimated fetal weight (EFW) was compared with actual birth weight (ABW), multiple regression analysis demonstrated a correlation coefficient (R) of 0.957. Preliminary results on 19 oatients of a prospective study showed an absolute mean difference between the computed EFWs and the ABWs to be within 7.0% of ABW (70 gm/kg of ABW). The standard deviation of the difference was 9.3% of ABW (93 gm/kg of ABW). Based on these data, this simple equation appears to be clinically reliable and easy to use when estimating weights of preterm or low-birth weight fetuses of less than 2,500 gm.

Original languageEnglish (US)
Pages (from-to)557-561
Number of pages5
JournalAmerican journal of obstetrics and gynecology
Issue number5
StatePublished - Mar 1 1983


ASJC Scopus subject areas

  • Obstetrics and Gynecology

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