Effect of Maternal Body Mass Index and Amniotic Fluid Index on the Accuracy of Sonographic Estimation of Fetal Weight in Late Gestation

Abstract

Objective The objective of this study was to determine the effect, if any, of maternal body mass index (BMI) and amniotic fluid index (AFI) on the accuracy of sonographic estimated fetal weight (EFW) at 40 to 42 weeks' gestation.

Methods This was a retrospective cohort study of singleton gestations with ultrasound performed at 40 to 42 weeks from 2010 to 2013. In this study, patients with documented BMI and sonographic EFW and AFI, concurrently, within 7 days of delivery were included. Chronic medical conditions and fetal anomalies were excluded from this study. The primary variable of interest was the rate of substantial error in EFW, defined as absolute percentage error (APE) >10%.

Results A total of 1,000 pregnancies were included. Overall, the APE was 6.0 ± 4.5% and the rate of substantial error was 17.4% (n = 174). There was no significant difference in APE or rate of substantial error between BMI groups. In the final multivariable logistic regression model, the rate of substantial error was increased in women with oligohydramnios (OR 1.79; 95% CI: 1.10–2.92). Furthermore, oligohydramnios was significantly more likely to overestimate EFW while polyhydramnios was more likely to underestimate EFW. Maternal BMI did not affect the accuracy of sonographic EFW.

Conclusion Sonographic EFW may be affected by extremes of AFI in the postdates period. Maternal BMI does not affect EFW accuracy at 40 to 42 weeks.

Keywords

estimated fetal weight - amniotic fluid index - oligohydramnios - polyhydramnios - obesity - body mass index

Note

The results of this study were presented at the Society for Maternal-Fetal Medicine 37th Annual Scientific Meeting in Las Vegas, Nevada in January 2017.

• References

• 1 Dudley NJ. A systematic review of the ultrasound estimation of fetal weight. Ultrasound Obstet Gynecol 2005; 25 (01) 80-89
• 2 Kritzer S, Magner K, Warshak CR. Increasing maternal body mass index and the accuracy of sonographic estimation of fetal weight near delivery. J Ultrasound Med 2014; 33 (12) 2173-2179
• 3 Field NT, Piper JM, Langer O. The effect of maternal obesity on the accuracy of fetal weight estimation. Obstet Gynecol 1995; 86 (01) 102-107
• 4 Blann DW, Prien SD. Estimation of fetal weight before and after amniotomy in the laboring gravid woman. Am J Obstet Gynecol 2000; 182 (05) 1117-1120
• 5 Farrell T, Holmes R, Stone P. The effect of body mass index on three methods of fetal weight estimation. BJOG 2002; 109 (06) 651-657
• 6 Barnhard Y, Bar-Hava I, Divon MY. Accuracy of intrapartum estimates of fetal weight. Effect of oligohydramnios. J Reprod Med 1996; 41 (12) 907-910
• 7 Benacerraf BR, Gelman R, Frigoletto Jr FD. Sonographically estimated fetal weights: accuracy and limitation. Am J Obstet Gynecol 1988; 159 (05) 1118-1121
• 8 Heer IM, Kumper C, Vogtle N, Muller-Egloff S, Dugas M, Strauss A. Analysis of factors influencing the ultrasonic fetal weight estimation. Fetal Diagn Ther 2008; 23 (03) 204-210
• 9 Ashwal E, Hiersch L, Melamed N, Bardin R, Wiznitzer A, Yogev Y. Does the level of amniotic fluid have an effect on the accuracy of sonographic estimated fetal weight at term?. J Matern Fetal Neonatal Med 2015; 28 (06) 638-642
• 10 Barel O, Maymon R, Vaknin Z, Tovbin J, Smorgick N. Sonographic fetal weight estimation - is there more to it than just fetal measurements?. Prenat Diagn 2014; 34 (01) 50-55
• 11 Hadlock FP, Harrist RB, Sharman RS, Deter RL, Park SK. Estimation of fetal weight with the use of head, body, and femur measurements—a prospective study. Am J Obstet Gynecol 1985; 151 (03) 333-337
• 12 Goetzinger KR, Odibo AO, Shanks AL, Roehl KA, Cahill AG. Clinical accuracy of estimated fetal weight in term pregnancies in a teaching hospital. J Matern Fetal Neonatal Med 2014; 27 (01) 89-93
• 13 Kehl S, Schmidt U, Spaich S, Schild RL, Sütterlin M, Siemer J. 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 (05) 543-548
• 14 Obesity: preventing and managing the global epidemic. Report of a WHO consultation. World Health Organ Tech Rep Ser 2000; 894: i-xii , 1–253
• 15 Scioscia M, Vimercati A, Ceci O, Vicino M, Selvaggi LE. Estimation of birth weight by two-dimensional ultrasonography: a critical appraisal of its accuracy. Obstet Gynecol 2008; 111 (01) 57-65
• 16 Ott WJ, Doyle S, Flamm S. Accurate ultrasonic estimation of fetal weight. Am J Perinatol 1985; 2 (03) 178-182
• 17 Melamed N, Yogev Y, Ben-Haroush A, Meizner I, Mashiach R, Glezerman M. Does use of a sex-specific model improve the accuracy of sonographic weight estimation?. Ultrasound Obstet Gynecol 2012; 39 (05) 549-557