Estimation of Fetal Weight during Labor: Still a Challenge

Abstract

Objective To evaluate the accuracy of fetal weight prediction by ultrasonography labor employing a formula including the linear measurements of femur length (FL) and mid-thigh soft-tissue thickness (STT).

Methods We conducted a prospective study involving singleton uncomplicated term pregnancies within 48 hours of delivery. Only pregnancies with a cephalic fetus admitted in the labor ward for elective cesarean section, induction of labor or spontaneous labor were included. We excluded all non-Caucasian women, the ones previously diagnosed with gestational diabetes and the ones with evidence of ruptured membranes. Fetal weight estimates were calculated using a previously proposed formula [estimated fetal weight = − 1687.47 + (54.1 × FL) + (76.68 × STT). The relationship between actual birth weight and estimated fetal weight was analyzed using Pearson's correlation. The formula's performance was assessed by calculating the signed and absolute errors. Mean weight difference and signed percentage error were calculated for birth weight divided into three subgroups: < 3000 g; 3000–4000g; and > 4000 g.

Results We included for analysis 145 cases and found a significant, yet low, linear relationship between birth weight and estimated fetal weight (p < 0.001; R² = 0.197) with an absolute mean error of 10.6%. The lowest mean percentage error (0.3%) corresponded to the subgroup with birth weight between 3000 g and 4000 g.

Conclusions This study demonstrates a poor correlation between actual birth weight and the estimated fetal weight using a formula based on femur length and mid-thigh soft-tissue thickness, both linear parameters. Although avoidance of circumferential ultrasound measurements might prove to be beneficial, it is still yet to be found a fetal estimation formula that can be both accurate and simple to perform.

Resumo

Objetivo Avaliar a precisão da determinação ultrassonográfica da estimativa de peso fetal recorrendo apenas a parâmetros lineares (comprimento do fémur – FL - e espessura de tecido mole a meio da coxa fetal - STT), no período precedente ao parto.

Métodos Realizamos um estudo prospectivo que incluiu gestações simples de termo, com feto cefálico, nas quais o parto ocorreu nas 48h seguintes à avaliação ecográfica. A inclusão no estudo foi feita no momento de admissão ao bloco de partos para cesariana eletiva, indução do trabalho de parto ou trabalho de parto espontâneo. Foram excluídas todas as grávidas não caucasianas, com diagnóstico de diabetes gestacional ou evidência de rotura de membranas. A estimativa de peso fetal foi calculada através de uma fórmula previamente publicada [estimativa de peso fetal = − 1687,47 + (54,1 × FL) + (76,68 × STT). A relação entre o peso real e o peso estimado foi analisada através da correlação de Pearson. O desempenho desta fórmula foi avaliado através do cálculo da percentagem de erro absoluto e não absoluto. Os recém-nascidos foram divididos em 3 grupos consoante o peso real: < 3000 g; 3000 g – 4000 g; e > 4000 g; para cada grupo foi calculada diferença média entre a estimativa de peso e o peso real e a percentagem de erro associada.

Resultados Incluímos 145 casos no estudo, cuja estimativa de peso e peso real se correlacionaram significativamente, apesar do valor de correlação ser pouco elevado (p < 0,001; R² = 0,197). Globalmente, a percentagem de erro absoluto foi 10,6%. A percentagem de erro mais baixa correspondeu ao grupo com peso real entre 3000 g e 4000 g.

Conclusões Com este estudo demonstramos uma correlação fraca entre o peso real e a estimativa de peso fetal ultrassonográfica, quando calculada com base numa fórmula que usa o comprimento do fémur e a espessura de tecido mole a meio da coxa fetal, ambos parâmetros lineares. Ainda que a exclusão de parâmetros circunferenciais no cálculo da estimativa de peso fetal se venha a provar benéfica, esta não parece ser uma fórmula simultaneamente simples e precisa no cálculo da estimativa de peso fetal.

Keywords

estimation fetal weight - labor - macrossomia - low birth weight

Palavras-chave

estimativa de peso fetal - parto - macrossomia - recém-nascido de baixo peso

• References

• 1 Najafian M, Cheraghi M. Occurrence of fetal macrosomia rate and its maternal and neonatal complications: a 5-year cohort study. ISRN Obstet Gynecol 2012; 2012: 353791
• 2 Weissmann-Brenner A, Simchen MJ, Zilberberg E , et al. Maternal and neonatal outcomes of macrosomic pregnancies. Med Sci Monit 2012; 18 (9) PH77-PH81
• 3 Bamberg C, Hinkson L, Henrich W. Prenatal detection and consequences of fetal macrosomia. Fetal Diagn Ther 2013; 33 (3) 143-148
• 4 Valero De Bernabé J, Soriano T, Albaladejo R , et al. Risk factors for low birth weight: a review. Eur J Obstet Gynecol Reprod Biol 2004; 116 (1) 3-15
• 5 Lindqvist PG, Molin J. Does antenatal identification of small-for-gestational age fetuses significantly improve their outcome?. Ultrasound Obstet Gynecol 2005; 25 (3) 258-264
• 6 Walsh JM, McAuliffe FM. Prediction and prevention of the macrosomic fetus. Eur J Obstet Gynecol Reprod Biol 2012; 162 (2) 125-130
• 7 Dudley NJ. A systematic review of the ultrasound estimation of fetal weight. Ultrasound Obstet Gynecol 2005; 25 (1) 80-89
• 8 Faschingbauer F, Dammer U, Raabe E , et al. Sonographic weight estimation in fetal macrosomia: influence of the time interval between estimation and delivery. Arch Gynecol Obstet 2015; 292 (1) 59-67
• 9 Lalys L, Pineau JC, Guihard-Costa AM. Small and large foetuses: Identification and estimation of foetal weight at delivery from third-trimester ultrasound data. Early Hum Dev 2010; 86 (12) 753-757
• 10 Pressman EK, Bienstock JL, Blakemore KJ, Martin SA, Callan NA. Prediction of birth weight by ultrasound in the third trimester. Obstet Gynecol 2000; 95 (4) 502-506
• 11 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 (2) 155-161
• 12 Shamley KT, Landon MB. Accuracy and modifying factors for ultrasonographic determination of fetal weight at term. Obstet Gynecol 1994; 84 (6) 926-930
• 13 Yarkoni S, Reece EA, Wan M, Holford T, Romero R, Hobbins JC. Intrapartum fetal weight estimation: a comparison of three formulae. J Ultrasound Med 1986; 5 (12) 707-710
• 14 Chang TC, Robson SC, Spencer JA, Gallivan S. Ultrasonic fetal weight estimation: analysis of inter- and intra-observer variability. J Clin Ultrasound 1993; 21 (8) 515-519
• 15 Scioscia M, Scioscia F, Vimercati A , et al. Estimation of fetal weight by measurement of fetal thigh soft-tissue thickness in the late third trimester. Ultrasound Obstet Gynecol 2008; 31 (3) 314-320
• 16 Yang F, Leung KY, Hou YW, Yuan Y, Tang MH. Birth-weight prediction using three-dimensional sonographic fractional thigh volume at term in a Chinese population. Ultrasound Obstet Gynecol 2011; 38 (4) 425-433
• 17 Abuelghar W, Khairy A, El Bishry G, Ellaithy M, Abd-Elhamid T. Fetal mid-thigh soft-tissue thickness: a novel method for fetal weight estimation. Arch Gynecol Obstet 2014; 290 (6) 1101-1108
• 18 Scioscia M, Stepniewska A, Trivella G, De Mitri P, Bettocchi S. Estimation of birthweight by measurement of fetal thigh soft-tissue thickness improves the detection of macrosomic fetuses. Acta Obstet Gynecol Scand 2014; 93 (12) 1325-1328
• 19 Larciprete G, Di Pierro G, Barbati G , et al. Could birthweight prediction models be improved by adding fetal subcutaneous tissue thickness?. J Obstet Gynaecol Res 2008; 34 (1) 18-26
• 20 O'Connor C, Farah N, O'Higgins A , et al. Longitudinal measurement of fetal thigh soft tissue parameters and its role in the prediction of birth weight. Prenat Diagn 2013; 33 (10) 945-951
• 21 Kalantari M, Negahdari A, Roknsharifi S, Qorbani M. A new formula for estimating fetal weight: The impression of biparietal diameter, abdominal circumference, mid-thigh soft tissue thickness and femoral length on birth weight. Iran J Reprod Med 2013; 11 (11) 933-938
• 22 Frates MC. Mistakes to avoid in the second and third trimesters: fetal measurements and anatomy. Ultrasound Clin 2012; 7 (1) 15-31
• 23 Farah N, Stuart B, Donnelly V, Rafferty G, Turner M. What is the value of ultrasound soft tissue measurements in the prediction of abnormal fetal growth?. J Obstet Gynaecol 2009; 29 (6) 457-463
• 24 Melamed N, Yogev Y, Meizner I, Mashiach R, Bardin R, Ben-Haroush A. Sonographic fetal weight estimation: which model should be used?. J Ultrasound Med 2009; 28 (5) 617-629
• 25 Predanic M, Cho A, Ingrid F, Pellettieri J. Ultrasonographic estimation of fetal weight: acquiring accuracy in residency. J Ultrasound Med 2002; 21 (5) 495-500
• 26 Barel O, Vaknin Z, Tovbin J, Herman A, Maymon R. Assessment of the accuracy of multiple sonographic fetal weight estimation formulas: a 10-year experience from a single center. J Ultrasound Med 2013; 32 (5) 815-823
• 27 Porter B, Neely C, Szychowski J, Owen J. Ultrasonographic fetal weight estimation: should macrosomia-specific formulas be utilized?. Am J Perinatol 2015; 32 (10) 968-972
• 28 Noumi G, Collado-Khoury F, Bombard A, Julliard K, Weiner Z. Clinical and sonographic estimation of fetal weight performed during labor by residents. Am J Obstet Gynecol 2005; 192 (5) 1407-1409
• 29 Dimassi K, Douik F, Ajroudi M, Triki A, Gara MF. Ultrasound fetal weight estimation: how accurate are we now under emergency conditions?. Ultrasound Med Biol 2015; 41 (10) 2562-2566