Reliability of sonographic fetal weight estimation in triplet pregnancies: a retrospective cohort study

Archives of Gynecology and Obstetrics https://doi.org/10.1007/s00404-018-4746-0 MATERNAL-FETAL MEDICINE Reliability of sonographic fetal weight estimation in triplet pregnancies: a retrospective cohort study Sophie Pils1 · Stephanie Springer2 · Rudolf Seemann3 · Verena Wehrmann1 · Christof Worda2 · Johannes Ott1 Received: 7 August 2017 / Accepted: 12 March 2018 © The Author(s) 2018 Abstract Purpose To review our experience in ultrasound fetal weight estimation in our large population of triplet pregnancies. Methods Ninety-seven triplet pregnancies were retrospectively included between January 2003 and January 2017. Sonographic fetal weight estimation using Hadlock’s and Schild’s formulas was compared to actual birth weight in a tertiary-care center in Vienna, Austria. Statistical analyses were performed using a stepwise linear regression model and crosstabs. Results The median discrepancy between the sonographically estimated fetal weight by Hadlock’s formula and the actual birth weight was 106 g (IQR 56–190). The percentage error and its standard deviation were − 2.5 ± 12.1%, and the median percentage error was − 3.6%. Concerning the use of Hadlock’s formula, estimated fetal weight was the most important factor predictive of actual birth weight with an estimate of 0.920 (p < 0.001). Female neonates had been overestimated by a mean of 50.473 g per fetus. The sonographic prediction of small-for-gestational-age neonates was significantly reliable (p < 0.001), with positive and negative predictive values ranging from 81.3 to 100.0%. Similar results were obtained for Schild’s formula. Conclusion Even if sonographically estimated fetal weight in triplet pregnancies has a high overall accuracy of fetal weight estimation, there are some limitations in prediction of intrauterine growth restrictions, especially in female fetuses. Keywords Fetal weight · Birth weight · Multiple pregnancy · Triplet pregnancy · Ultrasound Introduction In times of increasing number of multiple pregnancies that also include triplets [1], clinical knowledge of these issues needs to be expanded. Exact sonographic estimation of fetal weight before delivery is essential in these pregnancies for several reasons: triplet pregnancies are associated with high rates of preterm deliveries [2–5]; and the teams on the neonatal intensive care units need the information before * Johannes Ott 1 Clinical Division of Gynecologic Endocrinology and Reproductive Medicine, Department of Obstetrics and Gynecology, Medical University of Vienna, Waehringer Guertel 18‑20, 1090 Vienna, Austria 2 Clinical Division of Obstetrics and Fetomaternal Medicine, Department of Obstetrics and Gynecology, Medical University of Vienna, Waehringer Guertel 18‑20, 1090 Vienna, Austria 3 Department of Craniomaxillofacial and Oral Surgery, Medical University of Vienna, Waehringer Guertel 18‑20, 1090 Vienna, Austria delivery to be accurately prepared for postnatal treatment. Moreover, there is an increased incidence of fetal growth restriction in triplets [6], which is linked to higher risks for preterm delivery, poor perinatal outcomes, and increased mortality and morbidity [7, 8]. And, last but not least, birthweight discordance is significantly associated with fetal and neonatal mortality in both twin and triplet pregnancies [9]. Ultrasound is the only tool to predict fetal weight. Accuracy depends on clinical experience, surrounding factors including the time interval between weight estimation and delivery, and quality of the equipment [10]. Moreover, the performance of ultrasound could be seen as more difficult in triplets. Empirically, especially non-experts can experience troubles in fetal sonography due to higher risk of malpresentation and double measurements. In addition, birth-weight discordance is common among multiple pregnancies [6]. Thus, the question arises whether ultrasound is a reliable method in triplet pregnancies. Evidence about the accuracy of sonographically estimated fetal weight in triplet pregnancies is scarce [8–13]. Although good correlations between estimated fetal weight and actual birth weight have been 13 Vol.:(0123456789) Archives of Gynecology and Obstetrics reported [12], the reliability for the identification of growthrestricted fetuses seems suboptimal [8, 13]. Because only a few studies have been published that have addressed this issue directly, providing more evidence seems warranted. Thus, we aimed to present an analysis of our clinical experience with sonographic fetal weight estimation and its accuracy in our large, retrospective population of triplet pregnancies. The focus was also on factors that add to biometry’s predictive value for an accurate estimation of the actual birth weight, as well as on the reliability to predict small-for-gestational-age (SGA) neonates and growth discrepancy. Materials and methods Patient population and study design In this retrospective analysis, we studied 135 women who were diagnosed with a triplet pregnancy at the time of the first trimester screening from January 2003 to January 2017. The following patients were then excluded from the study: seven women did not deliver at the department and had no follow-up and there were missing data in ten women. Moreover, we excluded all women who underwent multifetal pregnancy reduction (n = 15) or had an intrauterine fetal death (IUFD) of at least one fetus before the onset of viability (n = 6). This means that, only cases that started with triplets and gave birth to triplets were included. This resulted in a final study population of 97 triplet pregnancies with 291 fetuses/neonates for this analysis. Parts of these data have been published previously with a focus on serial cervical length measurements [14]. As reported previously [14–16], a screening program for pregnant women at perceived risk of preterm delivery, which includes multiple pregnancies, has been established for many years at the Department of Maternal–Fetal Medicine of the Medical University of Vienna, Austria. The department is the reference center for maternal–fetal medicine in Eastern Austria and the annual number of deliveries was at least 2500 during the study period. The screening program included fetal biometry using Hadlock’s formula [17] and cervical length measurement by transvaginal ultrasound every 2 weeks from week 16 + 0 until delivery. All ultrasound examinations were performed by highly experienced obstetricians, all members of the clinical working group for multiple pregnancies, and were performed on the same two ultrasound devices. A Toshiba Power Vision (Toshiba, Tokyo, Japan) ultrasound machine was used until 2010, and a Toshiba Aplio MX (Toshiba, Tokyo, Japan) machine since 2010. The basic perinatology database at the department uses the Viewpoint® software (GE Healthcare, Wessling, 13 Germany), which was also used for data acquisition. In a retrospective data set, it can be considerably difficult to correlate each fetu (...truncated)