Accuracy of body weight estimation for fetuses with congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a serious condition characterized by the herniation of abdominal organs into the thoracic cavity, which may lead to lung hypoplasia. Over recent decades, advancements in fetal diagnostic techniques and immediate neonatal management, including the use of inhaled nitric oxide and extracorporeal membrane oxygenation (ECMO) therapy, have significantly improved the survival rates of CDH newborns. To initiate ECMO therapy promptly after birth, it is essential not only to prepare the equipment and blood products but also to provide the family with sufficient explanations prior to delivery. However, since ECMO therapy in lower birth weight (BW), newborns poses significant risks for morbidity and mortality,1 accurate estimation of fetal body weight is crucial, particularly in severe cases where ECMO therapy may be required shortly after birth. Clinically, in severe cases where the estimated fetal body weight (EFBW) is below 2500 g, the extent of ECMO preparation and prenatal family counseling largely depends on the EFBW. EFBW is calculated using ultrasound measurements of biparietal diameter (BPD), abdominal circumference (AC), and femur length (FL) with the standard formula: EFBW (g) = 1.07 × BPD (cm)3 + 0.3 × AC (cm)2 × FL (cm).2 It has been noted in CDH cases that the fetal cerebellum tends to be relatively large, leading to a fetal head circumference of approximately 0.5 standard deviations above the mean at >35 weeks gestational age.3 Additionally, severe CDH cases featuring liver herniation may exhibit a smaller AC due to the significant protrusion of abdominal organs into the thoracic cavity through the diaphragmatic defect. These anatomical variations raise concerns that EFBW calculated from observed ultrasound measurements may not accurately indicate BW in CDH cases. Although previous reports have addressed this issue,4, 5 this study specifically aimed to evaluate the accuracy of EFBW in CDH newborns with a particular focus on the severity. In this retrospective study, we examined newborns with CDH delivered at our perinatal center between January 2011 and December 2023. Parenteral informed consent was waived by the Ethics Committee of Hyogo Prefectural Kobe Children's Hospital due to the retrospective design of the study, however, parents were informed through the hospital's website and bulletin board. The Ethics Committee approved this retrospective study (R5-119). EFBW was calculated using the standard formula2 by attending obstetrician. The study analyzed the correlation between EFBW measured within 7 days before delivery and BW, stratifying the analysis into non-severe and severe cases based on the presence of liver herniation or whether the observed/expected lung area to head circumference ratio (o/e LHR) was <35 or ≥ 35.6 All analyses were performed using JMP 13 software (SAS Institute, Cary, NC). During the study period, 58 newborns with CDH were delivered at our perinatal center. After excluding 16 patients for chromosomal abnormalities (n = 7), genetic disorders (n = 4), and lack of fetal body measurements within 7 days before delivery (n = 5), 42 newborns with EFBW measurements taken within 7 days before delivery were included in this study. Perinatal characteristics, fetal body measurements, and neonatal body measurements are summarized in Table S1. A significant strong correlation was observed between EFBW and BW across all cases (R = 0.88, Figure 1A). When stratified by severity, the correlations were similar between non-severe and severe cases (Figure 1B, C). When focused on the 5 cases with BW of <2500 g, one of which received ECMO therapy, EFBW and BW were comparable, as shown in Table S2. This study represents the investigation into the correlation between EFBW and BW in CDH newborns. Despite concerns regarding potential inaccuracies in EFBW measurements due to fetal anatomical variations, the observed correlation was robust, regardless of severity. Although the HC was slightly large as previously reported,2 it is believed that the reason lies in the fact that the AC was around the average level. While further validation with a larger sample size is necessary, our preliminary findings suggest that EFBW, calculated using the standard formula, can predict BW in CDH newborns with clinically acceptable accuracy levels, even in severe cases. Accurate assessment of EFBW will be beneficial not only for determining the indication of ECMO therapy but also for planning surgical procedures after birth. We thank Drs. Shinya Tairaku and Toru Funakoshi, Department of Obstetrics and Gynecology, for their valuable assistance. The authors have no conflicts of interest to declare. Table S1. Perinatal characteristics, fetal body measurements, and neonatal body measurements in study newborns. Table S2. Characteristics of 5 congenital diaphragmatic hernia newborns with BW of <2500 g. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.