(900) A novel fetal MRI lung volume nomogram stratified by estimated fetal weight

MRI total fetal lung volumes (TLV), and observed-to-expected TLV (O/E TLV) are increasingly used to prognosticate neonatal outcomes in fetuses with suspected pulmonary hypoplasia. However, pregnancies complicated by fetal anomalies are often also complicated by FGR, and existing lung volume nomograms are stratified by gestational age (GA) rather than EFW. Therefore, if a low O/E TLV is found in a fetus with pulmonary hypoplasia and FGR, it is unclear whether the lungs are “small” because of the pathology, or small fetal size. Our aim was to develop a novel fetal lung volume nomogram stratified by EFW and GA.

Study Design:

Consecutive fetal MRIs performed at a quaternary medical center from 2019 to 2021 were analyzed. MRIs performed due to fetal lung anomalies, and cases with FGR were excluded. All MRIs were performed without IV contrast on GE 3 or 1.5 Tesla scanners. Images were reviewed by two experienced fetal radiologists. Axial Single Shot Fast Spin Echo series covering the entire fetal lungs were chosen for calculating the volumes. Freehand ROI in square mm were drawn around the contours of the lungs on consecutive slices from apex to the base. The volume of the right, left and total lungs were calculated in mL. Lung volumes were plotted by both GA and EFW.

Results:

Among 301 MRI studies performed during the study period, 178 cases met inclusion criteria. MRIs were performed between 19 to 38 weeks’ gestation (Figure 1). A sonographic EFW was obtained within 3 days (SD±5.4 days) of each MRI in all cases, with EFW ranging from 235 to 4006 gms. A GA- and an EFW-based nomogram was created using 200 gm intervals (Figure 2). A logistic regression formula using EFW to predict total lung volume was calculated: LV=0.08137803 EFW^0.86943 (R²=0.86).

Conclusion:

We developed a novel fetal lung volume nomogram stratified by EFW and GA using the same cohort. Comparison of an O/E TLV by both nomograms may assist clinicians when analyzing lung volumes in fetuses with pulmonary hypoplasia and FGR. Validation of the EFW nomogram’s predictive utility for neonatal outcomes is warranted in additional cohorts.