Assessment of fetal lung maturity and prediction of neonatal respiratory distress syndrome by MV-Flow imaging.

PURPOSE: Neonatal respiratory distress syndrome (NRDS) is a leading cause of morbidity in preterm infants. Existing prenatal tests for fetal lung maturity are either invasive or insufficiently reliable. Microvascular flow imaging (MV-Flow) is a novel Doppler ultrasound technique capable of detecting low-velocity microvascular flow. This study evaluated its utility for visualizing fetal pulmonary microcirculation and predicting NRDS risk. METHODS: A prospective, two-part study was conducted. In part 1, 167 normal singleton pregnancies (12-42 weeks) underwent MV-Flow imaging of the fetal lungs. The vascular intensity of microvascular volume (VIMV) was measured using different regions of interest and compared with conventional Doppler; reproducibility and gestational-age trends were assessed. In part 2, 42 fetuses scanned within 72 hours of delivery were followed postnatally. VIMV values were compared between NRDS and non-NRDS neonates, and logistic regression was used to evaluate predictive value. RESULTS: MV-Flow successfully visualized fine peripheral lung vessels undetectable by conventional Doppler. VIMV measurements were feasible and highly reproducible (intraclass correlation coefficient >0.92). VIMV increased with gestational age (r≈0.8, P<0.001). Fetuses who developed NRDS had significantly lower VIMV than matched controls (P<0.05). Each 1% increase in VIMV was associated with a 73% (whole lung) or 65% (peripheral lung) reduction in NRDS risk (adjusted odds ratio≈0.3, P<0.005). A low peripheral-lung VIMV, defined by gestational norms, predicted NRDS with 82% sensitivity and 84% specificity. CONCLUSION: MV-Flow offers a non-invasive, reproducible method for assessing fetal lung maturity. VIMV correlates with gestational development and may serve as a novel marker for identifying fetuses at risk of NRDS.