MRI Reference Ranges for Fetal Cardiothoracic Ratio of Diameter, Area, and Circumference from 21 to 38 Weeks Gestational Age

Abstract

BackgroundWhether fetal cardiothoracic ratio (CTR) is constant or increasing with gestational age (GA) is controversial. The majority of the fetal CTR data has been obtained through ultrasound.PurposeTo retrospectively analyze CTR of diameter, area, and circumference on prenatal MR images in a low‐risk population of singleton pregnancies, and to clarify its diagnostic value.Study TypeRetrospective.Subjects1024 low‐risk singleton pregnancies undergoing MRI.Field StrengthBalanced steady state free precession sequence and single shot‐fast spin echo sequence at 1.5 Tesla.AssessmentPregnancy clinical data were recorded and diameter, area, and circumference of the fetal heart and thorax were measured by two researchers with 6 and 7 years of radiology experience, respectively, and their variation with GA was investigated. The relationship between CTRs with GA was also investigated. Finally, the value of CTR in the diagnosis of fetuses with abnormal development was explored by using receiver operating characteristic (ROC) curves.Statistical TestsLinear regression and ROC curves. A P value <0.05 was considered significant.ResultsThere were significant positive linear correlations (R2 > 0.7, P < 0.0001) between the diameter, area, and circumference of the heart and thorax with GA. The CTRs remain constant values and do not change with GA. The 5th, 50th, and 95th percentiles of the CTR in 21–38 weeks GA were 0.32, 0.39, and 0.48 respectively. The corresponding percentiles for the area ratio were 0.15, 0.21 and 0.27, respectively, and for the circumference ratio were 0.40, 0.46, and 0.52, respectively. Based on ROC curves of CTR with three methods, the area under curves (AUCs) were up to 0.95, the sensitivity and the specificity were more than 88%.Data ConclusionReference ranges of fetal CTR were established using MRI, which remain constant. These may be helpful in making a definitive diagnosis in fetuses with abnormal development.Level of Evidence4.Technical EfficacyStage 2.