Pulmonary Hypoplasia: Prediction with Use of Ratio of MR Imaging–measured Fetal Lung Volume to US-estimated Fetal Body Weight

To determine the ratio of fetal lung volume (FLV) to fetal body weight (FBW) by using ultrasonography (US) and magnetic resonance (MR) imaging and to evaluate the usefulness of this ratio in predicting pulmonary hypoplasia (PH) in fetuses at high risk.MR imaging lung volumetry and US biometry were performed in 90 fetuses at 25-39 weeks gestation. In the control group of 73 fetuses, normal lung development was confirmed at neonatal follow-up and the normative ratio of MR imaging-measured FLV to US-estimated FBW (FLV/FBW) was determined. The high-risk group included 17 fetuses at risk for PH. The FLV/FBW was compared between the control and high-risk groups and with US parameters for predicting the development of PH in the high-risk group. Measurements 2 or more standard deviations below the mean control group measurement were considered abnormal. Comparisons of the FLV/FBW between groups were made by using the Student t test. The association between development of PH and measurement of each parameter was analyzed by using the Fisher exact probability test.In the control group, the FLV/FBW decreased with gestational age during the third trimester and had a normal distribution (mean ratio, 0.028 mL/g; range, 0.015-0.444 mL/g). The mean FLV/FBW for the nine fetuses with PH (0.012 mL/g +/- 0.008) was significantly lower (P.001) than that for the control group (0.028 mL/g +/- 0.007). Fetuses with abnormal FLV/FBW values were at significantly greater risk (P.05) for PH development. Abnormal FLV/FBW values had higher diagnostic accuracy than abnormal US parameters. Sensitivity of the FLV/FBW was 89% (eight of nine fetuses); specificity, 88% (seven of eight fetuses); positive predictive value, 89% (eight of nine fetuses); negative predictive value, 88% (seven of eight fetuses); and accuracy, 88% (15 of 17 fetuses).The FLV/FBW reflects the adequacy of intrauterine lung growth and can help predict PH.