Purpose: To prospectively determine normal ranges of total fetal lung volume (TFLV) based on fetal body volume (FBV) and to determine whether prediction of TFLV based on such ranges is independent of fetal biometric indexes.
Materials and methods: The study was approved by the Ethics Committee on Clinical Studies; informed consent was obtained. Magnetic resonance imaging volumetric measurement of fetal lung, liver, and body was performed in 200 fetuses without abnormalities affecting these structures. FBV was assessed with planimetric measurements by using T2-weighted half-Fourier rapid acquisition with relaxation enhancement at 16-40 weeks of gestation. TFLV was correlated to gestational age (GA), liver volume, and FBV. Observed-expected (O/E) ratio for TFLV was calculated by expressing the observed TFLV as a percentage of the expected mean TFLV for GA, liver volume, or FBV. Three groups of fetuses were defined on the basis of biometric percentiles for fetal weight obtained through ultrasonography: fetuses with weight at or below the 5th percentile, those with weight at or above the 95th percentile, and those with weight between these two percentiles (eutrophic). Median O/E ratios, based on GA and FBV, in fetuses with weight below the 5th percentile and in those with weight above the 95th percentile, were compared with median O/E ratio of eutrophic fetuses (Mann-Whitney U test).
Results: TFLV correlated best with FBV, according to the following cubic fit: TFLV = [(2.0 x 10(-9)) x FBV(3)] - [(1.19 x 10(-5)) x FBV(2)] + (0.0508 x FBV) - 1.79 (r(2) = 0.85, P < .001). In 174 eutrophic fetuses, normal median O/E ratio based on GA was 99.1% (range, 31.2%-158.0%), which was higher than that in 11 fetuses with weight at or below the 5th percentile (46.2%; range, 15.7%-87.3%) (P < .01) and lower than that in 15 fetuses with weight at or above the 95th percentile (146.8%; range, 87.2%-204.2%) (P < .01). Normal median O/E ratio, based on FBV, was independent of biometric indexes irrespective of the percentile for fetal weight.
Conclusion: FBV correlated best with TFLV, irrespective of biometric variables.