The objective of this preliminary study was to evaluate three-dimensional ultrasonographic lung volume measurement in the normally developing fetus in the second half of pregnancy. Total fetal lung volume was determined by subtraction of fetal heart volume from thoracic volume, using the perpendicular transverse, sagittal and frontal planes of the fetus. Technically acceptable lung volume measurements were obtained in 29 out of 34 women with an uncomplicated pregnancy. A statistically significant increase in normal fetal lung volume was established with advancing gestational age and with increasing fetal estimated weight, demonstrating an approximately seven-fold rise in fetal lung volume during the second half of pregnancy. Three-dimensional ultrasonography can be applied for estimation of fetal lung volume. Whether this technique is useful in the prenatal prediction of pulmonary hypoplasia remains to be determined.
Three-dimensional ultrasound allows measurement of fetal liver volume, and this demonstrated an approximately 14-fold increase during the second half of pregnancy. It is speculated that three-dimensional fetal liver volume measurement may identify the fetus at risk of growth restriction.
The influence of pulsatile diameter changes on calculation of volume flow has been studied. In vitro studies and an animal study were carried out with a real-time imaging and pulsed Doppler velocity measurement system. For precise pulsatile diameter information a wall motion tracking device was incorporated. Whereas in vitro a high degree of accuracy was found for the measurements of volume flow, this could not be substantiated in the descending aorta of the fetal lamb, in which Doppler volume flow differed between -7.5 and 17% from magnetic volume flow. In a clinical study the relative influence of various diameter approximations on calculated fetal aortic volume flow was assessed in 16 normal third trimester pregnancies. Depending on the selected diameter approximation method it appeared that differences from 19% underestimation to 9% overestimation in calculated volume flow could be obtained when reference was made to volume flow derived from diameter and velocity information.
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