Reply

Abstract

We appreciate Dr Welsh's interest and remarks on our recent study on three-dimensional (3D) ultrasound- and power Doppler-assessed placental vascularity in first-trimester normal and aneuploid fetuses1. Although we agree that caution is necessary in interpreting ‘numerical values derived for flow’ including when, as in the case of our study, an identical ultrasound machine setting is used for all patients, we would like to comment briefly on the two main issues raised by Dr Welsh, namely, the influence of placental position and the number of placental sections analyzed. In evaluating our data we were aware of the possible effects of placental position on the attenuation of power Doppler signals. However, when we analyzed placental vascularization in the 100 control pregnancies, we found, as shown here in Figure 1, no relationship between placental position and the distribution of the vascular indices. This suggests that, at least at 11 + 0 to 13 + 6 weeks, it is not necessary to standardize the vascular measures for placental position. Of course, this may be different later in gestation, or when fetal organs are analyzed, two situations in which the effects of beam path should be taken into account. Distribution of placental vascularization values (vascularization index (VI), flow index (FI) and vascularization flow index (VFI)) in 100 pregnancies with euploid fetuses (control group of Rizzo et al.1) according to placental position (anterior, n = 29; posterior, n = 27; lateral, n = 44). Analysis of variance did not indicate significant differences for the vascular indices tested. We further tested the effect of varying the number of placental sections by analyzing 20 consecutive placental volumes in which the vascular indices were calculated on a sequence of 12, 20 and 30 sections, obtained after rotations from the previous section of 15°, 9° and 6°, respectively (Figure 2). Since analysis of variance for repeated measurements did not show significant differences between the three methods, we chose the one using the fewest sections in order to reduce the time required for analysis. Effects of the number of placental sections performed (12, 20 or 30) on the calculation of vascular indices in 20 placental volumes. Individual values are connected by lines. There were no significant differences when analysis of variance for repeated measurements was applied. the evidence found in our study of an increase in placental vascularity with advancing gestation consistent with histological data as shown by a progressive increase in placental flow indices during the early second trimester of pregnancy; the lower vascularization values found in the placenta of trisomy 13 and trisomy 18 fetuses, syndromes characterized by decreased vascularization and trophoblastic hypoplasia; recent data from other groups2 showing that the prognostic value of VOCAL-assessed lung vascularity in fetuses with diaphragmatic hernia is higher compared with that of conventional two-dimensional (2D) and 3D sonographic parameters. With all due respect to the fine work of Dr Welsh and other groups3, 4, we found their approach difficult to apply in clinical practice. We are therefore inclined to continue following our technique until internal standardizing methods become available. G. Rizzo*, D. Arduini*, * Department of Obstetrics and Gynecology, Università Roma Tor Vergata, Roma, Italy