453 The vaginal fluid index (VFI), a hidden 5th amniotic fluid pocket

Abstract

Abnormal amniotic fluid volume has been associated with a variety of adverse pregnancy outcomes. Transabdominal ultrasound is used to assess quantitatively the amniotic fluid volume, by either the amniotic fluid index (AFI) or the maximum vertical pocket (MVP) methods. The fore-bag is a pocket of hidden amniotic fluid preceding the fetal presenting part. Its dimensions and significance have not been studied. In this feasibility study, we described the transvaginal measurements of the this fore-bag, and assessed its correlation with the standard AFI and MVP. A prospective observational study between July 2018 and July 2020. Eligible cases were non-laboring women with singleton pregnancies, vertex presentation and normal AFI at 36-41 weeks’ gestation. The AFI and MVP were obtained abdominally from the biophysical profile. Feasibility was assessed by using the transvaginal ultrasound to measure the three orthogonal planes of the fore-bag (Figure 1). The vaginal fluid index (VFI) was defined as the volume composite of the vertical, horizontal and axial vaginal measurements. Correlations of the fore-bag measurements with both AFI and MVP were then calculated. During the recruitment process, 292/305 (95.7%) women were enrolled. Their demographic and ultrasound characteristics are given in table 1. All participants completed both transabdominal and transvaginal ultrasound, of which the vaginal pocket was demonstrated in 266/292 (91.1%) of cases. We found a significant correlation, for nulliparous and multiparous, between the individual vaginal pocket measurements and the VFI, to both the AFI and MVP measurements (R=0.35, p<0.001; R=0.34, p<0.001, respectively). We introduced a new transvaginal ultrasound variable, the VFI, which was feasible to measure in the majority of women. The VFI may provide invaluable information into the future decision-making around the time of delivery, especially in women with suspected oligohydramnios. A multicenter trial is currently being launched to implement our findings into the traditional AFI.View Large Image Figure ViewerDownload Hi-res image Download (PPT)