The aortic isthmus: A significant yet underexplored watershed of the fetal circulation

The aortic isthmus (AoI) is a unique fetal watershed with a waveform reflecting its complex haemodynamic physiology. The systolic component represents left and right ventricular systolic ejection, and the diastolic component represents comparative downstream vascular impedance between the brachiocephalic and subdiaphragmatic fetal circulations. Several indices have been devised to quantify different components of the waveform, including the pulsatility index, resistance index, isthmic flow index, and recently the isthmic systolic index. There have been promising preliminary studies applying these indices to both cardiac (congenital) and extracardiac pathologies, including intrauterine growth restriction and twin-twin transfusion syndrome. However, the waveform's multifactorial origin has proven to be challenging, and the difficulty in separating various components of the waveform could explain that AoI evaluation does not have a clear clinical utility. Further research is underway to realise the full potential of this vessel in fetal cardiac and haemodynamically compromised pathological conditions. In this review article we outline the physiological origin of this Doppler waveform, describe in detail the various published indices, summarise the published literature to date, and finally outline potential future research and hopefully clinical applications. © 2016 S. Karger AG, Basel. Copyright: All rights reserved

Is there a measurable difference between the left and right modified myocardial performance indices, and does this change to reflect unilateral myocardial dysfunction in pathology?

Introduction: Fetal cardiac dysfunction may manifest itself unilaterally as right and left ventricles differing in design, function and load, measurable as differing in myocardial performance indices (MPIs). We wished to define this difference ('delta-MPI' or DMPI), present its normal range and pilot its use in pathological pregnancy. Material and Methods: Prospective cross-sectional study of 324 normal singleton fetuses (16-38 weeks of gestation). Left and right modified MPI (LMPI and RMPI) were performed during a single examination using the 'peak' valve click technique. Thirty-seven pathological singleton and monochorionic diamniotic twin pregnancies were compared as pilot data. Results: Modified MPIs (mean ± SD) were 0.45 ± 0.06 (LMPI) and 0.47 ± 0.09 (RMPI), being similar at 18 weeks' gestation with DMPI increasing slightly throughout pregnancy (0.02 ± 0.08). Both singleton intrauterine growth restriction (IUGR) and recipient twin-twin transfusion syndrome (TTTS) showed significantly elevated RMPI, LMPI and DMPI, most pronounced for DMPI (450 and 500% increase, respectively; p < 0.01). DMPI acquisition rates were 83.3% normal and 87.0% pathological. Discussion: We demonstrate for the first time differing intrafetal LMPI and RMPI in a large gestational cohort, with this difference increasing with gestational age. Pilot data confirm the potential for DMPI as a tool to assess unilateral myocardial function in singleton IUGR and recipient twins in TTTS, and further studies are under way to evaluate its clinical utility. © 2015 S. Karger AG, Basel

Use of the foetal myocardial performance index in monochorionic, diamniotic twin pregnancy: A prospective cohort and nested case-control study

Aims: Assess clinical utility of the foetal Myocardial Performance Index (MPI) in evaluation and management of monochorionic, diamniotic twin (MCDA) pregnancies. Methods: Prospective cohort of (a) initially uncomplicated MCDA (b) Complicated MCDA, including twin–twin transfusion syndrome (TTTS), selective intrauterine growth restriction (sIUGR), and liquor and/or growth discordance (L/GD) not meeting TTTS or sIUGR criteria. TTTS and sIUGR were case-control matched. Routine Dopplers and MPI were taken and correlated to diagnosis and final outcome. Results: Twenty-six always uncomplicated pairs, 51 always complicated pairs, and seven uncomplicated to pathological pairs were included. TTTS recipient (n = 25) left and right MPI and intertwin difference (ITD) were significantly elevated, however, were already elevated in Stage I (n = 10), and did not predict progression or pregnancy outcome. sIUGR MPI (n = 11) did not differ significantly from control. Of 15-L/GD pairs, two that progressed to TTTS had significantly higher left and right MPI values in the future recipient (0.61 and 0.72) versus future sIUGR larger twins (0.48 and 0.51) or stable L/GD (0.47 and 0.52): p <.01 for all comparisons. Conclusions: In this cohort, MPI did not add substantial diagnostic/prognostic information to current routine evaluation in established TTTS or sIUGR though potentially differentiated L/GD cases progressing to TTTS. © 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group

Use of the myocardial performance index in decreased fetal movement assessment: A case-control study

Objectives: To determine whether there are any fetal cardiac function changes, as measured by the myocardial performance index (MPI), in pregnancies complicated by decreased fetal movement (DFM). Methods: We performed a prospective cross-sectional case-control study of 50 DFM and 50 uncomplicated third-trimester pregnancies matched within 2 gestational weeks. Routine ultrasound growth and well-being parameters as well as MPI were measured. Average MPI measurements and its component values were compared between the DFM and the control group, as were demographics, other ultrasound data, and perinatal outcomes. Results: Average left MPI (LMPI) and right MPI (RMPI) was similar between groups (LMPI: 0.54 ± 0.08 [DFM], 0.53 ± 0.08 [controls], p = 0.76; RMPI: 0.60 ± 0.12 (DFM), 0.59 ± 0.11 [controls], p = 0.79). However, subgroup analysis of DFM fetuses with (n = 20) or without (n = 30) any adverse perinatal outcome demonstrated modestly higher average RMPI and LMPI in the adverse perinatal outcome group (RMPI: 0.64 ± 0.08 vs. 0.57 ± 0.13, p = 0.02; LMPI: 0.56 ± 0.07 vs. 0.52 ± 0.07, p = 0.052). Conclusion: The MPI did not demonstrate clinically usable differences between the overall DFM population and controls. However, higher LMPI and RMPI values in the exploratory subgroup of DFM fetuses with adverse perinatal outcomes may warrant further exploration of the MPI in DFM. © 2017 S. Karger AG, Basel

The influence of hyperoxygenation on fetal brain vascularity measured using 3D power doppler ultrasound and the index “fractional moving blood volume”

Introduction: Maternal hyperoxygenation effects on fetal cerebral hemodynamics are largely unknown. This study aimed to determine efficacy and reliability of a validated power Doppler ultrasound (US) index, fractional moving blood volume (FMBV), at measuring fetal cerebral vasculature changes during maternal hyperoxia. Methods: The fetal cerebral effects of 10 min of hyperoxygenation at 2 flow rates (52%/60% FiO2) were evaluated in women in their third trimester of pregnancy. 2D-US and 3D-US in a transverse plane were performed before, during, and following maternal hyperoxygenation with FMBV estimation performed offline. Results: Forty-five cases provided data for analysis. Mean intraobserver ICCs were 0.89 (3D-FMBV) and 0.84 (2D-FMBV). A significant difference in vascularity before and during and before and after 60% hyperoxia was observed (p 0.05). Significant differences in vascularity were found between 2D-FMBV and 3D-FMBV (p < 0.01). Conclusion: Measurement of fetal cerebral vascularity by 3D-FMBV and 2D-FMBV was highly reproducible. The differing cerebral vascular changes seen with 60% but not 52% FiO2 suggest a possible “threshold effect” that may have influenced prior studies. Further studies are needed to assess cerebral effects of maternal hyperoxygenation on compromised fetuses

Applying spatial-temporal image correlation to the fetal kidney: Repeatability of 3D segmentation and volumetric impedance indices

Introduction: Spatiotemporal image correlation (STIC) can evaluate fetal renal impedance using four‐dimensional volumetric indices. We assessed repeatability of three‐dimensional kidney segmentation and the repeatability of the resultant indices. Methods: In each of 57 healthy pregnant women, three renal artery pulsed‐wave Doppler (PWD) traces and three STIC volumes were acquired from the same fetal kidney and segmented by two observers. Vascularisation‐flow index (VFI) and fractional moving blood volume (FMBV) were calculated for every STIC frame and used to determine the volumetric pulsatility index (vPI), volumetric resistance index (vRI) and volumetric systolic/diastolic ratio (vS/D). Segmentation performance was assessed using Dice similarity coefficients (DSCs), Hausdorff distances, coefficient of variation (CoV) and the intraclass correlation coefficient (ICC). Intra/Inter volumetric index repeatability was assessed using ICCs. Results: Forty‐eight cases (84%) provided full data. Mean intra‐ and interobserver DSCs were 0.90 and 0.81. Mean intra‐ and interobserver Hausdorff distances were 3.88 mm and 5.27 mm. Average kidney volumes for observers 1 and 2 were 9.88 mL and 8.54 mL (mean difference 16.1%). Mean intra‐observer volumetric CoVs were 5.3% and 8.1%. Intra‐ and interobserver ICCs for kidney volume (same STIC volume) were 0.97 and 0.85. When assessing volume variation between STIC volumes, intra‐observer ICC was 0.97. ICCs were 0.77–0.81 for VFI‐derived volumetric indices and 0.61–0.62 for FMBV‐derived indices; ICCs for all PWD indices were between 0.58 and 0.59. Conclusions: Periodical variation in vascularity was demonstrated in the fetal kidney, and three‐dimensional segmentation was highly repeatable. Derived volumetric impedance indices show moderate variability but outperform corresponding two‐dimensional PWD indices in terms of reproducibility