Placental Elasticity and Histopathological Findings in Normal and Intra-Uterine Growth Restriction Pregnancies Assessed with Strain Elastography in Ex Vivo Placenta

Value of placental virtual magnetic resonance elastography and intravoxel incoherent motion-based diffusion and perfusion in predicting adverse outcomes of small-for-gestational-age infants

OBJECTIVE

It is critical to early monitor and manage small-for-gestational age (SGA) infants with truly adverse outcomes not detected by conventional methods. We aimed to explore the value of diffusion-weighted imaging (DWI)-based virtual magnetic resonance elastography (vMRE) and intravoxel incoherent motion (IVIM)-based biexponential and stretched exponential parameters in predicting adverse outcomes of SGA infants.

METHODS

Twenty SGA infants with adverse outcomes and forty without adverse outcomes were included in this prospective study. One DWI-based vMRE parameter [the stiffness value (μdiff)], five IVIM-based parameters [true diffusion coefficient (D), pseudo-diffusion coefficient (D*), perfusion fraction (f), diffusion distribution coefficient (DDC), and diffusion heterogeneity index (Alpha)] and apparent diffusion coefficient (ADC) were calculated and compared between groups. The predictive efficiency was compared by the logistic regression analysis and receiver operating characteristic curve analysis. The relationship between the μdiff value with gestational age was also evaluated.

RESULTS

The placental μdiff value was remarkably higher, and the f, DDC, and ADC values were considerably lower in the SGA infants with adverse outcomes compared with those without adverse outcomes. The μdiff and f value were predictive risk factors for SGA infants with adverse outcomes. A combined predictive model (μdiff and f) improved the predictive efficacy. Moreover, there was no statistically significant correlation between the placental stiffness value and gestational age.

CONCLUSIONS

Functional MRI parameters to quantify placenta elastography and microcirculation in SGA patients. This might be a useful tool to assess placental function and a vital non-invasive supplement for predicting adverse outcomes of SGA infants.

CRITICAL RELEVANCE STATEMENT

This prospective study shows DWI-based virtual magnetic resonance elastography and intravoxel incoherent motion-based functional parameters to quantify placenta elastography and microcirculation in small-for-gestational-age patients, which could complement existing non-invasive methods for monitoring and predicting neonatal perinatal adverse outcome.

KEY POINTS

• vMRE is an emerging non-invasive imaging technique for evaluating placenta stiffness. • SGA infants with adverse outcome have stiffer placental elasticity and lower microcirculation. • Risk factors combination displayed better efficacy in predicting adverse outcomes of SGA.

Early Prediction of Gestational Diabetes Mellitus Using Placental Strain Elastography and Subcutaneous Adipose Tissue Thickness

AIM

The aim of this study is to investigate the efficacy of placental strain ratio values measured by real-time sonoelastography and maternal subcutaneous adipose tissue thickness measured by two-dimensional ultrasonography in predicting gestational diabetes mellitus in the first trimester.

MATERIALS AND METHODS

The population of the study consisted of the first 210 consecutive singleton pregnant women who applied for routine first-trimester screening between the 11th and 14th week of gestation.B-mode subcutaneous adipose tissue thickness sonography and real-time placental strain elastography scanning were performed.All patients underwent 75 g oral glucose tolerance test between the 24th and 28th week of gestation. American Diabetes Association criteria were used in the diagnosis of gestational diabetes mellitus.

RESULTS

It was observed that body mass index (p<0.001), first-trimester fasting blood sugar (p<0.001), subcutaneous adipose tissue thickness (p<0.001), and placental strain ratio value (p<0.001) affected the development of gestational diabetes mellitus statistically. The multivariate analysis shown that subcutaneous adipose tissue thickness (odds ratio=1.271, 95% CI=1.142-1.416, p<0.001) and placental strain ratio value (odds ratio=3.664, 95% CI=1.927-6.969, p<0.001) were the independent risk factors affecting the development of gestational diabetes mellitus.

CONCLUSIONS

The findings of this study indicated a positive correlation between 75 g oral glucose tolerance test application and first trimester subcutaneous adipose tissue thickness and placental strain ratio. Using the cut-off values of>11.5 mm for subcutaneous adipose tissue and>0.986 for placental strain ratio, the development of gestational diabetes mellitus may be predicted in the early weeks of pregnancy.

SWAVE 2.0 Imaging of Placental Elasticity and Viscosity: Potential Biomarkers for Placenta-Mediated Disease Detection

Pregnancy complications such as pre-eclampsia (PE) and intrauterine growth restriction (IUGR) are associated with structural and functional changes in the placenta. Different elastography techniques with an ability to assess the mechanical properties of tissue can identify and monitor the pathological state of the placenta. Currently available elastography techniques have been used with promising results to detect placenta abnormalities; however, limitations include inadequate measurement depth and safety concerns from high negative pressure pulses. Previously, we described a shear wave absolute vibro-elastography (SWAVE) method by applying external low-frequency mechanical vibrations to generate shear waves and studied 61 post-delivery clinically normal placentas to explore the feasibility of SWAVE for placental assessment and establish a measurement baseline. This next phase of the study, namely, SWAVE 2.0, improves the previous system and elasticity reconstruction by incorporating a multi-frequency acquisition system and using a 3-D local frequency estimation (LFE) method. Compared with its 2-D counterpart, the proposed system using 3-D LFE was found to reduce the bias and variance in elasticity measurements in tissue-mimicking phantoms. In the aim of investigating the potential of improved SWAVE 2.0 measurements to identify placental abnormalities, we studied 46 post-delivery placentas, including 26 diseased (16 IUGR and 10 PE) and 20 normal control placentas. By use of a 3.33-MHz motorized curved-array transducer, multi-frequency (80,100 and 120 Hz) elasticity measures were obtained with 3-D LFE, and both IUGR (15.30 ± 2.96 kPa, p = 3.35e^-5) and PE (12.33 ± 4.88 kPa, p = 0.017) placentas were found to be significantly stiffer compared with the control placentas (8.32 ± 3.67 kPa). A linear discriminant analysis (LDA) classifier was able to classify between healthy and diseased placentas with a sensitivity, specificity and accuracy of 87%, 78% and 83% and an area under the receiver operating curve of 0.90 (95% confidence interval: 0.8-0.99). Further, the pregnancy outcome in terms of neonatal intensive care unit admission was predicted with a sensitivity, specificity and accuracy of 70%, 71%, 71%, respectively, and area under the receiver operating curve of 0.78 (confidence interval: 0.62-0.93). A viscoelastic characterization of placentas using a fractional rheological model revealed that the viscosity measures in terms of viscosity parameter n were significantly higher in IUGR (2.3 ± 0.21) and PE (2.11 ± 0.52) placentas than in normal placentas (1.45 ± 0.65). This work illustrates the potential relevance of elasticity and viscosity imaging using SWAVE 2.0 as a non-invasive technology for detection of placental abnormalities and the prediction of pregnancy outcomes.

Placental abnormalities in type 1 and type 2 diabetes mellitus: a systematic review and metaanalysis of shear wave elastography

OBJECTIVE

This study aimed to describe the placental changes occurring in women with preexisting diabetes mellitus and to determine if elastography can detect placental changes in vivo.

DATA SOURCES

PubMed, Embase, Medline, and Cochrane were searched to identify English language studies published until July 2020.

STUDY ELIGIBILITY CRITERIA

1) For key question 1, studies that described histopathologic changes in placentas from women with known diabetes mellitus and 2) for key question 2, those that described structural-placental changes detectable by elastography in high-risk pregnancies (eg, those complicated by preeclampsia and/or fetal growth restriction), were included.

METHODS

For key question 1, we grouped placental pathologies using the Amsterdam International Consensus Group definitions. For key question 2, we conducted a metaanalysis including all data from studies reporting placental stiffness in meters per second (m/s) or kilopascals (kPa). The mean difference (95% confidence interval) was calculated using a random effects model.

RESULTS

Data were extracted from 14 studies of placental histopathology in women with known diabetes. In this group, a wide variety of placental histopathologic changes are described, though none are considered pathognomonic. The histopathologic changes including maternal vascular malperfusion, fetal vascular malperfusion, and/or infectious/inflammatory/other changes were divided into 3 broad categories on the basis of presumed etiology. A total of 15 studies reported the placental stiffness scores in women with a high-risk pregnancy vs those with a normal pregnancy. Only 1 reported stiffness scores for placentas in women with preexisting diabetes mellitus (N<10 women). Pooled analysis of 14 studies with available data included 478 "high-risk pregnancies" and 828 control or healthy pregnancies. Maternal-derived pathologies resulted in higher placental stiffness (mean difference 4.5 kPa [95% confidence interval, 3.16-5.87]) compared with control or healthy pregnancies. Fetal-derived pathologies also resulted in higher placental stiffness (mean difference of 6.5 kPa [95% confidence interval, 1.08-11.86]) compared with control or healthy pregnancies.

CONCLUSION

Shear wave elastography may provide an in vivo approximation of placental histopathology in women with certain kinds of high-risk pregnancies. A high-risk pregnancy may involve maternal- and fetal-derived pathologies. Further studies, particularly in women with preexisting diabetes, are needed to confirm this observation.

A Review of Biomechanics Analysis of the Umbilical-Placenta System With Regards to Diseases

Placenta is an important organ that is crucial for both fetal and maternal health. Abnormalities of the placenta, such as during intrauterine growth restriction (IUGR) and pre-eclampsia (PE) are common, and an improved understanding of these diseases is needed to improve medical care. Biomechanics analysis of the placenta is an under-explored area of investigation, which has demonstrated usefulness in contributing to our understanding of the placenta physiology. In this review, we introduce fundamental biomechanics concepts and discuss the findings of biomechanical analysis of the placenta and umbilical cord, including both tissue biomechanics and biofluid mechanics. The biomechanics of placenta ultrasound elastography and its potential in improving clinical detection of placenta diseases are also discussed. Finally, potential future work is listed.

Can placental elasticity predict the time of delivery in cases of threatened preterm labor?

AIM

We aimed to evaluate placental elasticity for the short-time prediction of delivery in cases of threatened preterm labor (TPL).

METHODS

We performed a prospective study with consented pregnant women diagnosed with TPL (24th to 34th gestational week). According to the birth time, the patients were grouped into two groups, whether the delivery happened in the following first week or not. We compared the placental strain ratio (PSR) values between these two groups.

RESULTS

A total of 108 pregnant women divided into two groups according to the delivery time were enrolled in our study. The pregnant women who had a delivery in 1 week after hospitalization have increased PSR values when compared to those who have not delivered within 1 week (P < 0.001). Multivariate logistic regression analysis showed that cervical length and PSR were significantly associated with delivery in 1 week after hospitalization. When the cervical length was entered as a covariate (control) variable, PSR was significantly associated with delivery time (B = 0.504, odds ratio: 1.655, 95% confidence interval: 1.339-2.045, P < 0.001). A PSR value of 4.04 had a sensitivity of 77.78% and a specificity of 87.04% in terms of short-time prediction of the delivery time, in the receiver-operator curves analysis to determine the cut-off point PSR value.

CONCLUSION

Elastography may contribute to predict the delivery time in high-risk pregnants with TPL.

The effect of maternal vitamin D levels on placental shear wave elastography findings in the first trimester

The aim of this study was to investigate the effect of maternal serum Vitamin D levels on the elasticity of placenta. Seventy-four spontaneously conceived singleton pregnancies in their first trimester were enrolled into this study. Fifty-one of them had Vitamin D deficiency (<20 ng/mL), while 23 pregnancies had Vitamin D levels ≥20 ng/mL. The placental elasticity was measured by the transabdominal Point Shear Wave Elastography (pSWE) method. In each case, the mean of 10 consecutive measurements was accepted as the mean placental elasticity value. The mean pSWE values did not significantly differ between the Vitamin D deficient group and the control group (p > .05). Placental elasticity was not found to be different in the pregnancies with Vitamin D deficiency during the first trimester.IMPACT STATEMENTWhat is already known on this subject? The pSWE technique provides opportunity to determine the elasticity of any interested tissue. Placental elasticity has been found to be changed in inflammatory and fibrotic conditions such as in preeclampsia, intrauterine growth restriction or diabetes. On the other hand, Vitamin D deficiency is linked with several comorbidities such as autoimmune disorders, cancer and cardiovascular disorders. Vitamin D also plays a role in placental angiogenesis in the first trimester. Maternal Vitamin D levels are shown to be related with adverse pregnancy outcomes.What do the results of this study add? To the best of our knowledge, this study is the first assessing the association between Vitamin D levels and placental elasticity. Placental elasticity was not found to be changed by Vitamin D deficiency.What are the implications of these findings for clinical practice and/or further research? Our pilot study revealed that Vitamin D deficiency does not have any impact on placental elasticity in the first trimester. However, longitudinal studies concerning placental elasticity in subsequent trimesters are needed to support our findings.

The use of elastography in placental research - A literature review

INTRODUCTION

Ultrasound elastography is a technique used to quantify biomechanical changes that occur in parenchymal tissue with disease. Recent research has applied the technique to the placenta in order to investigate changes associated with uteroplacental dysfunction. We performed a literature review to summarise the current available information regarding this novel technique.

METHODS

Pubmed, CINAHL and Embase were searched using the terms "placenta", "ultrasound" and "elastography". Only full text studies written in English and limited to placental sonoelastography were included.

RESULTS

Twenty-eight studies met the inclusion criteria and were included in this review. Publications were divided into in vivo and ex vivo groups, and further categorised into four subgroups: normal pregnancy, pregnancy-induced hypertension and pre-eclampsia, fetal growth restriction and other pregnancy complications.

CONCLUSION

Ultrasound elastography can quantitatively assess biomechanical properties of the placenta in conditions where placental function is compromised.

Comparison of placental elasticity in normal and intrauterine growth retardation pregnancies by ex vivo strain elastography

OBJECTIVE

To compare the placental elasticity in fetuses with or without intrauterine growth restriction (IUGR).

MATERIALS AND METHODS

One hundred pregnant women (50 IUGR and 50 healthy) with anteriorly located placenta were evaluated during the third trimester of pregnancy. Measurements were carried out by a machine that has a real-time elastographic ultrasonography feature. After obtaining the optimum image, three areas (subcutaneous tissue, center, and the edge of the placenta) were provided to identify the placental strain values. Then, the placental strain ratio (PSR) value was calculated automatically. Two groups compared in terms of their PSR values.

RESULTS

There was a significant difference in placental elasticity between the groups (P < 0.001). PSR value was 2.8 ± 1.2 in the IUGR group and 1.3 ± 0.6 in the control group. A PSR value of 1.78 had an 86% sensitivity (OR 4.3) and 80% specificity (OR 0.17) in IUGR cases. The positive predictive value was 81.1% and the negative predictive value was 85.1% for this cut-off value.

CONCLUSIONS

We have shown that placental strain ratio is increased during the third trimester of pregnancy in fetuses with IUGR. Increased stiffness and elasticity may be responsible for the onset of IUGR in some cases.

Placental elasticity assessment by point shear wave elastography in pregnancies with intrauterine growth restriction

Background Placental elasticity varies in different diseases. Our objective was to evaluate placental elasticity using point shear wave elastography (pSWE) in pregnancies with intrauterine growth restriction (IUGR). Methods A total of 66 pregnant women with IUGR and 81 healthy pregnant women were enrolled. Placental elasticity was measured using the transabdominal pSWE method. Ten measurements were made, and the mean was accepted as the mean placental elasticity value in each case. The results for IUGR pregnancies and controls were compared. Results The mean pSWE values were significantly higher in pregnancies with IUGR, which means that women with IUGR have stiffer placentas (P < 0.001). Furthermore, the pSWE values were significantly and positively correlated with Doppler indices and adverse perinatal outcomes. Conclusion The pregnancies with IUGR had stiffer placentas than the healthy controls. The utilization of pSWE for placental elasticity may be useful in the diagnosis and management of IUGR as a supplement to the existing ultrasonography methods.

Drug transport across the human placenta: review of placenta-on-a-chip and previous approaches

In the past few decades, the placenta became a very controversial topic that has had many researchers and pharmacists discussing the significance of the effects of pharmaceutical drug intake and how it is a possible leading cause towards birth defects. The creation of an in vitro microengineered model of the placenta can be used to replicate the interactions between the mother and fetus, specifically pharmaceutical drug intake reactions. As the field of nanotechnology significantly continues growing, nanotechnology will become more apparent in the study of medicine and other scientific disciplines, specifically microengineering applications. This review is based on past and current research that compares the feasibility and testing of the placenta-on-a-chip microengineered model to the previous and underdeveloped in vivo and ex vivo approaches. The testing of the practicality and effectiveness of the in vitro, in vivo and ex vivo models requires the experimentation of prominent pharmaceutical drugs that most mothers consume during pregnancy. In this case, these drugs need to be studied and tested more often. However, there are challenges associated with the in vitro, in vivo and ex vivo processes when developing a practical placental model, which are discussed in further detail.

Multiparametric QUS Analysis for Placental Tissue Characterization

Multiparametric Quantitative Ultrasound (QUS) holds promise for characterizing placental tissue and detecting placental disorders. In this study, we simultaneously extract two qualitatively different QUS parameters, namely attenuation coefficient estimate (ACE) and shear wave speed from ultrasound radio frequency data acquired using a shear wave vibro elastography (SWAVE) method. The study comprised data from 59 post-delivery clinically normal placentas. The shear wave speed was found to be equal to 1.74 ± 0.13 m/s whereas the attenuation coefficient estimate was 0.57 ± 0.48 dB/cm-MHz. This provides a baseline for future studies of placental disorders.

Altered Placental Chorionic Arterial Biomechanical Properties During Intrauterine Growth Restriction

Intrauterine growth restriction (IUGR) is a pregnancy complication due to placental dysfunction that prevents the fetus from obtaining enough oxygen and nutrients, leading to serious mortality and morbidity risks. There is no treatment for IUGR despite having a prevalence of 3% in developed countries, giving rise to an urgency to improve our understanding of the disease. Applying biomechanics investigation on IUGR placental tissues can give important new insights. We performed pressure-diameter mechanical testing of placental chorionic arteries and found that in severe IUGR cases (RI > 90th centile) but not in IUGR cases (RI < 90th centile), vascular distensibility was significantly increased from normal. Constitutive modeling demonstrated that a simplified Fung-type hyperelastic model was able to describe the mechanical properties well, and histology showed that severe IUGR had the lowest collagen to elastin ratio. To demonstrate that the increased distensibility in the severe IUGR group was related to their elevated umbilical resistance and pulsatility indices, we modelled the placental circulation using a Windkessel model, and demonstrated that vascular compliance (and not just vascular resistance) directly affected blood flow pulsatility, suggesting that it is an important parameter for the disease. Our study showed that biomechanics study on placenta could extend our understanding on placenta physiology.

Measurement of shear wave speed dispersion in the placenta by transient elastography: A preliminary ex vivo study

Background

Placental elasticity may be modified in women with placental insufficiency. Shear wave elastography (SWE) can measure this, using acoustic radiation force, but the safety of its use in pregnant women has not yet been demonstrated. Transient elastography (TE) is a safer alternative, but has not yet been applied to the placenta. Moreover, the dispersion of shear wave speed (SWS) as a function of frequency has received relatively little study for placental tissue, although it might improve the accuracy of biomechanical assessment.

Objective

To explore the feasibility and reproducibility of TE for placental analysis, to compare the values of SWS and Young’s modulus (YM) from TE and SWE, and to analyze SWS dispersion as a function of frequency ex vivo in normal placentas.

Materials and methods

Ten normal placentas were analyzed ex vivo by an Aixplorer ultrasound system as shear waves were generated by a vibrating plate and by using an Aixplorer system.

The frequency analysis provided the value of the exponent n from a fractional rheological model applied to the TE method. We calculated intra- and interobserver agreement for SWS and YM with 95% prediction intervals, created Bland-Altman plots with 95% limits of agreement, and estimated the intraclass correlation coefficient (ICC).

Main results

The mean SWS was 1.80 m/s +/- 0.28 (standard deviation) with the TE method at 50 Hz and 1.82 m/s +/-0.13 with SWE (P = 0.912). No differences were observed between the central and peripheral regions of placentas with either TE or SWE. With TE, the intraobserver ICC for SWS was 0.68 (0.50–0.82), and the interobserver ICC for SWS 0.65 (0.37–0.85). The mean parameter n obtained from the fractional rheological model was 1.21 +/- 0.12, with variable values of n for any given SWS.

Conclusions

TE is feasible and reproducible on placentas ex vivo. The frequency analysis of SWS provides additional information about placental elasticity and appears to be able to distinguish differences between placental structures.