Placental vascular abnormalities in the mouse alter umbilical artery wave reflections

A genetically small fetus impairs placental adaptations near term

The placenta is a gatekeeper between the mother and fetus, adapting its structure and functions to support optimal fetal growth. Studies exploring adaptations of placentae that support the development of genetically small fetuses are lacking. Here, using a mouse model of impaired fetal growth, achieved by deleting insulin-like growth factor 2 (Igf2) in the epiblast, we assessed placental nutrient transfer and umbilical artery (UA) blood flow during late gestation. At embryonic day (E) 15.5, we observed a decline in the trans-placental flux of glucose and system A amino acids (by using 3H-MeG and 14C-MeAIB), proportionate to the diminished fetal size, whereas UA blood flow was normal. However, at E18.5, the trans-placental flux of both tracers was disproportionately decreased and accompanied by blunted UA blood flow. Feto-placental growth and nutrient transfer were more impaired in female conceptuses. Thus, reducing the fetal genetic demand for growth impairs the adaptations in placental blood flow and nutrient transport that normally support the fast fetal growth during late gestation. These findings have important implications for our understanding of the pathophysiology of pregnancies afflicted by fetal growth restriction.

Molecular regulators of defective placental and cardiovascular development in fetal growth restriction

Placental insufficiency is one of the major causes of fetal growth restriction (FGR), a significant pregnancy disorder in which the fetus fails to achieve its full growth potential in utero. As well as the acute consequences of being born too small, affected offspring are at increased risk of cardiovascular disease, diabetes and other chronic diseases in later life. The placenta and heart develop concurrently, therefore placental maldevelopment and function in FGR may have profound effect on the growth and differentiation of many organ systems, including the heart. Hence, understanding the key molecular players that are synergistically linked in the development of the placenta and heart is critical. This review highlights the key growth factors, angiogenic molecules and transcription factors that are common causes of defective placental and cardiovascular development.

Adaptation of a Clinical High-Frequency Transrectal Ultrasound System for Prostate Photoacoustic Imaging: Implementation and Pre-clinical Demonstration

OBJECTIVE

High-frequency, high-resolution transrectal micro-ultrasound (micro-US: ≥15 MHz) imaging of the prostate is emerging as a beneficial tool for scoring disease risk and accurately targeting biopsies. Adding photoacoustic (PA) imaging to visualize abnormal vascularization and accumulation of contrast agents in tumors has potential for guiding focal therapies. In this work, we describe a new imaging platform that combines a transrectal micro-US system with transurethral light delivery for PA imaging.

METHODS

A clinical transrectal micro-US system was adapted to acquire PA images synchronous to a tunable laser pulse. A transurethral side-firing optical fiber was developed for light delivery. A polyvinyl chloride (PVC)-plastisol phantom was developed and characterized to image PA contrast agents in wall-less channels. After resolution measurement in water, PA imaging was demonstrated in phantom channels with dyes and biodegradable nanoparticle contrast agents called porphysomes. In vivo imaging of a tumor model was performed, with porphysomes administered intravenously.

RESULTS

Photoacoustic imaging data were acquired at 5 Hz, and image reconstruction was performed offline. PA image resolution at a 14-mm depth was 74 and 261 μm in the axial and lateral directions, respectively. The speed of sound in PVC-plastisol was 1383 m/s, and the attenuation was 4 dB/mm at 20 MHz. PA signal from porphysomes was spectrally unmixed from blood signals in the tumor, and a signal increase was observed 3 h after porphysome injection.

CONCLUSION

A combined transrectal micro-US and PA imaging system was developed and characterized, and in vivo imaging demonstrated. High-resolution PA imaging may provide valuable additional information for diagnostic and therapeutic applications in the prostate.

Polystyrene micro- and nanoplastics cause placental dysfunction in mice†

Maternal exposure to microplastics and nanoplastics has been shown to result in fetal growth restriction in mice. In this study, we investigated the placental and fetal hemodynamic responses to plastics exposure in mice using high-frequency ultrasound. Healthy, pregnant CD-1 dams were given either 106 ng/L of 5 μm polystyrene microplastics or 106 ng/L of 50 nm polystyrene nanoplastics in drinking water throughout gestation and were compared with controls. Maternal exposure to both microplastics and nanoplastics resulted in evidence of placental dysfunction that was highly dependent on the particle size. The umbilical artery blood flow increased by 48% in the microplastic-exposed group and decreased by 25% in the nanoplastic-exposed group compared to controls (p < 0.05). The microplastic- and nanoplastic-exposed fetuses showed a significant decrease in the middle cerebral artery pulsatility index of 10% and 13%, respectively, compared to controls (p < 0.05), indicating vasodilation of the cerebral circulation, a fetal adaptation that is part of the brain sparing response to preserve oxygen delivery. Hemodynamic markers of placental dysfunction and fetal hypoxia were more pronounced in the group exposed to polystyrene nanoplastics, suggesting nanoplastic exposure during human pregnancy has the potential to disrupt fetal brain development, which in turn may cause suboptimal neurodevelopmental outcomes.

Microplastics exposure: implications for human fertility, pregnancy and child health

Plastics found in our everyday environment are becoming an increasing concern for individual and population-level health, and the extent of exposure and potential toxic effects of these contaminants on numerous human organ systems are becoming clear. Microplastics (MPs), tiny plastic particles, appear to have many of the same biological effects as their plastic precursors and have the compounded effect of potential accumulation in different organs. Recently, microplastic accumulation was observed in the human placenta, raising important questions related to the biological effects of these contaminants on the health of pregnancies and offspring. These concerns are particularly heightened considering the developmental origins of health and disease (DOHaD) framework, which postulates that in utero exposure can programme the lifelong health of the offspring. The current review examines the state of knowledge on this topic and highlights important avenues for future investigation.

The human placenta project: Funded studies, imaging technologies, and future directions

The placenta plays a critical role in fetal development. It serves as a multi-functional organ that protects and nurtures the fetus during pregnancy. However, despite its importance, the intricacies of placental structure and function in normal and diseased states have remained largely unexplored. Thus, in 2014, the National Institute of Child Health and Human Development launched the Human Placenta Project (HPP). As of May 2023, the HPP has awarded over $101 million in research funds, resulting in 41 funded studies and 459 publications. We conducted a comprehensive review of these studies and publications to identify areas of funded research, advances in those areas, limitations of current research, and continued areas of need. This paper will specifically review the funded studies by the HPP, followed by an in-depth discussion on advances and gaps within placental-focused imaging. We highlight the progress within magnetic reasonance imaging and ultrasound, including development of tools for the assessment of placental function and structure.

Allometric scaling relationships in mouse placenta

Fetal growth and maturation are highly intertwined with placental development during pregnancy. Here we used placental vascular morphology measurements (depth and span) as well as the umbilical artery (UA) diameter of previously published studies on three different mouse strains (C57BL6/J, CD-1 and BALB/c), which were exposed to different conditions (combination antiretroviral therapy, chronic maternal hypoxia and malaria infection) at different embryonic days, to test the hypothesis that placental vascularization and specifically the UA size affect conceptus weight. Interaction of each study parameter with embryonic day, strain and exposure to treatments are studied to investigate the stability of the scaling relationships across and/or within strains and conditions. In addition, the effect of UA diameter on the placental growth measurements (depth and span) is studied. These results show that the power-law scaling relationship of conceptus weight and placental depth with the UA diameter is conserved across strains and conditions with the scaling exponent of approximately 3/8 and 5/8, respectively. By contrast, the relationship between conceptus weight and either the placental span or depth is different between strains and conditions, suggesting multiple mechanisms of vascular adaptation.

Assessments of microvascular function in organ systems

Microvascular disease plays critical roles in the dysfunction of all organ systems, and there are many methods available to assess the microvasculature. These methods can either assess the target organ directly or assess an easily accessible organ such as the skin or retina so that inferences can be extrapolated to the other systems and/or related diseases. Despite the abundance of exploratory research on some of these modalities and their possible applications, there is a general lack of clinical use. This deficiency is likely due to two main reasons: the need for standardization of protocols to establish a role in clinical practice or the lack of therapies targeted toward microvascular dysfunction. Also, there remain some questions to be answered about the coronary microvasculature, as it is complex, heterogeneous, and difficult to visualize in vivo even with advanced imaging technology. This review will discuss novel approaches that are being used to assess microvasculature health in several key organ systems, and evaluate their clinical utility and scope for further development.

Fetal Sex and Fetal Environment Interact to Alter Diameter, Myogenic Tone, and Contractile Response to Thromboxane Analog in Rat Umbilical Cord Vessels

Fetal growth needs adequate blood perfusion from both sides of the placenta, on the maternal side through the uterine vessels and on the fetal side through the umbilical cord. In a model of intrauterine growth restriction (IUGR) induced by reduced blood volume expansion, uterine artery remodeling was blunted. The aim of this study is to determine if IUGR and fetus sex alter the functional and mechanical parameters of umbilical cord blood vessels. Pregnant rats were given a low sodium (IUGR) or a control diet for the last 7 days of pregnancy. Umbilical arteries and veins from term (22 day) fetal rats were isolated and set-up in wire myographs. Myogenic tone, diameter, length tension curve and contractile response to thromboxane analog U46619 and serotonin (5-HT) were measured. In arteries from IUGR fetuses, myogenic tone was increased in both sexes while diameter was significantly greater only in male fetuses. In umbilical arteries collected from the control group, the maximal contraction to U46619 was lower in females than males. Compared to the control groups, the maximal response decreased in IUGR male arteries and increased in female ones, thus abolishing the sexual dimorphism observed in the control groups. Reduced contractile response to U46619 was observed in the IUGR vein of both sexes. No difference between groups was observed in response to 5HT in arteries. In conclusion, the change in parameters of the umbilical cord blood vessels in response to a mild insult seems to show adaptation that favors better exchange of deoxygenated and wasted blood from the fetus to the placenta with increased myogenic tone.

Interpretation of wave reflections in the umbilical arterial segment of the feto-placental circulation: computational modeling of the feto-placental arterial tree

Placental vascular abnormalities are associated with a host of pregnancy complications including placenta mediated fetal growth restriction (FGR). Umbilical arterial (UA) Doppler ultrasound velocity waveforms are widely used in the diagnosis of underlying placental vascular abnormalities in pregnancies with suspected FGR, which greatly help prevent stillbirth via ongoing fetal monitoring and timely delivery. However, the sensitivity of UA Doppler diagnosis diminishes late in gestation. Our goal was to present a generalized wave decomposition method to compute forward and reflected components from UA waveforms. A detailed anatomical based model was also developed to explain observed UA flow waveform and to explore how vascular properties affect the shape of flow wave components. Using pregnant mice and high frequency ultrasound microscopy, we obtained in utero Doppler and M- mode ultrasound measurements in 15 fetuses UA. Following ultrasound, the placentas were collected and perfused with contrast agent to obtain high-resolution 3D images of the feto-placental arteries. Model results indicate the significant role of terminal load impedance (capillary and/or veins) in creating positive or negative reflected waveforms. A negative reflected waveform is obtained when terminal impedance increases. This is consistent with the elongated and non-branching terminal villi that are proposed cause the highly abnormal UA waveforms found in early-onset FGR. The significance of these findings for the diagnostic utility of UA Doppler in human pregnancy is that the identification and measurement of wave reflections may aid in discriminating between healthy and abnormal placental vasculature in pregnancies with suspected late-onset FGR.

Wave reflections in the umbilical artery measured by Doppler ultrasound as a novel predictor of placental pathology

Background

The umbilical artery (UA) Doppler pulsatility index is used clinically to detect elevated feto-placental vascular resistance. However, this metric is confounded by variation in fetal cardiac function and is only moderately predictive of placental pathology. Our group developed a novel ultrasound methodology that measures wave reflections in the UA, thereby isolating a component of the Doppler signal that is specific to the placenta. The present study examined whether wave reflections in the UA are predictive of placental vascular pathology.

Methods

Standard clinical Doppler ultrasound of the UAs was performed in 241 pregnant women. Of these, 40 women met narrowly defined preset criteria for the control group, 36 had maternal vascular malperfusion (MVM) and 16 had fetal vascular malperfusion (FVM). Using a computational procedure, the Doppler waveforms were decomposed into a pair of forward and backward propagating waves.

Findings

Compared to controls, wave reflections were significantly elevated in women with either MVM (p<0.0001) or FVM pathology (p = 0.02). In contrast, the umbilical and uterine artery pulsatility indices were only elevated in the MVM group (p<0.0001) and there were no differences between women with FVM and the controls.

Interpretation

The measurement of wave reflections in the UA, combined with standard clinical ultrasound parameters, has the potential to improve the diagnostic performance of UA Doppler to detect placental vascular pathology. Identifying women with FVM pathology is particularly challenging prenatally and future investigations will determine if women at risk of this specific placental disease could benefit from this novel diagnostic technique.

Real-time Assessment of the Development and Function of the Placenta Across Gestation to Support Therapeutics in Pregnancy

The placenta is vital to the health and development of the fetus, serving to deliver oxygen and nutrients, facilitate the removal of waste products, and provide a barrier to pathogens and other harmful substances present in the maternal circulation. When these processes fail to operate normally, they can lead to complications of pregnancy such as preeclampsia or fetal growth restriction. The development of novel therapeutics for the mother, fetus, or placenta requires a mechanistic understanding of the development and functions of the placenta. For the obstetric clinician, being able to monitor the placenta throughout the pregnancy and to measure the impact of any treatment modality on the mother and the developing fetus are essential for providing the best possible care. The Eunice Kennedy Shriver National Institute of Child Health and Human Development at the National Institutes of Health has been a longtime supporter of research on the placenta. In 2014, the Human Placenta Project was initiated to help to drive an understanding of the biology of the human placenta and to facilitate the development of novel tools and approaches to allow for safe, noninvasive, real-time assessment of the placenta across pregnancy. Those efforts, along with others from around the globe, are showing promise. Although not yet ready for clinical application, these advances are moving the field forward and are certain to have a tremendous impact on the development and assessment of therapeutics designed for treating conditions of pregnancy.

Quantification of Wave Reflection in the Human Umbilical Artery From Asynchronous Doppler Ultrasound Measurements

Elevated umbilical artery pulsatility is a widely used biomarker for placental pathology leading to intra-uterine growth restriction and, in severe cases, still-birth. It has been hypothesized that placental pathology modifies umbilical artery pulsatility by altering the degree to which the pulse pressure wave, which originates from the fetal heart, is reflected from the placental vasculature to interfere with the incident wave. Here we present a method for estimating the reflected pulse wave in the umbilical artery of human fetuses using asynchronously acquired Doppler ultrasound measurements from the two ends of the umbilical cord. This approach assumes non-dispersive and loss-less propagation of the waves along the artery and models the reflection process as a linear system with a parameterized impulse response. Model parameters are determined from the measured Doppler waveforms by constrained optimization. Velocity waveforms were obtained from 142 pregnant volunteers where 123 met data quality criteria in at least one umbilical artery. The reflection model was consistent with the measured waveforms in 183 of 212 arteries that were analyzed. The analysis method was validated by applying it to simulated datasets and comparing solutions to ground-truth. With measurement noise levels typical of clinical ultrasound, parameters describing the reflected wave were accurately determined.

Effect of maternal betamethasone administration on feto-placental vascular resistance in the mouse†

Antenatal corticosteroids are often administered to women at risk of preterm birth to accelerate fetal lung development; however, there is evidence that this treatment may adversely affect placental function in some fetuses. Our group has recently demonstrated that wave reflections in the umbilical artery (UA), measured using high-frequency ultrasound, are sensitive to placental vascular abnormalities. In the present study, we used this approach to investigate the effect of maternal administration of betamethasone, a clinically relevant corticosteroid, on the feto-placental vasculature of the mouse. Fetuses were assessed at embryonic day (E)15.5 and E17.5 in C57BL6/J mice. At both gestational ages, the UA diameter, UA blood flow, and the wave reflection coefficient were significantly elevated in the betamethasone-treated mice compared to vehicle-treated controls. These observations support the interpretation that placental vascular resistance dropped with betamethasone treatment to an extent that could not be explained by vasodilation of the UA alone. Consistent with clinical studies, the effect of betamethasone on UA end-diastolic velocity was heterogeneous. Our results suggest that UA wave reflections are more sensitive to acute changes in placental vascular resistance compared with the UA pulsatility index, and this technique may have clinical application to identify a favorable placental vascular response to fetal therapies such as antenatal corticosteroids, where the fetal heart rate is likely to vary.

Periconceptional exposure to lopinavir, but not darunavir, impairs decidualization: a potential mechanism leading to poor birth outcomes in HIV-positive pregnancies

STUDY QUESTION

Does HIV protease inhibitor (PI)-based combination antiretroviral therapy (cART) initiated at periconception affect key events in early pregnancy, i.e. decidualization and spiral artery remodeling?

SUMMARY ANSWER

Two PIs, lopinavir and darunavir, currently offered as cART options in HIV-positive pregnancies were evaluated, and we found that lopinavir-based cART, but not darunavir-based cART, impaired uterine decidualization and spiral artery remodeling in both human ex vivo and mouse in vivo experimental models.

WHAT IS KNOWN ALREADY

Early initiation of cART is recommended for pregnant women living with HIV. However, poor birth outcomes are frequently observed in HIV-positive pregnancies exposed to PI-based cART, especially when it is initiated prior to conception. The correlation between early initiation of PI-cART and adverse birth outcomes is poorly understood, due to lack of data on the specific effects of PI-cART on the early stages of pregnancy involving uterine decidualization and spiral artery remodeling.

STUDY DESIGN, SIZE, DURATION

Lopinavir and darunavir were evaluated in clinically relevant combinations using an ex vivo human first-trimester placenta-decidua explant model, an in vitro human primary decidual cell culture system, and an in vivo mouse pregnancy model. The first-trimester (gestational age, 6–8 weeks) human placenta-decidua tissue was obtained from 11 to 15 healthy women undergoing elective termination of pregnancy. C57Bl/6 female mice (four/treatment group) were administered either lopinavir-cART, darunavir-cART or water by oral gavage once daily starting on the day of plug detection until sacrifice.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Human: Spiral artery remodeling was assessed by immunohistochemical analysis of first-trimester placenta-decidua explant co-culture system. Trophoblast migration was measured using a placental explant culture. A primary decidual cell culture was used to evaluate the viability of immune cell populations by flow cytometry. Soluble factors, including biomarkers of decidualization and angiogenesis, were quantified by ELISA and Luminex assay using decidua-conditioned media.

Mouse: In the mouse pregnancy model, gestational day 6.5 or 9.5 implantation sites were used to assess decidualization, spiral artery remodeling and uterine natural killer (uNK) cell numbers by immunohistochemistry. Transcription factor STAT3 was assayed by immunohistochemistry in both human decidua and mouse implantation sites.

MAIN RESULTS AND THE ROLE OF CHANCE

Lopinavir-cART, but not darunavir-cART, impaired uterine decidualization and spiral artery remodeling in both experimental models. Lopinavir-cART treatment was also associated with selective depletion of uNK cells, reduced trophoblast migration and defective placentation. The lopinavir-associated decidualization defects were attributed to a decrease in expression of transcription factor STAT3, known to regulate decidualization. Our results suggest that periconceptional initiation of lopinavir-cART, but not darunavir-cART, causes defective maturation of the uterine endometrium, leading to impairments in spiral artery remodeling and placentation, thus contributing to the poor birth outcomes.

LARGE SCALE DATA

N/A

LIMITATIONS, REASONS FOR CAUTION

The human first-trimester placenta/decidua samples could only be obtained from healthy females undergoing elective termination of pregnancy. As biopsy is the only way to obtain first-trimester decidua from pregnant women living with HIV on PI-cART, ethics approval and participant consent are difficult to obtain. Furthermore, our animal model is limited to the study of cART and does not include HIV. HIV infection is also associated with immune dysregulation, inflammation, alterations in angiogenic factors and complement activation, all of which could influence decidual and placental vascular remodeling and modify any cART effects.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings provide mechanistic insight with direct clinical implications, rationalizing why the highest adverse birth outcomes are reported in HIV-positive pregnancies exposed to lopinavir-cART from conception. We demonstrate that dysregulation of decidualization is the mechanism through which lopinavir-cART, but not darunavir-cART, use in early pregnancy leads to poor birth outcomes. Although lopinavir is no longer a first-line regimen in pregnancy, it remains an alternate regimen and is often the only PI available in low resource settings. Our results highlight the need for reconsidering current guidelines recommending lopinavir use in pregnancy and indicate that lopinavir should be avoided especially in the first trimester, whereas darunavir is safe to use and should be the preferred PI in pregnancy.

Further, in current times of the COVID-19 pandemic, lopinavir is among the top drug candidates which are being repurposed for inclusion in clinical trials world-over, to assess their therapeutic potential against the dangerous respiratory disease. Current trials are also testing the efficacy of lopinavir given prophylactically to protect health care workers and people with potential exposures. Given the current extraordinary numbers, these might include women with early pregnancies, who may or may not be cognizant of their gestational status. This is a matter of concern as it could mean that women with early pregnancies might be exposed to this drug, which can cause decidualization defects. Our findings provide evidence of safety concerns surrounding lopinavir use in pregnancy, that women of reproductive age considering participation in such trials should be made aware of, so they can make a fully informed decision.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by funding from the Canadian Institutes of Health Research (CIHR) (PJT-148684 and MOP-130398 to L.S.). C.D. received support from CIHR Foundation (FDN143262 to Stephen Lye). S.K. received a TGHRI postdoctoral fellowship. The authors declare that there are no conflicts of interest. L.S. reports personal fees from ViiV Healthcare for participation in a Women and Transgender Think Tank.

Ultra-High Frequency Ultrasound, A Promising Diagnostic Technique: Review of the Literature and Single-Center Experience

OBJECTIVES

Ultra-high frequency ultrasonography (UHFUS) is a recently introduced diagnostic technique which finds several applications in diverse clinical fields. The range of frequencies between 30 and 100 MHz allows for high spatial resolution imaging of superficial structures, making this technique suitable for the imaging of skin, blood vessels, musculoskeletal anatomy, oral mucosa, and small parts. However, the current clinical applications of UHFUS have never been analyzed in a consistent multidisciplinary manner. The aim of this study is to revise and discuss the current applications of UHFUS in different aspects of research and clinical practice, as well as to provide some examples of the current work-in-progress carried out in our center.

MATERIALS AND METHODS

A literature search was performed in order to retrieve articles reporting the applications of UHFUS both in research and in clinical settings. Inclusion criteria were the use of frequencies above 30 MHz and study design conducted in vivo on human subjects.

RESULTS

In total 66 articles were retrieved. The majority of the articles focused on dermatological and vascular applications, although musculoskeletal and intraoral applications are emerging fields of use. We also describe our experience in the use of UHFUS as a valuable diagnostic support in the fields of dermatology, rheumatology, oral medicine, and musculoskeletal anatomy.

CONCLUSION

Ultra-high frequency ultrasonography application involves an increasing number of medical fields. The high spatial resolution and the superb image quality achievable allow to foresee a wider use of this novel technique, which has the potential to bring innovation in diagnostic imaging.

CORP: Practical tools for improving experimental design and reporting of laboratory studies of cardiovascular physiology and metabolism

The exercise consisted of: 1) a short survey to acquire baseline data on current practices regarding the conduct of animal studies, 2) a series of presentations for promoting awareness and providing advice and practical tools for improving experimental design, and 3) a follow-up survey 12 mo later to assess whether practices had changed. The surveys were compulsory for responsible investigators (n = 16; paired data presented). Other investigators named on animal ethics applications were encouraged to participate (2017, total of 36 investigators; 2018, 37 investigators). The major findings to come from the exercise included 1) a willingness of investigators to make changes when provided with knowledge/tools and solutions that were relatively simple to implement (e.g., proportion of responsible investigators showing improved practices using a structured method for randomization was 0.44, 95% CI (0.19; 0.70), P = 0.003, and deidentifying drugs/interventions was 0.40, 95% CI (0.12; 0.68), P = 0.010); 2) resistance to change if this involved more personnel and time (e.g., as required for allocation concealment); and 3) evidence that changes to long-term practices ("habits") require time and follow-up. Improved practices could be verified based on changes in reporting within publications or documented evidence provided during laboratory visits. In summary, this exercise resulted in changed attitudes, practices, and reporting, but continued follow-up, monitoring, and incentives are required. Efforts to improve experimental rigor will reduce bias and will lead to findings with the greatest translational potential.NEW & NOTEWORTHY The goal of this exercise was to encourage preclinical researchers to improve the quality of their cardiac and metabolic animal studies by 1) increasing awareness of concerns, which can arise from suboptimal experimental designs; 2) providing knowledge, tools, and templates to overcome bias; and 3) conducting two short surveys over 12 mo to monitor change. Improved practices were identified for the uptake of structured methods for randomization, and de-identifying interventions/drugs.Listen to this article's corresponding podcast at https://ajpheart.podbean.com/e/experimental-design-survey-training-practical-tools/.

Reflected hemodynamic waves influence the pattern of Doppler ultrasound waveforms along the umbilical arteries

The pulsatile pattern of blood motion measured by Doppler ultrasound within the umbilical artery is known to contain useful diagnostic information and is widely used to monitor pregnancies at risk of fetal growth restriction or stillbirth. Animal studies have identified reflected pressure waves traveling counter to the direction of blood flow as an important factor in the shape of these waveforms. In the present study, we establish a method to measure reflected waves in the human umbilical artery and assess their influence on blood velocity pulsation. Ninety-five pregnant women were recruited from a general obstetrics clinic between 26 and 37 wk of gestation and examined by Doppler ultrasound. Blood velocity waveforms were recorded for each umbilical artery at three locations along the umbilical cord. With the use of a computational procedure, a pair of forward and reverse propagating waves was identified to explain the variation in observed Doppler ultrasound waveforms along the cord. Among the data sets that met data quality requirements, waveforms in 93 of the 130 arteries examined agreed with the wave reflection model to within 1.5% and showed reflections ranging in magnitude from 3 to 52% of the forward wave amplitude. Strong reflections were associated with large differences in pulsatility between the fetal and placental ends of the cord. As reflections arise from transitions in the biomechanical properties of blood vessels, these observations provide a plausible mechanism for the link between abnormal waveforms and clinically significant placental pathology and could lead to more precise screening methods for detecting pregnancies complicated by placental disease. NEW & NOTEWORTHY The pulsatile pattern of blood motion measured by Doppler ultrasound within the umbilical artery is known to contain useful diagnostic information and is widely used to monitor pregnancies at risk of fetal growth restriction. We demonstrate based on a study of 95 pregnant women that the shape of these umbilical artery waveforms is explained by the presence of a reflected pressure wave traveling counter to the direction of blood flow.