Intra-placental arterial Doppler: A marker of fetoplacental vascularity in late-onset placental disease?

Inter- and intra-observer reliability in first-trimester uterine artery Doppler measurements

OBJECTIVES

This study aimed to evaluate the inter- and intra-observer reliability of Doppler ultrasound measurements of the uterine artery (UtA) pulsatility index (PI) in the first trimester of pregnancy. Doppler measurement of the UtA is an integral component in algorithms for calculating risks for developing conditions like pre-eclampsia and fetal growth restriction and for deciding which women should be given low-dose aspirin.

METHODS

This was a prospective observational cross-sectional study, enrolling low-risk singleton pregnant women between 11 + 0 and 13 + 6 weeks of gestation. Two sonographers alternated in performing three sets of transabdominal Doppler measurements of both right and left UtA. The study employed the True Reproducibility of Ultrasound Technique (TRUST) criteria to assess consistency of measurements. Statistical analysis involved calculating intra- and interobserver reliability and the proportion of measurements above the 95th percentile. Sensitivity analyses considered probe type and BMI.

RESULTS

A total of 58 pregnant women were included, resulting in 689 UtA Doppler measurements. Approximately 7.7% of these measurements exceeded the 95th percentile corrected for gestational age. Intra-observer reliability showed poor to moderate intra-class correlation (ICC) values. Interobserver reliability showed poor ICC values for the left and right UtA solely, and a moderate ICC for the average of the left and right UtA taken together. There was moderate to very good agreement between observers for measurements exceeding the 95th percentile. Sensitivity analyses revealed consistent results for probe type, but showed inverse correlation between BMI and the ICC of Doppler measurements.

CONCLUSION

The study showed at best a moderate reliability of first trimester transabdominal Doppler PI measurements of the uterine artery, according to TRUST criteria, and were negatively influenced by higher BMI. Continued research and innovation combined with regular training programs can enhance the reliability of both uterine Doppler and biochemical markers, ultimately further improving their clinical utility.

Fetal Tibial Artery Doppler in Late IUGR Fetuses: A Longitudinal Study

INTRODUCTION

Late-onset intrauterine fetal growth restriction (IUGR) is a common pregnancy complication diagnosed in 5-10% of pregnant women worldwide. Under the impact of hypoxia, the fetus develops a protective mechanism of adaptive changes occurring in the cerebral circulation ("brain-sparing effect").

MATERIALS AND METHODS

We conducted detailed longitudinal Doppler examinations and the monitoring of the fetal condition in 53 IUGR fetuses. Doppler measurements of the pulsatility index in the fetal tibial (TA-PI), umbilical (UA-PI), and middle cerebral arteries (MCA-PI) were performed, and the cerebral placental ratio (CPR) was determined on a weekly basis from the 33rd week to the birth.

RESULTS

The longitudinal analysis showed a significant increase in the TA-PI. The UA showed a plateau, but no increase was detected near term. The MCA-PI and CPR showed a progressive decrease in values from inclusion to delivery. Our findings indicate that the increase in the TA-PI was the first sign of the aggravating state of the fetus with the changes registered from the 35th week. The parameters of the UA-PI did not show significant changes, while the MCA and CPR became abnormal later from the 37th week.

CONCLUSIONS

These observations can serve towards the development of guidelines for detecting the deteriorating signs and intervention timing in IUGR during late pregnancies.

Doppler evaluation of normal and abnormal placenta

Doppler techniques are needed for the evaluation of the intraplacental circulation and can be of great value in the diagnosis of placental anomalies. Highly sensitive Doppler techniques can differentiate between the maternal (spiral arteries) and fetal (intraplacental branches of the umbilical artery) components of the placental circulation and assist in the evaluation of the placental functional units. A reduced number of placental functional units can be associated with obstetric complications, such as fetal growth restriction. Doppler techniques can also provide information on decidual vessels and blood movement. Abnormal decidual circulation increases the risk of placenta accreta. Doppler evaluation of the placenta greatly contributes to the diagnosis and clinical management of placenta accreta, vasa previa, placental infarcts, placental infarction hematoma, maternal floor infarction, massive perivillous fibrin deposition and placental tumors. However, it has a limited role in the diagnosis and clinical management of placental abruption, placental hematomas, placental mesenchymal dysplasia and mapping of placental anastomoses in monochorionic twin pregnancies. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Doppler Ultrasonography of the Fetal Tibial Artery in High-Risk Pregnancy and Its Value in Predicting and Monitoring Fetal Hypoxia in IUGR Fetuses

Background and Objectives: Intrauterine growth restriction (IUGR) is the term used to describe a fetus whose estimated weight is less than the 10th percentile of its age growth curve. IUGR is the second most common cause of perinatal death. In many cases there is a deficiency in the standardization of optimal management, prenatal follow-up and timing of delivery. Doppler examination is the most sensitive test that can assess the condition of the fetus and indicate fetal intrauterine hypoxia. Numerous studies of the fetal intrauterine state focus on the umbilical artery and the fetal cerebral blood vessels, while the peripheral arteries have so far received insufficient attention. Materials and Methods: We present a case of an IUGR fetus monitored with a non-stress test (NST) and a Doppler examination of the fetal arteries (tibial, umbilical, middle cerebral and uterine) and the ductus venosus. In this case the first early sign of fetal hypoxia was revealed by blood flow changes in the tibial artery. Results: We hypothesize that peripheral vascular changes (in the tibial artery) may more accurately reflect the onset of deterioration in the condition of the IUGR fetus, such that peripheral blood flow monitoring ought to be employed along with other techniques already in use. Conclusion: This paper describes the clinical presentation of an early detection of late IUGR hypoxia and claims that blood flow changes in the tibial artery signal the worsening of the fetus’s condition.

Pulsatility effects of flow on vascular tone in the fetoplacental circulation

INTRODUCTION

The regulation of vascular tone in the fetoplacental circulation is governed by endocrine and mechanical forces yielding a relaxed basal state in normal pregnancy. Flow mediated vasodilation, induced by shear stress and endothelial nitric oxide signalling, is key to driving vasorelaxation in this circulation. The pulsatile property of blood flow, as opposed to the flow rate, could provide an additional factor in this regulation, but its effects and signalling have never been explored in the fetoplacental microvasculature.

METHODS

Here, we studied the effects of non-pulsatile and pulsatile flow modalities on vascular resistance in the fetoplacental microcirculation of the human placenta using an ex vivo perfusion model; and examined a potential role for nitric oxide. We also explored whether the placental Doppler velocimetry waveform is sustained within subchorial arteries in vivo.

RESULTS

Pulsatile flow reduced basal impedance to flow during steady state perfusion compared to non-pulsatile flow, signalled through enhanced nitric oxide production. Doppler velocimetry waveforms were visible within the subchorial arteries in vivo.

CONCLUSION

This work suggests that the pulsatile property of flow through the fetoplacental circulation is sensed by the fetoplacental vasculature to mediate a signalling response and provide additional vasodilation of this microcirculation. We speculate that in pregnancy disease, altered amplitude and frequency of the subchorial pulse might impact on vascular function in a compromised high-resistance placental microcirculation.