Abstract
BackgroundDownstream remodeling of the spiral arteries (SpA) decreases utero-placental resistance drastically, allowing sustained and increased blood flow to the placenta under all circumstances. We systematically evaluated available reports to visualize adaptation of spiral arteries throughout pregnancy by ultra-sonographic measurements and evaluated when this process is completed.MethodsA systematic review and meta-analysis of spiral artery flow (pulsatility index (PI), resistance index (RI) and peak systolic velocity (PSV)) was performed. English written articles were obtained from Pubmed, EMBASE and Cochrane Library and included articles were assessed on quality and risk of bias. Weighted means of Doppler indices were calculated using a random-effects model.ResultsIn healthy pregnancies, PI and RI decreased from 0.80 (95% CI: 0.70–0.89) and 0.50 (95% CI: 0.47–0.54) in the first trimester to 0.50 (95% CI: 0.45–0.55, p < 0.001) and 0.39 (95% CI: 0.37–0.42, p < 0.001) in the second trimester and to 0.49 (95% CI: 0.44–0.53, p = 0.752) and 0.36 (95% CI: 0.35–0.38, p = 0.037) in the third trimester, respectively. In parallel, PSV altered from 0.22 m/s (95% CI: 0.13–0.30 m/s) to 0.28 m/s (95% CI: 0.17–0.40 m/s, p = 0.377) and to 0.25 m/s (95% CI: 0.20–0.30 m/s, p = 0.560) in the three trimesters. In absence of second and third trimester Doppler data in complicated gestation, only a difference in PI was observed between complicated and healthy pregnancies during the first trimester (1.49 vs 0.80, p < 0.001). Although individual studies have identified differences in PI between SpA located in the central part of the placental bed versus those located at its periphery, this meta-analysis could not confirm this (p = 0.349).ConclusionsThis review and meta-analysis concludes that an observed decrease of SpA PI and RI from the first towards the second trimester parallels the physiological trophoblast invasion converting SpA during early gestation, a process completed in the midst of the second trimester. Higher PI was found in SpA of complicated pregnancies compared to healthy pregnancies, possibly reflecting suboptimal utero-placental circulation. Longitudinal studies examining comprehensively the predictive value of spiral artery Doppler for complicated pregnancies are yet to be carried out.
Highlights
Downstream remodeling of the spiral arteries (SpA) decreases utero-placental resistance drastically, allowing sustained and increased blood flow to the placenta under all circumstances
Spiral arteries located in the central part of the placental bed, versus those located at its periphery Differences between central and peripheral SpA Doppler indices during the second trimester were investigated in two studies [9, 23]
Despite the fact that upstream uterine measurements are closely related to downstream SpA measurements [22], it is assumable that measuring resistance downstream could reflect the pathological process underlying placenta insufficiency related diseases in a superior practice
Summary
Downstream remodeling of the spiral arteries (SpA) decreases utero-placental resistance drastically, allowing sustained and increased blood flow to the placenta under all circumstances. At 12–13 weeks of gestation, trophoblast cells have invaded the decidual segments of maternal spiral arteries (SpA) and transformed these small, adrenergicsensitive high-resistance vessels into wide, adrenergicinsensitive low-resistance vessels [1, 2]. From 15 weeks onwards, a second, endovascular invasion starts to remodel the myometrial segments and is fully completed at mid-pregnancy [3]. Downstream remodeling of the SpA decreases utero-placental resistance drastically and allows significant increase in volumetric blood flow to the placenta [1, 4,5,6,7]. Inadequate remodeling of SpA in PS-pregnancies potentially affects the development of the placenta as high velocity blood flow could cause mechanical stress on the tissue, or could influence development due to perfusion-reperfusion injury [6, 7, 10]
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