Spiral artery blood flow during pregnancy: a systematic review and meta-analysis

Abstract

Background Downstream 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. Methods A 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. Results In 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). Conclusions This 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.

Longitudinal assessment of spiral and uterine arteries in normal pregnancy using novel ultrasound tool

“…This study demonstrates that SA-PI and -PSV measurements are largely unaffected by SA sample location, as we assessed SA-PI and -PSV in three placental segments and documented no significant change overall with the exception of a single gestational window, which is most probably a statistical variation, rather than a physiologic change. Our finding is consistent with a 2020 meta-analysis examining SA blood flow during pregnancy which found no difference in SA-PI by SA location 24 . Interrogating the SA in the central portion of the placenta is therefore recommended, as it is commonly its thickest portion and thus easier technically.…”

Longitudinal assessment of spiral artery and intravillous arteriole blood flow and adverse pregnancy outcome

“…We also found that the mean RI values for both SA and IVA were significantly higher in the FGR group in the third trimester compared with pregnancies that did not develop FGR. The fall in SA resistance with gestational age is consistent with the observations of a recent meta-analysis which suggested that the reduction in SA-RI parallels the physiologic trophoblast invasion occurring particularly in the mid-trimester 32 . The increasing IVA resistance with increasing gestational age is difficult to explain physiologically, as we would expect this to mirror changes in the umbilical artery.…”

Doppler evaluation of normal and abnormal placenta

“…Spiral artery PI has been shown to be higher in the first and second trimesters among pregnant women who developed complications (i.e. hypertensive disorders, fetal growth restriction, preterm labor, placental abruption) as compared with uncomplicated pregnancies (1.49 vs 0.80; P < 0.001) 7 . The movement of maternal blood within the placenta has been tracked using ultrasound contrast in 25 pregnant women 9 .…”

“…The distance between jets increases near the periphery of the placenta and in obstetric complications, such as a small-for-gestational-age fetus and pre-eclampsia 6 . Doppler velocimetry studies of the spiral arteries show a reduction in the pulsatility index (PI) from 0.8 in the first trimester to 0.5 in the second and third trimesters 7 and a similar reduction in the resistance index (first trimester, 0.34; second trimester, 0.28; third trimester, 0.27) (Figure 2) 8 , with no changes in peak systolic velocity (PSV) (first trimester, 0.22 m/s; second trimester, 0.28 m/s; third trimester, 0.25 m/s; P = 0.56) 7 . Spiral artery PI has been shown to be higher in the first and second trimesters among pregnant women who developed complications (i.e.…”