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.

Keywords: Adaptation; Doppler; Pregnancy; Remodeling; Spiral artery.

Fig. 1

PRISMA 2009 flow diagram. N = amount of articles

Fig. 2

Forest plot of studies exploring spiral artery measurements (Pulsatility Index) during first, second and third trimester in healthy pregnancies

Fig. 3

Meta-regression curve of spiral artery measurements (Pulsatility Index) during first, second and third trimester in healthy pregnancies. Every color is representing one article, except for Matijevic et al. (ref. [9]) and Hsieh et al. (ref. [23]) who have two colors representing central and peripheral located spiral artery measurements. ‘N’ represents the maximum amount of cases included in the study, shown as a small or larger circle

Fig. 4

Forest plot of studies exploring spiral artery measurements (Resistance Index) during first, second and third trimester in healthy pregnancies

Fig. 5

Meta-regression curve of spiral artery measurements (Resistance Index) during first, second and third trimester in healthy pregnancies. Every color is representing one article, except for Matijevic et al. (ref. [9]) and Hsieh et al. (ref. [23]) who have two colors representing central and peripheral located spiral artery measurements. ‘N’ represents the maximum amount of cases included in the study, shown as a small or larger circle

Fig. 6

Forest plot of studies exploring spiral artery measurements (Peak Systolic Velocity m/s) during first, second and third trimester in healthy pregnancies

Fig. 7

Meta-regression curve of spiral artery measurements (Peak Systolic Velocity) during first, second and third trimester in healthy pregnancies. Every color is representing one article, except for Hsieh et al. (ref. [23]) who have two colors representing central and peripheral located spiral artery measurements. ‘N’ represents the maximum amount of cases included in the study, shown as a small or larger circle

Fig. 8

Forest plot of 2 studies exploring spiral artery measurements (Pulsatility Index) during first trimester in complicated pregnancies

Fig. 9

Forest plot of 2 studies exploring both central and peripheral spiral artery measurements during second trimester (Pulsatility Index)

Fig. 10

Forest plot of 2 studies exploring both central and peripheral spiral artery measurements during second trimester (Resistance Index)