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

Abstract

ObjectiveThe objective of our study is to use Superb Micro‐Vascular Imaging® (SMI) to longitudinally evaluate spiral artery (SA) and uterine artery (UtA) vascular adaptation in normal human pregnancy, and to develop reference ranges for its use at various gestational ages throughout pregnancy.MethodsThe data for this study was obtained from a National Institute of Health (NIH) funded study on the Human Placenta Project (HD 086313‐01). Women aged 18‐35 years, with a body mass index (BMI) <30, without existing comorbidities, with a singleton gestation conceived spontaneously, and gestational age at or less than 13 6/7 weeks were eligible for inclusion. The current analysis was restricted to uncomplicated pregnancies carried through term. Exclusions included, maternal or neonatal complications, fetal or umbilical cord anomalies, abnormal placental implantation, or delivery <37 weeks. Women who fulfilled our inclusion criteria formed the reference population of our Human Placenta Project study. Each participant underwent 8 longitudinal ultrasound examinations during pregnancy. The pulsatility index (PI) of both the left and right UtA were obtained twice for each artery and the presence or absence of a notch was noted. Using Superb Micro‐Vascular Imaging® technology, the total number of spiral SA imaged was recorded in a sagittal placental section at the level of cord insertion. The PI and peak systolic velocity (PSV) were also measured in a total of 6 SA, including 2 in the central portion of the placenta, 2 peripherally towards the uterine fundal portion, and 2 peripherally towards the lower uterine segment of the placenta.Results90 women fulfilled our study criteria. Maternal UtA PI decreased throughout the first half of pregnancy from a mean of 1.39±0.50 at 12‐13 weeks gestation to 0.88±0.24 at 21‐22 weeks gestation. The mean number of SA visualized in a sagittal plane of the placenta increased from 8.83±2.37 in the first trimester to 16.99±3.31 in the late third trimester. The mean SA‐PI was 0.57±0.12 in the first trimester and progressively decreased during the second trimester, reaching a nadir of 0.4±0.1 at 24‐25 weeks and then remaining constant until the end of pregnancy. SA‐PSV was highest in early pregnancy with a mean of 57.16±14.84 cm/sec at 12‐13 weeks’ gestation, declined to a mean of 49.38±17.88 cm/sec at 20‐21 weeks’ gestation and continued to trend downward for the remainder of pregnancy reaching a nadir of 34.50±15.08 cm/sec at 36‐37 weeks’ gestation. A statistically significant correlation was noted between SA PI and UtA PI (r=0.5633, p<0.001). Multilevel regression models with natural cubic splines were used to create reference ranges of SA PSV and SA PI for given gestational ages.ConclusionWe have demonstrated the ability to image and quantify SA blood flow in normal pregnancies, starting from early gestation and developed reference ranges for use at various gestational ages throughout pregnancy.This article is protected by copyright. All rights reserved.