B‐flow/spatiotemporal image correlation M‐mode: novel ultrasound method that detects decrease in spiral artery luminal diameter in first trimester in primate model of impaired spiral artery remodeling

OBJECTIVE: To determine if B‐flow/spatiotemporal image correlation (STIC) M‐mode ultrasonography detects a decrease in spiral artery luminal diameter and volume flow during the first trimester in a non‐human primate model of impaired spiral artery remodeling (SAR). METHODS: Pregnant baboons were treated daily with estradiol benzoate on days 25–59 of the first trimester (term, 184 days), or remained untreated. On day 60 of gestation, spiral artery luminal diameter (in seven untreated and 12 estradiol‐treated baboons) and volume flow (in four untreated and eight estradiol‐treated baboons) were quantified by B‐flow/STIC M‐mode ultrasonography. In addition, in 15 untreated and 18 estradiol‐treated baboons, the percent of spiral arteries remodeled by extravillous trophoblasts was quantified ex vivo by immunohistochemical image analysis on placental basal plate tissue collected via Cesarean section on day 60. Findings were compared between treated and untreated animals. The correlation between spiral artery luminal diameter and percent of SAR was assessed in three untreated and six estradiol‐treated baboons which underwent both B‐flow/STIC M‐mode ultrasound and quantification of SAR. RESULTS: The proportion of spiral arteries greater than 50 µm in diameter remodeled by extravillous trophoblasts was 70% lower in estradiol‐treated baboons than in untreated animals (P = 0.000001). Spiral artery luminal diameter in systole and diastole, as quantified by B‐flow/STIC M‐mode in the first trimester of pregnancy, was 31% (P = 0.014) and 50% (P = 0.005) lower, respectively, and volume flow was 85% lower (P = 0.014), in SAR‐suppressed baboons compared with untreated animals. There was a significant correlation between spiral artery luminal diameter as quantified by B‐flow/STIC M‐mode ultrasonography and the percent of SAR (P < 0.05). CONCLUSION: B‐flow/STIC M‐mode ultrasonography provides a novel real‐time non‐invasive method to detect a decrease in uterine spiral artery luminal diameter and volume flow during the cardiac cycle, reflecting decreased distensibility of the vessel wall, in the first trimester in a non‐human primate model of defective SAR. © 2021 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.