OP05.04: Longitudinal reference range for the pulsatility index of fetal inferior adrenal arteries

Fetal growth restriction significantly impacts perinatal outcomes, with current monitoring strategies often failing to predict optimal delivery timing. Animal studies suggest the fetal adrenal glands, experiencing notable increases in blood flow during placental insufficiency, could be key for better monitoring. To investigate this potential in humans, we aimed to establish longitudinal pulsatility index (PI) reference ranges for the inferior adrenal artery using a newly developed ultrasound technique for identifying and measuring blood flow velocities in these vessels. The study was carried out at Stavanger University Hospital from June 2020 to May 2023. We enrolled 150 participants with low-risk singleton pregnancies, conducting sonographic examinations every 4-6 weeks from 19 weeks gestation until delivery. Pregnancies complicated by risk factors for fetal growth restriction were excluded. We used SlowFlow™ power Doppler to visualise the artery and pulsed wave Doppler to measure blood flow velocities. The PI was calculated to establish longitudinal reference ranges for gestational ages 190-410 by means of quantile regression allowing for repeated observations. 145 participants yielded in total 605 examinations where of 66 were without any valid measurements. Our study has established longitudinal reference ranges for the fetal inferior adrenal artery PI in a low-risk population, a possible tool for improved monitoring of fetal growth restriction. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.