EP08.02: Growth follow‐up on fetuses with single umbilical artery or persistent right umbilical vein: is a 28–32‐week ultrasound needed?

Pregnancies found to have a single umbilical artery (SUA) or persistent right umbilical vein (PRUV) are associated with fetal anomalies. If targeted ultrasound and screening fetal ECHO finds otherwise normal anatomy, there is an increased risk of small for gestational age (SGA). The purpose of this study is to determine if current practice of recommending growth assessments between 28-32 detects (SGA) fetuses in this population. We conducted a retrospective review of 753 singleton pregnancies with SUA, and 44 with PRUV between January 2017- 2020, through the Calgary MFM Center. 466 SUA and 36 PRUV pregnancies were analysed. Pregnancies that were terminated due to anomalies, or those missing delivery/ultrasound surveillance data were excluded. The primary outcome was the rate of SGA fetuses. Secondary outcome was the detection rate of SGA at current recommended follow up ultrasound protocol. We found 19.1% (n = 89, 95% CI 15.6% to 22.7%) of all SUA pregnancies and 5.6% (n = 2, 95% CI 0.7% to 19.2) of PRUV pregnancies were SGA at time of delivery (baseline rate of SGA from unpublished local Calgary data of low risk pregnancies is 12%). Of SUA pregnancies that were SGA at delivery, 67.4% did not have SGA noted on ultrasound throughout the pregnancy, and SGA was first noted at time of delivery. Only 2.8% (95% CI 1.4% to 4.6%) of SUA pregnancies and 0% (95% CI 0.0% to 10.0%) of PRUV pregnancies were found to be SGA at 28-32wk ultrasound (the current local protocol for growth follow up of SUA and PRUV pregnancies). SUA and PRUV have known increased risk of SGA, our data shows that SUA confers a larger risk for SGA than PRUV. However, in analysis of ultrasound data from our centre, routine ultrasound at 28-32wk did not increase the detection of SGA in these pregnancies. We recommend that if there is no concern for SGA at the time of detailed ultrasound or fetal ECHO, then a 28-32wk ultrasound is not necessary and one ultrasound in the later third trimester is sufficient for monitoring in the absence of other clinical concerns.