Fetal hyaloid artery in first trimester of pregnancy: slowflowHD study.

Objectives: To detect fetal hyaloid artery (FHA) blood flow using SlowflowHD in the first trimester.

Methods: During the 8-month period from February to September 2023, one-hundred and eighty-three trans-abdominal scans were performed for first-trimester screening in singleton pregnancies at 11-13 + 6 weeks of gestation. One-hundred and fifty-two cases were excluded from the study due to inappropriate fetal positions, excessive fetal movements, and excessive distances between the fetus and probe; thus, thirty-one fetuses (20.4 %) were examined, comprising 19 uni- and 12 bilateral orbits. One fetus with trisomy 21 was also evaluated at 12 weeks and 1 day. FHA was classified into two types based on the starting point angle (Straight, straightly diverged from ophthalmic artery; and Curved, crookedly diverged from ophthalmic artery) using SlowflowHD.

Results: In 19 uni- and 12 bilateral orbits in 31 fetuses, FHA could be identified in all orbits. In one orbit at 13 weeks and 5 days, blood flow on the string FHA could be detected. The vasa hyaloidea propria was noted in 3 orbits, and the posterior vascular capsule was depicted in 7 orbits. The incidence of Straight-type FHA increased with advancing gestation (p<0.0001). In a fetus with Trisomy 21, Straight-type FHA was noted in the left orbit, whereas FHA could not be identified in the right orbit.

Conclusions: This is the first report on the detection of FHA in the first trimester of pregnancy. SlowflowHD may be a useful diagnostic modality to evaluate human vascular development, such as FHA in utero.