Fetal hyaloid artery in first trimester of pregnancy: slowflowHD study

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

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.

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.

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.