Natural Course of Fetal Hyaloid Artery SlowflowHD Longitudinal Study

Objective To assess the natural course of the fetal hyaloid artery (FHA) using SlowflowHD during pregnancy. Methods One-hundred and eighteen normal fetuses were studied longitudinally using SlowflowHD to assess the natural course of FHA at 18-21 + 6, 28-31 + 6, and after 35 weeks of gestation. Blood flow of FHA with/without its branches (BF) was evaluated using SlowflowHD, and the band of FHA without blood flow (Band) was identified in each gestational period. The natural course of FHA was classified into six types: Type A, not detected (ND) in each gestational period; Type B, Band at 18-21 + 6 weeks; Type C, Band at 18-21 + 6 and 28-31 + 6 weeks; Type D, BF at 18-21 + 6 weeks; Type E, BF at 18-21 + 6 weeks and Band at 28-31 + 6 weeks; Type F, BF at 18-21 + 6 and 28-31 + 6 weeks. Results BF, Band, and ND were 83.5, 15.5, and 1.0% at 18-21 + 6 weeks, 8.8, 15.5, and 75.7% at 28-31 + 6 weeks, and 0, 0, and 100% after 35 weeks, respectively. Type A was 1.0%, Type B was 13.6%, Type C was 1.9%, Type D was 61.2%, Type E was 13.6%, and Type F was 8.7%. Conclusions The presence of FHA blood flow before 30 weeks of gestation should be regarded as a physiologic phenomenon in normal fetuses.