Prenatal ultrasound diagnosis of single umbilical artery (SUA) and pregnancy outcomes

Dr YP Gounden, Senior Lecturer in Obstetrics and Gynaecology, University of Queensland, School of Medicine, Rural Clinical Division, Bundaberg Base Hospital, Bundaberg, Queensland

INTRODUCTION
The normal umbilical cord consists of two umbilical arteries and one umbilical vein surrounded by Wharton’s jelly. A single umbilical artery (SUA) has an incidence of 0.5%1 with a higher prevalence in twin pregnancies2. The aetiology remains unknown but the most likely mechanism is atrophy of the second umbilical artery during development.3,4
The clinical implications of SUA include an increased incidence of congenital and karyotype abnormalities, intrauterine growth restriction, premature birth and fetal death. Interpretation of Doppler velocimetry is problematic as estimates of normal values are based on the presence of two umbilical arteries. Patient counselling in the setting of SUA is required, especially with respect to fetal karyotyping.
The reported sensitivity and positive predictive value of sonographically detected SUA is 65%5. It is noted that two and three vessels can co-exist in different segments of the same umbilical cord6.
This paper reports the findings in five patients seen at a regional Queensland Base Hospital over twelve months with a prenatal ultrasound diagnosis of single umbilical artery.