Differences in perinatal outcomes according to forming period of single umbilical cord in singleton pregnancy

Objectives: The aim of this study was to establish the frequency and associations of single umbilical artery (SUA) diagnosed until the first vs second or third trimester. Methods: A retrospective cohort study was conducted on singleton pregnancies at a tertiary perinatal center. All women underwent both the first and second trimester scans in which the number of arteries in the umbilical cord was routinely documented. SUA was classified as aplastic type when the diagnosis was made in the first trimester and as occlusion type when diagnosed in the second or third trimester. Adverse perinatal outcome was calculated as occurrence of fetal death, birthweight centile < 10^th, or Apgar score at 5 minutes < 7. Results: A total of 8675 women underwent ultrasound examinations during the study period. Of the 32 SUA cases, 17 (0.2%) were of the aplastic type and 15 (0.2%) of the occlusion type. Congenital anomalies were more in aplastic than in occlusive SUA (58.8% vs 20%,.043). The occlusive SUA had higher postnatal coiling index (0.3 vs 0.2,.034) and diagnosis of hypercoiled cord (46.7% vs 5.9%,.013) than the aplastic type. Conclusions: The different gestational age at diagnosis and coiling characteristics suggest two types of SUA, namely, aplastic and occlusion types, which are associated with differences in perinatal outcomes.