[''Isolated'' single umbilical artery: incidence, cytogenetic abnormalities, malformation and perinatal outcome].

AIM: The aim of the study was to 1) evaluate the gestational age at diagnosis and the incidence of single umbilical artery in an unselected population of 3750 pregnant women; 2) identify its association with malformations and/or karyotype aberrations in pre/postnatal age; 3) evaluate the fetal-neonatal outcome; 4) investigate the likelihood that a fetus might be affected by a cytogenetic abnormality even in presence of an apparently ''isolated'' single umbilical artery.

METHODS: Transabdominal ultrasound of the umbilical vessels and histological confirmation at birth. In presence of single umbilical artery an accurate prenatal ultrasound assessment, karyotyping (pre/postnatal), and clinical follow-up after birth were performed.

RESULTS: The incidence of single umbilical artery in our population resulted 1.07% (40/3750), being ''isolated'' in 40% of cases. The diagnosis of chromosomal aberration associated with single umbilical artery was made in 6 cases (15%), while structural fetal abnormalities in absence of causal chromosomal anomalies were present in 9 cases (22.5%), with syndromic patterns in 3 of them. In 2 cases with chromosomal anomalies the single umbilical artery was apparently ''isolated'' at the ultrasound examination between the 17th and the 22nd week of gestation. Excluding 4 terminations of pregnancy, the perinatal mortality percentage resulted 25% (9/36); similarly, fetal growth retardation was present in 25% of cases (9/36).

CONCLUSIONS: The incidence of single umbilical artery in our population confirms that this fetal vascular anomaly is frequently identified in pregnancy. In the light of our cases and data in the literature it is evident that diligent surveillance in prenatal age and accurate clinical follow-up after birth are mandatory when a single umbilical artery has been diagnosed. Finally, the possibility, even if rare, that even when the single umbilical artery is apparently ''isolated'', a chromosomal aberration might be present (1/24 of our ''isolated'' cases) should be considered when addressing correct counselling to the couples.