Risk of adverse pregnancy outcome in isolated single umbilical artery diagnosed at the mid-trimester anomaly scan: a large Danish retrospective cohort study

To examine the association of isolated single umbilical artery (iSUA) confirmed at the mid-trimester anomaly scan and adverse pregnancy outcome and congenital malformations with up to 10 years postnatal follow up. This retrospective cohort study included 116,501 singleton pregnancies consecutively enrolled in first trimester screening for aneuploidies and mid-trimester anomaly scan at three University Hospitals in the Capital Region of Copenhagen, Denmark. Data from the Danish Fetal Medicine Database (2008–2017) were verified by manually scrutinizing pre- and postnatal records. The main outcomes of interest were intrauterine fetal demise (IUFD), small for gestational age (SGA), preterm delivery, cesarean section and unrecognized pre- and postnatal congenital malformations. In total, 775 pregnancies with iSUA were identified. Isolated SUA were associated with a significantly increased risk of IUFD (OR 4.16, 95% CI 2.06–8.44), SGA < 3^rd centile (aOR 2.41, 95% 1.85–3.14) and SGA < 10^th centile (aOR 1.84, 95% CI 1.53–2.21), but not with preterm delivery or cesarean section. The laterality of the missing artery was not associated with SGA. In total, 4.3% of pregnancies with iSUA had unrecognized congenital malformations. 1.5% with iSUA had congenital cardiovascular malformations, which were considered minor. Isolated SUA is associated with IUFD and SGA, supporting surveillance during third trimester. If, during the mid-trimester scan, the sonographer achieves thorough, extended cardiac views and finds no additional malformation other than SUA, fetal echocardiography seems not to be needed.