Objective: Signs of increased uterine artery vascular impedance in mid-gestation are strongly related to pre-eclampsia later in pregnancy. Whether this is true for the late third trimester is, however, unclear. The aim of the present study was to analyze the frequency of increased uterine artery vascular impedance in the third trimester, and its relationship to abnormal umbilical artery Doppler and adverse outcome of pregnancy.
Methods: This was a retrospective study of uterine and umbilical artery Doppler velocimetry in 570 pregnancies complicated by pre-eclampsia. The managing clinician was informed only about the umbilical artery flow. The Doppler recordings were related to severity of pre-eclampsia, prematurity, fetal growth restriction, and rates of Cesarean section and admission to neonatal intensive care.
Results: Increased umbilical artery vascular impedance was seen in 59 cases (10.4%), seven having absent or reversed end-diastolic flow. Uterine artery notching was seen in 145 cases (25%), 88 (15%) having bilateral notches. Either increased uterine artery pulsatility index (PI) or notching, or both, were seen in 207 women (36.3%). In 108 women with severe pre-eclampsia, 38 (35.2%) had uterine artery notching. Signs of increased uteroplacental vascular impedance were more common in severe than in mild pre-eclampsia (57.4% vs. 31.4%), in premature than in term pregnancies (70.9% vs. 28.4%), and were more prevalent than abnormality in the umbilical artery (36.3% vs. 10.4%).
Conclusion: Only one-third of pre-eclamptic cases showed signs of increased uterine artery vascular impedance in the third trimester. However, signs of increased vascular impedance were much more frequent in the uterine than in the umbilical arteries and were strongly related to adverse outcome of pregnancy.