Investigating the Novel Observation of Right-left Difference in Uterine Artery Vascular Resistance in Pre-eclampsia

Inclusion Criteria: * Pre-eclampsia patients and normal pregnancy controls scheduled to receive epidural catheterization for induction of labor or Cesarean delivery. Non-pregnant controls receiving epidural catheterization for elective surgery. Pre-eclampsia group: 1. gestational age between 35 to 40 completed weeks 2. uterine artery notching OR evidence of reduced uterine artery blood flow 3. resting systolic pressure \> 140mmHg or diastolic pressure \> 90mmHg measured twice at least 6 hours apart 4. proteinuria (at least 0•1 g/l in two random samples at least 6 hours apart or at least 0•3g in a 24 hour collection). * Normal pregnancy control group: 1. gestational age between 35 to 40 completed weeks 2. absence of other inclusion factors for the pre-eclampsia group. Non-pregnant control group: Non-pregnant women of reproductive age. Exclusion Criteria: * Active labor, resting blood pressure ≥ 160/110 (recorded on at least two occasions 6 hours apart), coagulopathy or other contraindications for epidural catheterization, abnormal fetal heart tracing, known fetal anomaly, intrauterine infection, placental anomalies, twins, and refusal of consent.