Hypotension following spinal anesthesia in obstetric patients is commonplace. Spinal anesthesia induces a sympathectomy, leading to vasodilation, increased venous capacitance, and decreased venous return. High levels of sympathetic blockade can decrease maternal cardiac output although with lesser height and degrees of sympathetic blockade a compensatory increase in cardiac output may be seen secondary to reductions in cardiac afterload. Risk factors associated with spinal-induced hypotension include: increasing age, pre-existing hypertension, higher infant birth weight and obesity. Many studies have been carried out to determine the role of ephedrine and phenylephrine during spinal anesthesia for cesarean section. Chronic hypotension, especially if accompanied by decreased cardiac output, may reduce placental perfusion and impair fetal oxygenation. Drawbacks to ephedrine include variable efficacy at prophylaxis of hypotension secondary to spinal anesthesia in low doses or in doses normally used in the clinical setting.

Electronic fetal monitoring (EFM) primary screening test is a highly sensitive test detecting a disease with a low prevalence. The fetal heart rate (FHR) trace or cardiotocograph (CTG) has five recognisable features: uterine activity, baseline FHR, baseline variability, accelerations and decelerations. The National Institute for Health and Clinical Excellence guidelines on EFM recommend that a CTG or FHR trace is classified into one of three groups: normal, suspicious or pathological based on the presence of reassuring and non-reassuring features. Fetal blood sampling (FBS) is used to identify compromised fetuses that need immediate delivery from those that are fine. There is a need for a monitoring system with a high specificity and sensitivity for detecting fetal acidosis and allowing timely and appropriate intervention without putting the fetus at risk. Currently, systems being researched include fetal ECG analysis and fetal oxygen saturation monitoring.