ST segment analysis as an adjunct to electronic fetal monitoring, Part I: background, physiology, and interpretation.

Fetal electrocardiogram (ECG) ST segment analysis (STAN) was approved in 2005 in the United States as an adjunct to electronic fetal heart rate monitoring to determine whether obstetrical intervention is warranted when there is an increased risk for developing metabolic acidosis. STAN has utility in the reduction of fetal acidosis at birth, decreased need for fetal scalp blood sampling during labor, and decreased need for operative vaginal delivery and emergency cesarean delivery for fetal indications. This article discusses specific fetal ECG changes and their significance and the use of the STAN system.