Clinical meaning
Electronic fetal monitoring (EFM) is the continuous recording of the fetal heart rate (FHR) in relation to uterine contractions. The fetal heart rate is regulated by the autonomic nervous system through the interplay of the sympathetic and parasympathetic (vagal) divisions. The sympathetic nervous system increases heart rate and contractility, while the parasympathetic system, primarily via the vagus nerve (cranial nerve X), slows the heart rate. In a healthy, well-oxygenated fetus, these two systems create a balance that produces a baseline FHR between 110 and 160 beats per minute with moderate variability. Fetal oxygenation depends entirely on the uteroplacental circulation. Maternal blood enters the intervillous space of the placenta through the spiral arteries of the uterus. Oxygen and nutrients diffuse across the placental membrane into the fetal blood within the chorionic villi, while carbon dioxide and metabolic waste move in the opposite direction. Any condition that reduces maternal blood flow to the placenta (such as maternal hypotension, uterine tachysystole, or placental abruption) or impairs gas exchange at the placental membrane (such as placental insufficiency or infarction) will decrease fetal oxygenation. When...