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Scalp Lead Placement


Internal cardiac monitoring with a scalp lead is used to identify fetuses at risk for serious complications from hypoxia during labor. Labor represents a unique stress on the fetus in utero. Uterine contractions reduce the flow of maternal blood to the placenta, in some cases uncovering a deficit in placental capacity. In addition, labor and the associated rupture of the chorioamnion may be associated with various other pregnancy risks, including intrauterine bacterial infection, umbilical cord compression, and placental abruption.

Recording the fetal heart rate in labor was developed in the 1960s as a means of assessing fetal status and documenting fetal well-being. Currently, 2 technologies are commonly available: an “external” monitor that uses Doppler technology to identify fetal heart motion via a sensor applied to the maternal abdomen and an “internal” monitor that directly records the fetal ECG via a single electrode applied to the fetal scalp (a fetal scalp electrode). Inherent differences are observed between the signal recordings via these 2 methods. The fetal scalp electrode detects actual beat-to-beat electrical signals of the fetal heart, whereas the external monitor uses an “averaging algorithm” to smooth the signal generated from the Doppler.

Regardless of the technology, the result is a recorded fetal heart rate. The fetal heart rate pattern is interpreted according to a standard set of criteria
with the goal being to identify fetuses at risk for serious complications during labor. The system remains imperfect, as a large number of fetuses display patterns that are neither clearly normal (category 1) or clearly abnormal (category 3). However, the ability to perform continuous fetal heart monitoring in labor is part of the standard of care for an obstetric unit in the United States.

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