Changes in the conduction of the fetal electrocardiogram to the maternal abdominal surface during gestation.

A technique for recording high-quality vectorcardiograms from the fetus in utero is described. A study was conducted to clarify conflicting views on the mechanism of fetal electrocardiogram (FECG) signal transmission to the maternal abdominal surface during the latter half of gestation. The results of this study support the view that a general pattern of uniform conduction of FECG currents exists between 20 and 28 weeks' gestation in most subjects, that signal magnitudes decrease markedly between 28 and 34 weeks' gestation and conduction tends to behave as if it is nonuniform through the maternal abdominal volume, and that a preferred signal pathway, possibly through the oronasal cavities of the fetus, appears to develop after 34 weeks' gestation and continues until term. Two different abdominal FECG lead systems are recommended on the basis of these findings which should maximize the accuracy of FECG monitoring of the preterm fetus.