Measurement of compliance of the maternal abdominal wall in pregnancy.

Recent importance in the signal-to-noise ratio of fetal phonocardiograms has been attributed to a 'compliance-matching' between the phono-sensor and the maternal abdominal wall. We have developed a device to measure objectively the compliance of the maternal abdominal wall in pregnancy. Using this we have shown that the compliance varies considerably from patient to patient and that it varies most significantly (and inversely) with gestational age. As a result of this study we are now in a better position to optimize the compliance-matching of phono-sensors and thereby to detect fetal heart sounds with much more fidelity than hitherto.