Assessment of Fetal Growth on the Basis of Signal Strength in Fetal Magnetocardiography

Abstract

Fetal magnetocardiography has shown that fetal P wave and QRS complex durations increase with gestational age, reflecting change in cardiac muscle mass. The latter should, in principle, be associated with an increase in signal strength. We examined two approaches for determining QRS signal strength in a healthy fetus on a weekly basis in the second and third trimester. Twenty-two fetal magnetocardiograms of the same fetus were obtained using a 61 channel Magnes 1300 biomagnetometer (20th - 42nd week of gestation). In the signal averaged fetal beat produced at each week, signal strength was assessed on the basis of 1) peak-to-peak QRS signal amplitudes and 2) strength of an equivalent current dipole (ECD) computed at R peak. The results were assessed on the basis of correlation to week of gestation and by comparison to changes in QRS interval duration. All values increased with advancing gestation and regression analysis suggested a nonlinear dependency on age. ECD strength reflected gestational age slightly more reliably (r2=0.93) than signal amplitude values (mean, median, maximum: r2=089, 0.88, 0.85, respectively). ECD strength and mean signal amplitude also correlated well (r=0.97, p