Magnetomyographic assessment of pelvic floor muscles compared to ultrasound during pregnancy

Maternal birth injury contributes to future pelvic floor disorders, yet we possess an incomplete understanding of the levator ani muscles during pregnancy. We applied a noninvasive magnetomyography technique to characterize levator ani muscle activity in pregnancy with ultrasound and clinical exam. Magnetomyographic measures of levator ani muscle activity were collected using a noninvasive biomagnetic sensor from 53 pregnant women during rest and voluntary muscle contractions of varying intensity. Power spectral density was calculated using Welch's method to obtain the mean power of each Kegel exercise. Levator hiatus circumference was measured using ultrasound, and contraction strength was measured via the Brink scale. Magnetomyography data revealed a mean root mean square (RMS) rest of 39.7 ± 8.6 femtoTesla (fT) and Kegel of 52.9 ± 17.1 fT. Mean power spectral density (PSD) in log₁₀ (fT²/Hz) was 0.9 ± 0.2 at rest and 1.1 ± 0.2 during Kegel. Ultrasound measures of levator hiatus circumference were 13.3 ± 1.6 cm at rest and 11.6 ± 1.7 cm during maximum Kegel. Magnetomyographic correlations with levator hiatus circumference were stronger for amplitude and PSD at rest (-0.35 and -0.33) than for Kegel (-0.20 and -0.19). Magnetomyography-based amplitudes of pelvic floor activity directly correlate with ultrasound levator hiatus circumference during rest and Kegel.