Electrohysterography of labor contractions: propagation velocity and direction.

OBJECTIVE

Electrohysterographic assessment of the propagation velocity of uterine depolarization has been introduced as a promising predictor of preterm labor. Therefore, the objectives of this study were to characterize the uterine electrohysterographic signals during labor and to determine the propagation velocity and propagation direction of electrohysterographic signals.

DESIGN

Descriptive study.

SETTING

Department of Obstetrics and Gynecology, Aarhus University Hospital, Denmark.

POPULATION

Eight women in active labor at term.

METHODS

Electrohysterograms (three channels) were recorded using surface electrodes placed abdominally along the vertical median axis with an inter-electrode distance of 6.5-11.2 cm. In total, 89 contractions were analyzed.

RESULTS

Electrohysterographic characteristics: The duration of the contractions was 61.0 ± 18.0 s (mean ± SD). The median frequency of the power spectrum density was 0.51 (0.44; 0.51) Hz (median; 10th; 90th percentile). The greatest signal magnitude was obtained by the electrode in the centermost position. The propagation velocity: 2.15 (0.66; 13.8) cm/s in the upper part and 1.53 (0.58; 6.7) cm/s in the lower part of the uterus. Propagation direction: Both downward (58%) and upward (42%) propagation of the electrohysterographic signals occurred. Moreover, downward and upward propagations were recorded simultaneously in the upper and lower part of the uterus, suggesting a multidirectional propagation pattern.

CONCLUSIONS

Labor contractions, expressed by electrohysterographic signals, propagate both in the downward and upward direction, a phenomenon that must be taken into account when determining the propagation velocity for preterm labor diagnostics.