Contraction of the levator ani muscle during Valsalva maneuver (coactivation) is associated with a longer active second stage of labor in nulliparous women undergoing induction of labor

Abstract

BACKGROUND: The Valsalva maneuver is normally accompanied by relaxation of the levator ani muscle, which stretches around the presenting part, but in some women the maneuver is accompanied by levator ani muscle contraction, which is referred to as levator ani muscle coactivation. The effect of such coactivation on labor outcome in women undergoing induction of labor has not been previously assessed. OBJECTIVE: The aim of the study was to assess the effect of levator ani muscle coactivation on labor outcome, in particular on the duration of the second and active second stage of labor, in nulliparous women undergoing induction of labor. STUDY DESIGN: Transperineal ultrasound was used to measure the anteroposterior diameter of the levator hiatus, both at rest and at maximum Valsalva maneuver, in a group of nulliparous women undergoing induction of labor in 2 tertiary-level university hospitals. The correlation between anteroposterior diameter of the levator hiatus values and levator ani muscle coactivation with the mode of delivery and various labor durations was assessed. RESULTS: In total, 138 women were included in the analysis. Larger anteroposterior diameter of the levator hiatus at Valsalva was associated with a shorter second stage (r ¼ e0.230, P ¼ .021) and active second stage (r ¼ e0.338, P ¼ .001) of labor. Women with levator ani muscle coactivation had a significantly longer active second stage duration (60 AE 56 vs 28 AE 16 minutes, P < .001). Cox regression analysis, adjusted for maternal age and epidural analgesia, demonstrated an independent significant correlation between levator ani muscle coactivation and a longer active second stage of labor (hazard ratio, 2.085; 95% confidence interval, 1.158e3.752; P ¼ .014). There was no significant difference between women who underwent operative delivery (n ¼ 46) when compared with the spontaneous vaginal delivery group (n ¼ 92) as regards anteroposterior diameter of the levator hiatus at rest and at Valsalva maneuver, nor in the prevalence of levator ani muscle coactivation (10/46 vs 15/92; P ¼ .49). CONCLUSION: Levator ani coactivation is associated with a longer active second stage of labor.

Descent of fetal head during active pushing: secondary analysis of prospective cohort study investigating ultrasound examination before operative vaginal delivery

“…We believe that fetal head movement upwards in the birth canal during pushing can be explained by levator ani muscle coactivation instead of relaxation. The effect of coactivation on labor has been assessed recently. Youssef et al .…”

“…and Kamel et al . examined nulliparous women at term before onset of labor and before induction of labor, respectively, and showed that women with coactivation had a significantly longer second stage of labor.…”

“…We believe that fetal head movement upwards in the birth canal during pushing can be explained by levator ani muscle coactivation instead of relaxation 19,20 . The effect of coactivation on labor has been assessed recently 21,22 . Youssef et al and Kamel et al examined nulliparous women at term before onset of labor and before induction of labor, respectively, and showed that women with coactivation had a significantly longer second stage of labor 21,22 .…”

The dynamic change of the anteroposterior diameter of the levator hiatus under Valsalva maneuver at term and labor outcome

“…However, few data have shed the light on the role of the pelvic floor in the mechanism of birth 16,20 . Smaller pelvic floor dimensions were found to be associated with a longer second stage of labor, whereas the relationship between pelvic floor dimensions and the mode of delivery is less clear with conflicting data 15‐17,21,22 . The proportional change of the ADP of the levator hiatus has been found to be a reproducible indicator of pelvic floor contraction 10 .…”

“…Moreover, pelvic floor muscle relaxation seems essential for childbirth. LAM coactivation was recently found to be associated with longer second, active second stage of labor and with less engaged fetal head at term 15,17,22 . In a recent study conducted on women undergoing vacuum delivery, LAM coactivation was assumed to be the cause of lack of fetal head descent with maternal pushing 23 …”