Impact factors on cervical dilation rates in the first stage of labor.

AIMS: To assess cervical dilation rates of nulliparous and multiparous women in the active first stage of labor and to evaluate significant impact factors.

METHODS: In a retrospective cohort study between January 2007 and July 2014 at the University Hospital of Zurich in Switzerland, we analyzed 8378 women with singleton pregnancies in vertex presentation with a vaginal delivery at 34+0 to 42+5 gestational weeks. Median cervical dilation rates were calculated and different impact factors evaluated.

RESULTS: Cervical dilation rates increase during labor progress with faster rates in multiparous compared with nulliparous women (P<0.001). Dilation rates exceed 1 cm/h at a dilatation of 6-7 cm, but are very individual. Accelerating impact factors are multiparity, a greater amount of cervical dilation and fetal occipitoanterior position, whereas the use of epidural anesthesia, a higher fetal weight and head circumference decelerate dilation (P<0.001).

CONCLUSION: Cervical dilation is a hyperbolic increasing process, with faster dilation rates in multiparous compared to nulliparous women and a reversal point of labor around 6-7 cm, respectively. Besides, cervical dilation is highly individual and affected by several impact factors. The diagnosis of labor arrest or prolonged labor should therefore be based on such rates and on the individual evaluation of every woman.