Ultrasound assessment of cervical dynamics during the first stage of labor.

Objective: Assessment of cervical dynamics during the first stage of labor by a combination of ultrasound cervimetry and intrauterine tocography.

Methods: Sixty-two parturients were divided into four groups: nulliparous women in spontaneous (n = 9) or oxytocin-induced labor (n = 26), parous women in spontaneous (n = 11) or oxytocin-induced labor (n = 16). Intrauterine pressure and cervical dilatation were continuously recorded and assessed by off-line computer analysis.

Results: All women with spontaneous labor showed cervical responses to uterine contractions at the beginning of the recording. The first cervical response to a uterine contraction occurred at a significantly smaller dilatation in parous than in nulliparous women with induced labor (2.9 and 3.6 cm, respectively). Also, acceleration of cervical dilatation occurred at less dilatation in parous than in nulliparous women (3.4 cm and 4.8 cm, respectively), and myometrial work per cm of cervical dilatation was less in parous than in nulliparous parturients.

Conclusions: The results indicate significant differences between cervical dilatation patterns in nulliparous and parous women, which may be due to structural cervical changes caused by labor and parturition. The labor patterns found were different from those originally described by Friedman (Friedman EA. Graphic analysis of labor. Am J Obstet Gynecol 1954; 68: 1568-1575), as no deceleration phases were detected. Ultrasound cervimetry is a valuable technique for the study of cervical dynamics during labor.