The duration of labor in healthy women.

OBJECTIVE: To measure the duration of active labor (first and second stages) in low-risk women whom received intrapartum care from certified nurse-midwives in nine hospital settings in the United States in 1996. Clinical factors and morbidity indicators associated with longer labors were also examined.
DESIGN: An observational study was conducted with healthy women at term who did not receive oxytocin or epidurals (n = 2511). Descriptive statistics are reported for the duration of the active phase--first stage (4 cm to complete cervical dilatation) and second stage (complete to delivery)--by parity and for subgroups of women according to race/ethnicity, age, insurance, activity in labor, type of fetal heart monitoring, and narcotic analgesia. Logistic regression was also used to assess the contribution of each variable to longer labors with simultaneous adjustment of the other variables.
RESULTS: The mean length of the active-phase, first stage was 7.7 hours for nulliparas and 5.6 hours for multiparas (statistical limits of 2 standard deviations from the mean were 17.5 and 13.8 hours, respectively). The mean length of second stage was 54 minutes for nulliparas and 18 minutes for multiparas (statistical limits 146 and 64 minutes, respectively). Variables associated with longer labors were electronic fetal monitoring, ambulation, maternal age over 30 years, and narcotic analgesia. Morbidity was not increased in longer labors.
CONCLUSION: Normal labor in healthy women lasted longer than many clinicians expect. The criteria for distinguishing normal from abnormal labor, based on time, need revision.