Active labor : As shown in figure 17-22, the progress of labor in nulliparous women has particular significance because these curves all reveal a rapid change in the slope of cervical dilatation rates between 3 and 5 cm. Thus, cervical dilatation of 3 to 5 cm or more, in the presence of uterine contractions, can be taken to reliably represent the threshold for active labor. Similarly, these curves provide useful guideposts for labor management.