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129: Early versus late admission to labor/delivery, labor progress and risk of caesarean section in nulliparous women

      Objective

      To examine whether early versus late admission to labor/delivery is associated with labor progress and risk of cesarean section (CS).

      Study Design

      We examined data on 1,329 nulliparous women with singleton vertex pregnancies and spontaneous labor onset. We selected three groups based on cervical dilation at admission: early (0.5-1.5 cm, N=178), intermediate (2.5-3.5 cm, N=320) and late (4.5-5.5 cm, N=175). Kaplan-Meier estimator of the incidence (adjusting for the censoring) was used for the analysis of interventions while random effects regression with splines was used for the assessment of labor progress.

      Results

      Women who were admitted to labor early were more likely to use oxytocin (77% versus 30% in late admission group) and had a higher risk of CS (18% versus 4%), while the risk of instrumental delivery did not differ (24% versus 24%). Before 4 cm dilatation, the earlier a woman was admitted to labor the higher her risk of CS was in a linear relationship. However, after 4 cm, the relationship disappeared. These patterns were true for both first and second stage CS. Once a woman who was admitted before 4 cm dilatation reached 5 cm without experiencing CS, she had a similar risk of CS as women who were admitted at 4.5-5.5 cm. Receiving oxytocin at an earlier stage of labor was associated with a higher risk of CS. Women admitted early had a longer duration of labor, but after 4 cm dilatation, their labor progressed faster than women who were admitted after 4 cm.

      Conclusion

      Early admission to labor/delivery was associated with longer labor and a significantly higher risk of CS. It remains to be elucidated whether this association was due to some underlying pathophysiology of dystocia or excessive intervention by physicians, or both. Understanding of this association may improve the strategy for reducing CS.