Refining the clinical definition of active phase arrest of dilation in nulliparous women to consider degree of cervical dilation as well as duration of arrest

Abstract

Background: Maternal and neonatal outcomes associated with duration of arrest of dilation beyond 4 hours are not well known. In addition, the current definition of arrest does not consider the degree of cervical dilation (6 cm vs 7 cm vs 8 cm vs 9 cm) when arrest occurs.

Objective: We sought to examine maternal and neonatal outcomes in nulliparous women who achieved the active phase of labor according to the duration they required to achieve a cervical change of at least 1 cm (<4 hours vs 4-5.9 hours vs ≥6 hours) beginning at 6, 7, 8 and 9 cm.

Study design: This was a retrospective cohort study of nulliparous women with term singleton cephalic pregnancies in spontaneous or induced active labor (≥6 cm). To evaluate the effect of labor duration on maternal and fetal outcomes at different degrees of cervical dilation, we categorized women based on time intervals they required to achieve a cervical change of at least 1 cm after membrane rupture ("<4 hours," "4-5.9 hours," and "≥6 hours"), and we correlated each time interval with referent cervical dilation status (6 cm, 7 cm, 8 cm, and 9 cm). Maternal and neonatal outcomes were analyzed according to the duration to progress at least 1 cm starting from each degree of cervical dilation. Our primary outcome was a composite of neonatal outcomes, including intensive care unit admission, neonatal death, seizure, ventilator use, birth injury, and neonatal asphyxia. In addition, we examined maternal outcomes. Adjusted odds ratios with 95% confidence intervals were calculated, controlling for predefined covariates.

Results: Of 31,505 nulliparous women included in this study, 13,142 (42%), 10,855 (34%), 11,761 (37%), and 17,049 (54%) reached documented cervical dilation of 6, 7, 8, and 9 cm, respectively. At cervical dilation of 6 or 7 cm, the arrest of dilation of <4 hours compared with arrest of dilation of 4 to 5.9 hours was associated with decreased risks of adverse maternal outcomes. When cervical dilation was 8 or 9 cm, arrest of dilation of <4 hours compared with arrest of dilation of 4 to 5.9 hours was associated with decreased risks of adverse maternal and neonatal outcomes. For example, women starting at a cervical dilation of 8 cm who required <4 hours to achieve a cervical change of 1 cm compared with those who required 4 to 5.9 hours had lower rates of cesarean delivery (adjusted odds ratio, 0.40; 95% confidence interval, 0.28-0.55), chorioamnionitis (adjusted odds ratio, 0.42; 95% confidence interval, 0.29-0.60), and the neonatal composite outcome (adjusted odds ratio, 0.51; 95% confidence interval, 0.36-0.72).

Conclusion: When cervical dilation is 6 or 7 cm, allowing arrest of dilation of ≥4 hours is reasonable because it was not associated with increased risks of adverse neonatal outcomes. When cervical dilation is 8 or 9 cm, the benefit of allowing arrest of dilation of ≥4 hours should be balanced against the risk of adverse maternal and neonatal outcomes.

Keywords: active labor; cervical change; duration of arrest of dilation.