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.

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.