The transition from latent to active labor and adverse obstetrical outcomes

BACKGROUND: Recommendations on preventing the primary cesarean delivery removed the previously defined time limits for latent labor (defined as ending at 6 cm) and urged clinicians to avoid cesarean delivery for labor abnormalities in the latent phase. However, relatively little is known about the implications of labor curve abnormalities from 4 cm to 6 cm and subsequent outcomes. OBJECTIVE: To examine the association between length of time for dilation from 4 cm to 6 cm, delivery outcomes, and maternal and neonatal morbidity. STUDY DESIGN: This is a secondary analysis of a prospective cohort study of patients at ≥37 weeks presenting in spontaneous or induced labor with a non-anomalous living singleton in vertex presentation. Patients with a history of cesarean delivery or who did not achieve 6 cm dilation were excluded. We used interval censored regression to determine the 90(th)percentile for dilation time from 4 cm to 6 cm and used logistic regression to estimate the odds ratios and 95% confidence intervals for adverse outcomes for patients above the these cutoffs percentile compared to those at or below. Analyses were adjusted for obesity, nulliparity, race, hypertension, diabetes, and type of labor (induced vs. spontaneous/augmented). Outcomes included cesarean delivery, maternal morbidity (composite of postpartum fever, wound infection, hemorrhage), and neonatal morbidity (composite of neonatal death, hypothermic therapy, mechanical ventilation, respiratory distress, meconium aspiration syndrome, seizure, or treatment of sepsis). Additionally, we created receiver operator characteristic curves to predict cesarean delivery, and maternal and neonatal morbidity based on time to dilate from 4 cm to 6 cm. The cutoff for time for each outcome was identified using the Youden index to maximize sensitivity and specificity, and test characteristics were computed. RESULTS: There were 7,355 patients eligible for analysis, 728 (10%) had dilation times from 4 cm to 6 cm >10.3 hours, which was the 90(th) percentile, and 6627 (90%) had dilation times ≤ 10.3 hours. Having dilation time from 4 cm to 6 cm above the 90(th) percentile (10.3 h) was associated with cesarean (adjusted odds ratio 2.05 (95% confidence interval 1.67, 2.52)), composite maternal morbidity (adjusted odds ratio 1.48 (95% confidence interval 1.10, 2.00)), and composite neonatal morbidity (adjusted odds ratio 1.92 (95% confidence interval 1.52, 2.4.)). The area under the receiver operator characteristic curve for predicting cesarean delivery was 0.73 (95% confidence interval 0.71, 0.75). The test characteristics for the cutoff of 9.75 h were: sensitivity 68.3% (95% confidence interval 64.8%, 71.7%), specificity 66.2% (95% confidence interval (55.0%, 67.3%), positive predictive value 18.5% (95% confidence interval 17.1%, 20.0%), and negative predictive value 94.9% (95% confidence interval 94.2%, 95.5%). For composite maternal morbidity the cutoff was 6.98 hours and the area under the curve was 0.62 (95% confidence interval 0.59, 0.65), while for composite neonatal morbidity it was 5.5 hours (area under the curve 0.69, 95% confidence interval 0.67, 0.71). CONCLUSIONS: Patients whose dilation time from 4 cm to 6cm exceeds the 90(th) percentile have increased odds of cesarean delivery and postpartum complications. Prolonged dilation time has moderate predictive ability for adverse outcomes. Future studies should investigate at what point, if any, intervention is warranted during this period to reduce these risks.