Determining when a woman is in labor and needs hospital admission can be difficult. The diagnosis of false labor is frustrating for the patient who is often uncomfortable and anxious. The temptation to admit a patient in the latent phase of labor to relieve her pain or soothe her fear is strong. However, there may be risks to admitting a woman in latent labor. Presenting to labor and delivery in the latent phase of labor is a risk factor for cesarean delivery.1 It is unclear, however, whether women who present in the latent phase of labor are destined to have dysfunctional labors at admission or whether latent phase admission increases risk of poor outcomes through prolonged exposure to the hospital and increased interventions.
The purpose of our study is to estimate whether women presenting in the latent phase of labor are different at admission from those presenting in the active phase of labor. If they are not different, we explore the idea that exposure to the hospital environment could be responsible for the increased risk of cesarean delivery in these women.
The Perinatal Database at MetroHealth Medical Center contains demographic, complication, labor course, and maternal and neonatal outcome information for every delivery occurring at this institution. After obtaining institutional review board approval and a Health Insurance Portability and Accountability Act waiver, we limited these data to women delivering between January 1993 and June 2001 (N = 24,970). We excluded women with a prior cesarean delivery, rupture of membranes at presentation, contraindications for vaginal delivery, medical or obstetric complications during pregnancy, induction of labor, or known substance abuse. We further limited the data set to uncomplicated, term, singleton gestations with vertex presentation. After exclusions, 8,818 (35%) remained in the data set.
Active labor was defined as uterine contractions on admission with cervical dilatation of 4 cm or more without rupture of membranes. Latent phase was defined as contractions without rupture of membranes at less than 4 cm cervical dilatation. Although the exact dilatation that a women enters active phase varies from individual to individual, we chose 4 cm as a commonly accepted changeover point.
Demographic characteristics of women admitted in active and latent labor were compared using a Student t test or χ2 as appropriate. Cesarean delivery rates in latent and active phase labor groups were also compared using the χ2 test. Labor interventions and maternal and neonatal outcomes were compared between the active and latent labor groups. Last, labor outcomes were assessed by logistic regression, controlling for parity. Statistical analysis was performed on Stata 7.0 (StataCorp, College Station, TX). For this analysis a value of P < 0.01 was considered significant.
Among eligible gestations, there were 6,121 women admitted in active labor and 2,697 women admitted in latent labor. There were some significant differences between the labor groups. Women admitted in latent labor were more likely to be nulliparous and have slightly smaller babies. Latent labor admissions were also more likely to have private insurance (Table 1). However, differences in infant weight and private insurance, while statistically significant, were small. Differences in cervical dilatation, effacement, and station showed that we adequately discriminated between latent and active phase admissions in categorizing our data.
In this study population, the cesarean delivery rate among nulliparas was 10.1% and for multiparas was 1.8%. Because the latent labor group was more likely to be nulliparous, we stratified our results by parity. Nulliparous women arriving in latent phase had a 14.2% cesarean delivery rate (compared with 6.7% for nulliparas admitted in active labor; P < .0001). Among multiparous women, latent phase admission was associated with a cesarean delivery rate of 3.1% (compared with 1.4% for multiparas admitted in active labor; P < .0001).
Controlling for parity, women presenting in latent labor were more likely to have a diagnosis of active phase arrest (odds ratio [OR] 2.2, 95% confidence interval [CI] 1.6–3.1), use of oxytocin (OR 2.3, CI 21.–2.6), performance of scalp pH (OR 2.2, CI 1.8–2.6), placement of intrauterine pressure catheter (OR 2.2, CI 2.0–2.5), monitoring by fetal scalp electrode (OR1.7, CI 1.5–1.9), or amnionitis (OR 2.7, CI 1.5–4.7). There was no difference in rates of cesarean delivery for arrest of descent, low forceps delivery, mid forceps delivery, vacuum extraction, neonatal intubation, postpartum hemorrhage, or postpartum infection (Table 2).
In this study, we evaluated the labor course of women admitted in latent or active phase of labor to examine the association between latent phase admission and subsequent outcome. We limited potentially confounding factors by restricting our data to low-risk, term gravidas who were candidates for vaginal delivery. We found latent phase admission to be associated with increased cesarean delivery rates, increased obstetric interventions, and increased infection rates. The latent and active phase labor groups in our study have similar characteristics at admission, allowing speculation that exposure to the medical system might be responsible for the differences in outcomes.
A large Irish cohort study2 of low-risk nulliparous women in spontaneous labor also suggests that cesarean deliveries are more frequent in women admitted at lesser dilatations. The authors demonstrated a cesarean rate of 6.3% in women arriving at less than or equal to 2 cm cervical dilatation, compared to a 0% cesarean rate in those women admitted at greater than 3cm cervical dilatation. (P < .01). All participating women were managed by active management of labor protocols and infant birth weights between the groups showed no differences.
We propose that there are 2 possible explanations as to why women arriving in latent labor have higher cesarean delivery rates and infection: either women who present in latent labor have an inherently higher risk of dysfunctional labor at baseline, or increased exposure to the medical system confers risks that were not present at admission. Women destined to have cesarean deliveries may have different labor experiences than those destined to have a vaginal delivery. Need for more labor analgesia has been linked to dysfunctional labor.3 This pain difference may influence women with dysfunctional labor patterns to go to the hospital sooner than women experiencing a normal labor. Undocumented baseline differences between groups are always a potential confounder in cohort studies. A randomized trial is needed to insure comparability of the groups at baseline.
There has been 1 small randomized trial of latent compared with active phase admission for labor. McNiven et al4 randomly assigned 209 women who presented to triage in latent labor to latent compared with active phase admission. Patients arriving in latent phase were randomly assigned to either admission to labor and delivery directly from triage or sent home to return later in active labor. Although this study did not have the power to evaluate adequately the primary outcome of cesarean delivery, women admitted in early labor had a cesarean delivery rate of 10.6%, whereas those admitted in active labor had a cesarean delivery rate of 7.6%. Additionally, the study showed a statistically significant increase in oxytocin use and epidural administration among women admitted in early labor. The authors also demonstrated that women admitted in active labor had a better opinion of their labor experience than those admitted in latent labor. Because patients were randomly assigned, their findings suggest that it is the exposure to the hospital and not inherent patient characteristics that are responsible for the increased cesarean delivery, epidural, and oxytocin rates. A larger prospective, randomized trial would be needed to confirm whether exposure to the medical system confers additional risk to the patient admitted in latent phase labor.
Due to our retrospective cohort study design, we cannot rule out that there is an undetected baseline difference between the 2 groups in our study leading to the noted differences in cesarean delivery and interventions. However, our study adds to the evidence that a larger randomized trial should be performed to evaluate the possibility that exposure to the health care system confers risk, and to determine which, if any, interventions lead to this additional risk.