Labor: Diagnosis and management of the latent phase

INTRODUCTION — The first stage of labor can be viewed in terms of its two phases: latent and active.

A prolonged latent phase can be problematic for patients since spending most of the day or longer in latent phase can be very fatiguing and provoke anxiety. For this reason, various interventions are offered to aid patients having difficulty coping with a long latent phase and who choose to have an intervention.

The definition/diagnosis of the latent phase and options for managing patients in the latent phase will be reviewed here. Other aspects of normal and abnormal early labor are discussed separately:

●(See "Labor: Overview of normal and abnormal progression".)

●(See "Labor and delivery: Management of the normal first stage".)

●(See "Labor: Diagnosis and management of an abnormal first stage".)

DEFINITION/DIAGNOSIS OF THE LATENT PHASE

Definition — The latent phase is the interval between the onset of labor and the beginning of the active phase. It is characterized by contractions, cervical softening or effacement, and slow cervical dilation.

Diagnosis — The diagnosis of latent phase is based on presence of contractions, cervical dilation <6 cm on digital examination, slow cervical change, and clinician judgment. There is little consensus regarding absolute diagnostic criteria for either the beginning or end of the latent phase, except that patients with cervical dilation ≥6 cm who are contracting are generally thought to be in the active phase [1,2].

●Onset – The time of onset of the latent phase is difficult to determine because there is no clear objective or subjective finding that characterizes this moment. It is often considered to be the time the patient first perceives regular, persistent uterine contractions; cervical status is difficult to consider in describing onset because a patient cannot check their own cervix. Some clinicians prefer a more quantitative definition and consider the time the patient states that contractions began to occur every three to five minutes for at least one hour as the beginning of the latent phase. Others use the time of hospital admission, which usually truncates the duration since labor generally begins outside of the hospital. Adding to the confusion, pregnant people normally have periods of regular and irregular contractile activity and very gradual changes in the cervix beginning in the third trimester [3-6].

●End – The end of the latent phase occurs when the active phase begins (ie, the time when the rate of cervical dilation accelerates), but precise determination of this point in time is also problematic.

•Friedman/1950s data – Friedman, who first described the concept of a labor curve in the 1950s, found that the cervix typically dilated slowly (<1 cm/hour) until 3 to 4 cm dilation and then began to dilate more quickly, resulting in an inflection at 3 to 4 cm on a graph depicting the curve of cervical dilation over time (figure 1). This inflection point was the beginning of a steep increase in the slope of the curve and signified the beginning of the active phase.

•Contemporary data – Several decades later, Zhang and colleagues used contemporary data to construct a labor curve and found that pregnant people entered the active phase at various cervical dilations with no clear or consistent inflection point (figure 2); however, almost all nulliparas and multiparas had more rapid rates of cervical dilation by the time the cervix was ≥6 cm dilated [7]. Based on Zhang's data, the practical clinical concept that has emerged is that all patients can be considered to have completed the latent phase and begun the active phase when they have reached ≥6 cm dilation, although some will have begun the active phase before 6 cm. One exception is when mechanical dilation is used for labor induction. Mechanical dilation may result in 6 cm cervical dilation without coinciding cervical effacement and contractions, and the patient does not seem to be in active labor. (See "Labor: Overview of normal and abnormal progression", section on 'What is normal labor progression?'.)

Differential diagnosis — The primary condition in differential diagnosis is "false labor," which is defined as regular or irregular painful contractions that are not associated with cervical dilation (also sometimes referred to as "Braxton-Hicks contractions"). Both false labor and the latent phase initially share similar characteristics of painful contractions associated with <6 cm cervical dilation and no obvious cervical change. However, the contractions associated with latent labor usually become stronger, more regular, and more frequent over time and do lead to cervical change. False labor or Braxton-Hicks contractions wane or cease over time and are not associated with cervical change. False labor may precede the latent phase of labor.

DURATION

Normal versus prolonged — No uniformly accepted contemporary criteria exist for the normal duration of the latent phase. As discussed above, the times for the onset of the latent phase and the transition from the latent phase to the active phase cannot be determined precisely and are subjective, so determining the duration of a normal latent phase is problematic.

Latent phase can be considered prolonged when the duration exceeds the 95^th percentile.

●Friedman/1950s data – Friedman considered the latent phase prolonged in parturients who had not entered the active phase by the 95^th percentile for duration of the latent phase in pregnant people in spontaneous labor. In nulliparas, this was 20 hours and in multiparas, 14 hours [8,9]. Friedman defined the beginning of the latent phase as the time when the patient felt significant, regular uterine contractions and a clinician noted slow cervical dilation; the end of the latent phase (ie, the beginning of the active phase) was the time of the upswing in the cervical dilation over time curve.

●Contemporary data – Contemporary data show that many pregnant people with latent phases longer than the upper limit of normal historically described by Friedman go on to have a normal active phase and vaginal birth, which suggests that Friedman's definition is too narrow [7]. A contemporary prospective study including nearly 1300 healthy, predominately White participants noted that the latent phase was 10 hours longer than Friedman described [10]. In this study, the 95^th percentile in nulliparas was 30 hours (median 9 hours) and in multiparas, 24.5 hours (median 6.8 hours). The beginning of the latent phase was measured from the patient’s first recognition of symptoms and the end was clinician assessment that the patient had entered the active phase on the basis of symptoms and cervical dilation.

In a large contemporary retrospective study, the duration of the latent phase was defined as the time from labor unit admission to cervical dilation of 6 cm [11]. The 95th percentile for the latent phase in nulliparas was 15.7 hours for those admitted with cervical dilation 2 to 2.5 cm and progressively fell to 4.5 hours for those admitted with cervical dilation 5 to 5.5 cm.

Although active phase and second-stage arrest are clinical entities, latent phase arrest is not, given the slowness of the latent phase.

Factors affecting the duration — The duration of the latent phase is highly variable and affected by internal and external factors, many of which are undefined.

Factors associated with a shorter latent phase durations include:

●A favorable cervix (eg, a cervix with a Bishop score ≥6) at the onset of labor shortens the latent phase [12]. In contrast, one-half of pregnant people who enter the latent phase with an unfavorable cervix (Bishop score <6) have a prolonged latent phase by Friedman's definition [13].

●Neuraxial anesthesia. In a randomized trial, the duration of the first stage of labor was shorter in patients who received neuraxial anesthesia with opioids than in those who received systemic opioids [14]. Approximately 95 percent of patients who had an epidural received it when they were ≤3 cm dilated. (See "Adverse effects of neuraxial analgesia and anesthesia for obstetrics", section on 'Effects on the progress and outcome of labor'.)

Factors associated with a longer latent phase durations include:

●Abnormal fetal positions, such as occiput transverse and posterior position.

Factors without a clear effect on latent phase duration include:

●Maternal age

●Pelvic capacity

●Gestational age

●Newborn weight  

EFFECT OF DURATION ON RISK FOR CESAREAN BIRTH AND OTHER OBSTETRIC OUTCOMES — Although a long latent phase as defined by Friedman has been associated with an increased risk for cesarean birth, this observation is not consistent across studies [15-18]. Most pregnant people in spontaneous labor with a long latent phase eventually enter the active phase with expectant management, oxytocin administration, or therapeutic rest, or they will stop contracting because they were in false labor. (See "Labor: Overview of normal and abnormal progression".)

One possible reason for reports of an increased risk for cesarean birth is that a prolonged latent phase may be misdiagnosed as a protraction or arrest disorder in the active phase. As a result, a cesarean birth may be performed inappropriately for failure to progress during latent labor or even false labor. To prevent the occurrence of latent phase cesarean birth for failure to progress the American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM) in 2014 jointly advised only making a diagnosis of first-stage arrest in patients with cervical dilation ≥6 cm (ie, in the active phase), ruptured membranes, and no cervical change over a period of at least four to six hours [19]. A subsequent retrospective cohort study reported that this paradigm shift was associated with a 50 percent reduction in the cesarean birth rate for arrest of labor in the first stage at their university hospital, without an adverse impact on maternal or neonatal outcomes [20]. ACOG and SMFM continue to advise against cesarean birth performed for a prolonged latent phase in the setting of reassuring maternal and fetal status [2].

A longer latent phase duration has also been associated with adverse outcomes other than cesarean birth. In a population-based cohort study, these outcomes included more frequent dystocia diagnosis and related interventions (eg, oxytocin augmentation, amniotomy, epidural anesthesia) during the active phase or second stage of labor in both nulliparas and multiparas, and increased risk of chorioamnionitis and occiput posterior position in nulliparas [5].

MANAGEMENT ISSUES

Should pregnant people in the latent phase be at home or in the hospital? — Generally, the latent phase is best experienced at home because studies consistently report that patients with low-risk pregnancies admitted to the labor unit in the latent phase are more likely to have interventions such as oxytocin augmentation, epidural analgesia, and cesarean birth than those admitted in the active phase [21-25]. The reasons for this difference are not clear but may include inherent labor abnormalities of individuals who present to the hospital early, misdiagnosis of active labor, the effect of the hospital environment, provider impatience, and institutional policies unfavorable to the care of patients in early labor [26].

When delaying admission until the active phase, it is important to balance the advantage of reducing potentially unnecessary interventions versus the disadvantage that some patients find it difficult to cope at home and desire the physical presence and intervention of their clinical provider [26,27]. We make the decision to admit or discharge home based upon our assessment of the patient (eg, psychological state, fatigue, tolerance of pain, parity, cervical status, medical and obstetric problems, distance from the hospital), fetal status, and, to a lesser extent, bed availability. Measures to help admitted patients cope are reviewed below.

A general discussion of timing of labor unit admission is available separately. (See "Labor and delivery: Management of the normal first stage", section on 'When should the low-risk parturient be admitted?'.)

Management of pregnant people who are having difficulty coping with a long latent phase

General approach — Approximately 5 percent of pregnant people can anticipate a latent phase that extends for many hours or days, assuming the duration of the latent phase follows a normal Gaussian distribution [13]. They may have frequent painful contractions and present to labor triage. If no cervical change occurs during a period of observation, they are usually sent home after a discussion about the normality of the slow process; support from health care providers; hydration, if appropriate; and advice about comfort measures (eg, massage, water immersion) [28]. Some such patients repetitively return to the labor unit and become increasingly tired and frustrated. It is our practice to offer admission to these patients as this type of latent phase can be physically and emotionally exhausting. Another common practice is to offer a sedative to help the patient fall asleep at home. One option is zolpidem 5 mg orally, which results in low but detectable umbilical cord concentrations when taken less than 11 hours prior to giving birth [29]. Neonatal sequelae are possible but unlikely after a single maternal dose used for this purpose.

More interventionist approaches for spontaneously laboring patients who are not tolerating latent phase include:

●Parenteral opioids for therapeutic rest (see 'Therapeutic rest' below)

●Oxytocin augmentation, with or without amniotomy and with or without epidural anesthesia (see 'Oxytocin administration' below)

The use of one or more of these measures is a shared decision between the patient and provider. Our preference is to give opioids for therapeutic rest to patients who are tired and uncomfortable in early latent phase and oxytocin for patients who are well rested or have already received therapeutic rest. Nonintervention is also an option.

Before considering these options, it is important to evaluate for potential coexistent obstetric problems. For example, therapeutic rest is not appropriate if there are maternal or fetal indications for delivery, such as preeclampsia, placental abruption, chorioamnionitis, or an abnormal fetal heart rate pattern. Oxytocin may not be appropriate if there is a fetal malpresentation or a hysterotomy scar.

Therapeutic rest — Therapeutic rest involves administration of parenteral opioids or sedatives to relieve the patient's discomfort and allow for progression of labor while they sleep or rest comfortably. Opioids are particularly useful in patients who are tired, uncomfortable, and in early latent phase. At many hospitals, these patients are placed in an observation area for rest, rather than admitting them to labor and delivery, which has cost implications. In Denmark, patients may take medication for therapeutic rest at home [30].

After ensuring maternal and fetal well-being, morphine or another opioid is administered. We give morphine 5 to 10 mg intramuscularly and intravenously simultaneously, not to exceed a total dose of 20 mg. Friedman's therapeutic rest regimen was 15 mg subcutaneously; if respirations were not depressed and the contractions were continuing without cervical change after 20 minutes, an additional 10 mg could be given (for patients with obesity, initial and repeat doses were increased by 5 mg) [13]. This was expected to result in 6 to 10 hours of sleep.

In one review, approximately 85 percent of pregnant patients in the latent phase treated with opioids woke up in the active phase of labor, 10 percent were not in labor (suggesting a diagnosis of false labor), and 5 percent had a persistent dysfunctional contraction pattern [31]. A more contemporary study reported 62 percent woke up in active labor [32].

The potential for addiction in patients offered opioids is a concern but highly unlikely after one dose prescribed for a medical indication [33,34].

Oxytocin administration — Administration of oxytocin appears to aid progression of labor from the latent to active phase [18]. In his classic report, Friedman concluded that oxytocin and therapeutic rest were equally efficacious and safe in correcting a prolonged latent phase [13]. For patients in latent phase, the average time between initiation of oxytocin and active labor was 3.4 hours.

There are no contemporary studies of the effect of oxytocin administration on the latent phase of patients in spontaneous labor, but data from patients with unfavorable cervixes undergoing induction suggest that it is effective: approximately 70 percent of patients exited the latent phase after 6 hours of oxytocin and membrane rupture, and only 5 percent remained in the latent phase after 12 hours [35]. This latter group was at high risk of cesarean delivery (only 40 percent delivered vaginally after 12 hours of oxytocin in the latent phase). The Consortium of Safe Labor study reported similar findings [36]. Among nulliparous patients undergoing induction of labor with an unfavorable cervix (defined as initial cervical dilation ≤2 cm) and rupture of membranes, only 6.5 percent had not exited the latent phase (ie, achieved cervical dilation ≥6 cm) by 12 hours; among multiparous patients, only 1.5 percent had not exited the latent phase by this time point. The rates of vaginal birth in these patients were 36.6 and 61 percent, respectively.

Prostaglandins, although widely used for cervical ripening and labor induction, have not been studied as a treatment for patients with a prolonged latent phase.

The ARRIVE trial supports the decision to stimulate labor as the findings suggest that low-risk nulliparous pregnant people and their newborns can benefit from labor induction at 39 weeks as compared with expectant management [37].

Role of epidural anesthesia — If the patient is committed to giving birth, then epidural anesthesia can be administered to provide deep relief and thus allow rest while oxytocin is being administered. Use of both oxytocin and epidural anesthesia essentially commits the patient to giving birth, whereas use of oxytocin alone can be stopped if labor does not progress and then restarted.

Role of amniotomy — Amniotomy has been reported to shorten the latent phase when used in active management of labor protocols, but most of the observed effect is thought to be related to oxytocin administration, which is often begun shortly after amniotomy in these protocols [38]. A small randomized trial limited to patients with prolonged latent phase by Friedman's definition noted that the combination of oxytocin and amniotomy significantly reduced the time from initiation of augmentation until delivery compared with either intervention alone [39].

Amniotomy alone is not useful. The lack of efficacy of amniotomy alone for accelerating spontaneous labor in patients with normal or prolonged latent phase was demonstrated in a meta-analysis of 15 randomized trials involving 5583 pregnant people [40]. Planned amniotomy did not significantly shorten the duration of the first stage of labor compared with planned "no amniotomy" (weighted mean difference -20.4 minutes, 95% CI -95.9 to 55.1 minutes). The lack of effect may be because, although amniotomy is associated with an increase in maternal plasma prostaglandin concentration [41], the effects on the uterus and cervix are probably insufficient to result in significant augmentation of labor. Moreover, rupture of membranes diminishes the pressure of the bulging gestational sac against the cervix, which may adversely affect ripening, effacement, and dilation of the cervix [42].

SPECIAL POPULATIONS

Induced labor — The duration of the latent phase appears to be longer in induced than in spontaneous labor [43-46]. Although heterogeneity of induction methods, indications for induction, and socioeconomic factors complicate any analysis of latent phase duration during induction, a plausible explanation for the apparent increase in duration is that the normal biochemical and biomechanical processes that occur during spontaneous labor are distorted during an induction.

Pragmatic criteria for normal latent phase duration have been developed to avoid cesarean birth for failed induction in patients who are still in the latent phase. These criteria and the evidence supporting them are reviewed separately. (See "Induction of labor with oxytocin", section on 'Definition of failed induction'.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Labor".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topics (see "Patient education: Labor and childbirth (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Definition/diagnosis – The latent phase is the initial phase of the first stage of labor when cervical dilation is slow. The time of onset can be defined as when the individual first perceives regular painful uterine contractions. The end of the latent phase occurs when the active phase begins, which generally occurs by 6 cm dilation. (See 'Definition/diagnosis of the latent phase' above.)

There are no uniformly accepted contemporary criteria for the normal duration of the latent phase. (See 'Duration' above.)

●Management

•Counseling and comfort measures – A long latent phase can be physically and emotionally exhausting. Routine measures include discussion about the normality of the slow process, support from health care providers, comfort measures (eg, massage, water immersion, oral sedative), and hydration, if appropriate. (See 'General approach' above.)

•Home versus hospital care – The decision to observe a patient in latent phase in the hospital or to send them home is based upon the provider's assessment of the patient (eg, psychological state, fatigue, tolerance of pain, parity, cervical status, medical and obstetric problems, distance from the hospital), fetal status, and, to a lesser extent, bed availability. (See 'Should pregnant people in the latent phase be at home or in the hospital?' above.)

•Options for intervention – Management options for patients who are not tolerating latent phase include therapeutic rest, oxytocin with or without amniotomy and with or without epidural anesthesia, and no intervention. Cesarean birth should not be a primary treatment for laboring patients not tolerating latent phase. The choice of intervention or nonintervention is based on the patient's values and preferences.

-Therapeutic rest – Therapeutic rest can be helpful for patients who are very tired and uncomfortable in early latent phase. Morphine 5 to 10 mg intramuscularly and intravenously simultaneously, not to exceed 20 mg, gives temporary relief by providing good analgesia and sedation. Approximately 85 percent of patients treated with this regimen will wake up in the active phase of labor. (See 'Therapeutic rest' above.)

-Oxytocin – Oxytocin with or without amniotomy is a good option for a patient who is well rested or has already received therapeutic rest and is now ready to cope with the demands of labor. The combination of oxytocin and epidural anesthesia is a good option for patients who are committed to giving birth during the hospitalization. (See 'Role of epidural anesthesia' above.)

●Outcome – Cesarean birth for failure to progress should not be performed during the latent phase of spontaneous labor. Most patients with a long latent phase eventually enter the active phase with expectant management, oxytocin administration, and/or amniotomy, or they will stop contracting because they were in false labor. (See 'Effect of duration on risk for cesarean birth and other obstetric outcomes' above.)