Labor, Abnormal

Article Author:
Prabhcharan Gill
Article Editor:
James Van Hook MD
Updated:
10/27/2018 12:31:40 PM
PubMed Link:
Labor, Abnormal

Introduction

Normal labor is characterized by regular and painful uterine contractions that conclude in progressive in labor. A discussion on abnormal labor patterns is reviewed as abnormalities of the first stage (cervical dilation to complete cervical dilation) and the second stage (descent of the presenting part leading to delivery of the baby). The third stage of labor describes expulsion of the placenta. An overview of labor abnormalities encompasses all the stages of labor. First and second-stage abnormalities are described either as protraction disorders (which means that delivery is progressing but is lower than normal) or as arrest disorders (complete cessation in progress).  Abnormal third-stage labor meriting intervention is placenta retention beyond 30 minutes, as most third stages are concluded within the first 10 to 20 minutes of delivery.

Etiology

The normal progression of labor requires the three "Ps" which represent power from uterine contractions, adequate bony maternal pelvis as the passage, and finally the fetus as a passenger presenting itself in a favorable presentation. The size of the fetus and the capacity of the maternal pelvis are tested as uterine contractions provide propulsion. A deficiency in the uterine contractions is addressed easily with the judicious use of oxytocin. However, labor abnormalities due to unfavorable fetal pelvic dynamics lead to true dystocia requiring a cesarean delivery.

Epidemiology

The trend toward more cesarean sections in the developed countries has drawn attention to initiatives to minimize primary cesarean sections. In this regard, guidelines have been developed to guide more conservative management of the first and second stages of labor abnormalities (Obstetric care consensus: Safe prevention of the primary cesarean delivery-ACOG and SMFM, March 2014). After delivery of the baby, the third stage of labor opens the risk for postpartum hemorrhage leading to blood transfusions and maternal morbidity. In the United States, the rate of postpartum hemorrhage increased from 26% from 1994 through 2006 primarily due to increased risks of uterine atony.  However, the maternal motility from postpartum obstetric hemorrhage has decreased since the late 1980s to a little more than 10% of the total maternal modality in 2009. Increased and appropriate use of blood transfusions, as well as surgical approaches such as peripartum hysterectomy and compression sutures, have contributed favorably to this statistic.

Pathophysiology

Friedman originally established the labor curve for the first stage of labor; however, it has since been contemporized by Zhang et al. Using recent reference graphs, this stage of labor is not diagnosed until 6 cm cervical dilation. Before diagnosing the rest of cervical dilation in the first stage of labor, allow 4 hours to progress under adequate uterine activity (with oxytocin as necessary), but for no more than 6 hours. Prior to 6 cm dilation, the latent phase has a variable duration, and it is best to defer amniotomy or neuraxial anesthesia which brings a commitment to delivery and limits the scope of conservative management. In the second stage of labor, in the absence of neuraxial anesthesia, the nulliparous abdomen may be allowed to push for at least 3 hours. When an epidural is used, an additional 1 hour is provided.  Additionally, voluntary pushing in the second stage in women with an epidural may be allowed when the station of the fetal head is at or below the ischial spines.

Histopathology

Usually, histopathology is used for scenarios where postpartum hemorrhage has occurred. When a hysterectomy is performed for postpartum hemorrhage, the histopathology may return consistent with morbidly adherent placenta such as placenta accreta, increta, or percreta. On occasion, the placental histopathology may return as chorioamnionitis (with our without funisitis) which may be associated with postpartum atony leading to hemorrhage.

Toxicokinetics

Oxytocin is a key pharmacologic agent in the correction of abnormal labor patterns. Although oxytocin's first clinical usage was described in 1906 for postpartum hemorrhage, its molecular structure remained elusive until 1955, and 1 year later it became commercially available. Exogenous oxytocin responsiveness typically commences at 20 weeks and improves with advancing gestational age until 34 weeks when it appears to stabilize. The next peak in its sensitivity occurs in labor and this occurs primarily due to the recruitment of myometrial oxytocin receptors binding sites as well as receptor activation is based on elevating intracellular calcium. During spontaneous labor, the blood oxytocin concentration remains stable; however, the responsiveness increases. Oxytocin has a short plasma half-life between 3 to 6 minutes. It is been shown that oxytocin takes approximately 40 minutes to reach a steady state of plasma concentration; however, clinically it could be adjusted every 30 minutes. Oxytocin is utilized as a continuous intravenous administration using an infusion pump. This allows a continuous, precise control of the dosage. Standard institutional protocols are required to minimize adverse oxytocin administration. Of note, oxytocin-induced myometrial receptor desensitization has been demonstrated in animals; its clinical relevance is unknown. As placental perfusion occurs between contractions tachysystole (six or more contractions in a 10-minute window averaged over 10 minutes), it should be avoided as it may impact on fetal condition if uncorrected.  Maternal hyponatremia occurs only in extended exposures to a high dose of oxytocin, especially if administered in hypotonic solutions. The reason for this is based on its structure being similar to vasopressin in some regard and thus oxytocin cross-reacts with the renal vasopressin receptors. Hypotension has been shown to occur with bolus IV administrations.

History and Physical

Symptoms for the onset of preterm labor are reviewed, including a history of contractions that are progressively stronger and any history of leakage of fluid or passage of a mucous plug. Asking about recent vaginal bleeding is always a significant inquiry to exclude concerns for placental abruption. At admission to labor and delivery, prenatal records and obstetric history should be reviewed because these optimally inform the provider to the best intrapartum obstetric care. This care includes determination of the static gestational age. Abdominal examination is a key component of an obstetric exam as it provides an estimated fetal weight of the fetus and informs the provider the fetal presentation and the descent of the presenting part into the pelvis. The continuous monitoring of the external fetal heart rate provides insight into fetal well-being. A manual vaginal exam to evaluate maternal bony pelvis capacity and cervical dilation, as well as fetal pelvic dynamics, occurs at intervals.

Evaluation

The uterine activity is assessed by external tocometry and targeted at 3 to 5 contractions in the 10-minute window. The contractions should last 30 to 40 seconds to be effective. Internal intrauterine pressure assessment using a catheter could be utilized, in which case marked medial units are used and targeted at more than 200 Montevideo units in a 10-minute window. The monitoring of uterine contractions should be continuous during labor. The assessment of the fetal heart rate could be performed utilizing external or internal fetal heart rate monitoring.  An alternative is fetal heart rate auscultation every 15 minutes in the first stage of labor and after each contraction during the second stage of labor. In the interpretation of the fetal heart rate strip millimeters considered are baseline viability, basal heart rate, cardiac accelerations or decelerations, endocrine activity.  Strip abnormalities are characterized based on consideration of the above parameters.

Treatment / Management

The Obstetric Partogram is a composite graphic record of labor progress. Along with documentation of essential obstetric vital signs, it is used in developing confluent areas to control intrapartum care. The World Health Organization (WHO) recognizes this status as useful labor management that adequately draws attention to excessively prolonged labors. Partogram has increasingly fallen out of use.

Most labor and delivery unit will have an established protocol for administration of oxytocin that entails the administration of the proper medication and dosage, as well as criteria for an incremental increase as clinically warranted. The protocols also include monitoring maternal and fetal vital signs, as well as the atria, for discontinuation of the medication in the event of concern for tachycardia systole all fetal well-being. Such protocols allow collaborative care between the nursing staff and the obstetrician.

Pearls and Other Issues

During labor complications, cesarean deliveries can be a life-saving procedure and may become medically necessary. Cesarean section rates among the nulliparous, singleton, term gestation and vertex presentation (NSTV) are currently trending in most institutions and states. Diligent management of labor aspires to minimize variation between providers. Management may lower the average cesarean section rates in this population, and this can provide the best opportunity to improve outcomes and reduce costs. In 2012 the baseline NSTV cesarean birth rate was 27% in California, and the most recent rate available in 2015 was 25.6%. As an example, California aspires to reach its target rate of 23.9% or lower by 2022. Racial disparities such as non-Hispanic black women having disproportionately higher cesarean delivery is also a deserved focus of inquiry.