Diagnosis of Abnormal Labor
INTRODUCTION 　

Background: In order to define abnormal labor, a definition of normal labor must be understood and accepted. Normal labor is defined as uterine contractions that result in progressive dilation and effacement of the cervix. By following thousands of labors resulting in uncomplicated vaginal deliveries, certain time limits and progress milestones have been identified. Failure to meet these milestones defines abnormal labor, which suggests an increased risk of an unfavorable outcome. Thus, abnormal labor alerts the obstetrician to consider alternative methods for a successful delivery that minimizes risks to both the mother and infant.

Friedman𠏋 original research in 1955 defined 3 stages of labor. The first stage starts with uterine contractions leading to complete cervical dilation, and it is divided into the latent and active phases. In the latent phase, there are irregular uterine contractions but slow and gradual cervical effacement and dilation. The active phase is evidenced by an increased rate of cervical dilation and fetal descent. This active phase usually starts at 3-4 cm cervical dilation and is subdivided into the acceleration, maximum slope, and deceleration phases. The second stage of labor ranges from complete dilation to the delivery of the infant. The third stage of labor involves delivery of the placenta.

Abnormal labor constitutes any findings that fall outside the accepted normal labor curve. However, we hesitate to apply the diagnosis of abnormal labor during the latent phase because confusing prodromal contractions for latent labor is easy.

Abnormal labor of the second stage often is a result of problems with one of the 3 P's.

Pathophysiology: A prolonged latent phase may result secondary to oversedation or entering labor early with a thickened or uneffaced cervix. It also may be misdiagnosed in the face of frequent prodromal contractions. Protraction of active labor is more easily diagnosed and is dependent upon the 3 Ps.

The first P, the passenger, may produce abnormal labor because of the infant𠏋 size (eg, macrosomia) or from malpresentation.

The second P, the pelvis, can cause abnormal labor because its contours may be too small or narrow to allow passage of the infant. Both the passenger and pelvis cause abnormal labor by a mechanical obstruction, referred to as dystocia.

Regarding the power component, the frequency of uterine contraction may be adequate but the intensity inadequate. Disruption of communication between adjacent segments of the uterus also may exist, resulting from surgical scarring, fibroids, or other conduction disruption. Whatever the cause, the contraction pattern fails to result in cervical effacement and dilatation.

Frequency:
　

Mortality/Morbidity: Both maternal and fetal mortality and morbidity increases with abnormal labor. This probably is an effect-effect relationship rather than a cause-effect relationship. Nonetheless, some urgency to identify abnormal labor and act appropriately to reduce these risks exists.

CLINICAL 　

History:

Physical:

Causes:

DIFFERENTIALS 　

Other Problems to be Considered:

False labor
Placental abruption
Premature labor

WORKUP 　

Lab Studies:
　

Imaging Studies:
　

Other Tests:
　

Procedures:
　
TREATMENT 　

Medical Care: A prolonged latent phase is not indicative of dystocia in itself because this diagnosis cannot be made in the latent phase. Gabbe stated the following:

　

For those in the latent phase, the treatment of choice is rest or sleep for several hours. During this interval uterine activity, fetal status and cervical effacement must be evaluated to determine if progress to the active phase has occurred. Approximately 85% of patients so treated will progress to the active phase. Approximately 10% will cease to have contractions, and the diagnosis of false labor may be made. For the approximately 5% of patients in whom therapeutic rest fails and in patients for whom expeditious delivery is indicated, oxytocin infusion may be used.

Surgical Care:

Diet:

Activity:

MEDICATION 　

A method called active management of labor is practiced in Ireland. This method is applied to women who are nulliparous with singleton cephalic presentations at term. It involves the use of high dose oxytocin, starting rate at 6 mU/min and increasing by 6 mU/min every 15 minutes to a maximum of 40 mU/min. The goal is no more than 7 uterine contractions per 15 minutes. Cesarean delivery is performed if delivery has not occurred or is not imminent 12 hours after admission or for fetal compromise (diagnosed with fetal scalp pH). Initially, the Irish cesarean section rate was quoted at 4.8% but now has doubled, which is attributed to widespread use of epidural anesthesia. Other studies using the active management protocol describe similar cesarean section rates to that of the low-dose protocol.

Dinoprostone and misoprostone are prostaglandin analogs used to stimulate cervical dilation and uterine contractions, and are pharmacologic alternatives to using laminaria or placing a Foley bulb in the cervix.
　

Drug Category: Abortifacients -- Oxytocin is the only Food and Drug Administration (FDA)-approved medication recommended for labor augmentation. Other options include misoprostol and dinoprostone.

Drug Name
　		 Oxytocin (Pitocin) -- Produces rhythmic uterine contractions and can stimulate the gravid uterus, as well as vasopressive and antidiuretic effects. Can also control postpartum bleeding or hemorrhage.
Has a half-life of 3-5 min and reaches steady state in approximately 40 min.
Adult Dose Common protocol: Start infusion at 1-2 mU/min and increase by 1-2 mU/min q30 min; continue until adequate contractions (>200 MVU/10 min) achieved or (at some institutions) a maximum rate of 20 mU/min is achieved
Pediatric Dose Not established
Contraindications Documented hypersensitivity; pregnant patients with severe toxemia; unfavorable fetal positions; a contracting uterus with hypertonic or hyperactive patterns; labor where vaginal delivery should be avoided such as invasive cervical carcinoma, cord presentation or prolapse, active herpes genitalis, total placenta previa, and vasa previa
Interactions Pressor effect of sympathomimetics may increase when used concomitantly with oxytocic drugs, causing postpartum hypertension
Pregnancy X - Contraindicated in pregnancy
Precautions A uterus that is overstimulated can be hazardous to both mother and fetus; hypertonic contractions can occur in a patient whose uterus is hypersensitive to oxytocin, regardless of whether it was administered appropriately; has intrinsic antidiuretic effect that when administered by continuous infusion and patient is receiving fluids by mouth, can cause water intoxication
Drug Name
　		 Misoprostol (Cytotec) -- Prostaglandin analog that causes cervix to thin and dilate and uterus to contract as it does during labor. Not FDA approved for this use.
Adult Dose 25-50 mcg tab inserted intravaginally (paracervically); may readminister after 4 h if patient reassessment is reassuring (<3 contractions/10 min)
Pediatric Dose Not established
Contraindications Documented hypersensitivity; do not administer if >3 uterine contractions/h or in patients with uterine scar (eg, previous cesarean section, myomectomy)
Interactions None reported
Pregnancy X - Contraindicated in pregnancy
Precautions A uterus that is overstimulated can be hazardous to both mother and fetus; hypertonic contractions can occur; therefore patient must be under continuous medical supervision; caution when exceeding 150-200 mcg; monitor for tachysystole of uterine contractions (if this occurs, medication should be washed out
of vagina with NS); not FDA approved for this indication
Drug Name
　		 Dinoprostone (Cervidil) -- Prostaglandin E2 causes cervix to thin and dilate and uterus to contract as it does during labor. Do not start oxytocin within 6 h of dinoprostone.
Adult Dose Gel: 0.5 mg/syringe intracervically or 10 mg vaginal insert placed in posterior vaginal fornix
(removed after active labor or after 12 h); reassess cervical change in 4-6
Pediatric Dose Not established
Contraindications Documented hypersensitivity
Interactions None reported
Pregnancy X - Contraindicated in pregnancy
Precautions A uterus that is overstimulated can be hazardous to both mother and fetus; hypertonic contractions can occur; therefore, patient must be under continuous medical supervision; abdominal or stomach cramps, diarrhea, fever, nausea, or vomiting may occur

Drug Category: Beta-adrenergic blocking agents -- Another option for abnormal labor secondary to inadequate uterine contractility is a beta-blocker. See Picture 4 for inclusion and exclusion criteria.

Drug Name
　		 Propranolol (Inderal) -- Nonselective, beta-adrenergic receptor blocker.
Adult Dose 2 mg IV; repeat one time only in 1 h if no progress observed
Pediatric Dose Not established
Contraindications Documented hypersensitivity; uncompensated congestive heart failure; bradycardia, cardiogenic shock; A-V conduction abnormalities
Interactions Coadministration with aluminum salts, barbiturates, NSAIDs, penicillins, calcium salts, cholestyramine, and rifampin may decrease propranolol effects; calcium channel blockers, cimetidine, loop diuretics, and MAOIs may increase toxicity of propranolol; toxicity of hydralazine, haloperidol, benzodiazepines, and phenothiazines may increase with propranolol
Pregnancy C - Safety for use during pregnancy has not been established.
Precautions Beta-adrenergic blockade may decrease signs of acute hypoglycemia and hyperthyroidism; abrupt withdrawal may exacerbate symptoms of hyperthyroidism, including thyroid storm; withdraw drug slowly and monitor closely
FOLLOW-UP 　

Complications:
　

Prognosis:
　

Patient Education:
　
MISCELLANEOUS 　

Medical/Legal Pitfalls:
　
BIBLIOGRAPHY