Dystocia - Abnormalities of the Expulsive Forces

Chapter 17. Dystocia : Abnormalities of the Expulsive Forces

May 17. 1999

Oh Sang Yun M.D

I. Introduction

Dystocia - difficult labor, abnormally slow progress of labor

The consequence of four distinct abnormalities

1. Abnormalities of the expulsive forces :

uterine forces insufficiently strong or inappropriately coordinated to efface and dilate the cervix inadequate voluntary muscle effort during the second stage of labor

2. Abnormalities of presentation, position, or development of the fetus

3. Abnormalities of the maternal bony pelvis

4. Abnormalities of the birth canal other than those of the bony pelvis

Dystocia is the most common contemporary indication for primary cesarean delivery

II. Labor Diagnosis

The strict definition of labor - uterine contractions that bring about demonstrable effacement and dilatation of the cervix

Recognizing its start

1. to instruct the woman to quantify contractions for some specified period

   -> define labor onset as the clock time when painful contractions become regular : very subjective

2. to define the onset of labor to begin at the time of admission to the labor unit

Admission criteria ( by National Maternity Hospital in Dublin )

  - painful uterine contractions accompanied by any one of the following ;

  1. ruptured membranes

  2. bloody show

  3.complete cervical effacement : in US, 3 - 4 cm or greater

A. First Stage of Labor

Friedman developed the concept of three functional divisions of labor (F 17-2)


1. Preparatory division : changes of the connective tissue components of the cervix

   sensitive to sedation and  conduction analgesia

2. Dilatational division : dilatation of the cervix

   not sensitive to sedation and conduction analgesia

3. Pelvic division : cardinal fetal movements in the cephalic presentation take place principally during this phase

Friedman subdivided the active phase into the acceleration phase, phase of maximum slope, and the deceleration phase

a. Latent Phase

- commences with maternal perception of regular contractions

- accompanied by progressive, slow, cervical dilatation and ends at between 3 and 5 cm of dilatation

Prolonged latent phase : > 20 hr in the nullipara and > 14 hr in the parous woman

   Factors that affect duration of the latent phase

          excessive sedation or conduction analgesia

          poor cervical condition

          false labor

   Management : rest and strong sedatives

-> 85 % begin active labor

-> 10 % cease contractions

-> 5 % recur an abnormal latent phase -> require oxytocin stimulation

   Amniotomy was discouraged during this phase

   Fetal and Maternal Effect of prolongation : not influence morbidity and mortality

b. Active Labor

- a rapid change in the slope of cervical dilatation between 3 and 4 cm

- the mean duration of active phase labor in nulliparas was 4.9 hours (Friedman 1955)

- the rate of dilatation

1.2 cm/hr is the minimum normal rate in the nullipara

1.5 cm/hr is the minimum normal rate in the multipara

- active labor phase abnormalities - the most common abnormalities of labor

incidence : in nullipara, 25% vs in multipara, 15%

classification : protraction, arrest (Friedman 1972) (T17-1)

 associated factors of active labor phase abnormalities

/ excessive sedation or conduction analgesia

/ fetal malposition (e.g., persistent occiput posterior)

  The majority of active phase disorders did not result in cesarean delivery -  only about 2 % of the 500 women studies (Friedman 1955)

B. Second Stage of Labor

- begin when cervical dilatation is complete and ends with fetal expulsion

- median duration : in nulliparas - 50 min, in multiparas - 20 min, but it is variable

- average second stage labor was lengthened about 25 minutes by regional analgesia

- limit of the length of the second stage : in nulliparas - 2 hours and extended to 3 hours when regional analgesia

in multiparas - 1 hour and extended to 2 hours with regional analgesia

- The relationship between the duration of second stage labor and pregnancy outcome :

1. maternal effects : postpartum hemorrhage and infection increased but incidence is quite small

2. infant effects (T 17-2)

           They concluded that there is no compelling reason to intervene with a possibly difficult forceps or vacuum extraction but after 3 hours in the second stage, delivery by cesarean or other operative method increased

III. Uterine Dysfunction

- characterized by lack of progress

- in the latent phase, the diagnosis is difficult

- one of the most common errors is to treat women for uterine dysfunction who are not yet in active labor

- There have been three significant advances in the treatment of uterine dysfunction:

       1. improvement of perinatal morbidity and mortality

       2. dilute intravenous infusion of oxytocin

       3. more frequent use of cesarean delivery rather than difficult midforceps delivery

A. Types of Dysfunction

- the lower limit of contraction pressure required to dilate the cervix is 15 mmHg

- normal spontaneous contractions often exert pressures of about 60 mmHg

- Two types of uterine dysfunctions

       1. hypotonic uterine dysfunction

       2. hypertonic uterine dysfunction or incoordinate uterine dysfunction

IV. Dystocia

Today, expression such as cephalopelvic disproportion and failure to progress are often used to describe

these dysfunctional labor when cesarean delivery is necessary

1. Cephalopelvic disproportion (CPD)

   - true CPD is rare and most CPD are due to malposition of the fetal head :

     asynclitism or extension of the bony diameters of the fetal head

   - inability to achieve vaginal delivery after reaching complete dilatation is a significant marker of true dystocia because it is likely to recur

2. Failure to progress

   - This term include lack of progressive cervical dilatation or lack of descent

   - The CPD and Failure to progress are not precise terms and we should use more

     practical terms, such as protraction or arrest

     The woman must be in the active phase of labor to diagnose either of these disorders

   - active phase arrest in 5 % of term nulliparas, this incidence has not changed since the 1950s ( Freidman 1978, Handa and Laros

   - Inadequate uterine contractions ( < 180 Montevideo units ) were diagnosed in 80 % of women with active-phase arrest

   - The World Health Organization(1994) has proposed a labor management

     'partograph' in which protraction is defined as less than 1 cm/hr cervical dilatation for a minimum of 4 hours

A. Overdiagnosis

   - Many cesarean deliveries were done for dystocia without a trial of labor (Stewart 1990)

   - Obstetricians with the lowest cesarean delivery rates for dystocia were those who used higher oxytocin dosages to stimulate labor, used oxytocin fort longer
durations and started oxytocin at more advanced cervical dilatations


B. Diagnosis of Active Phase Labor Disorders

   - Before the diagnosis of arrest during first stage labor is made, both of these criteria should be met :

  1. the latent phase has been completed, with the cervix dilated
4 cm or more

  2. a uterine contraction pattern of 200 Montevideo units or more in a 10-minute

   period has been present for 2 hours without cervical change

   - Epidural analgesia can slow labor

V. Ruptured Membranes Without Labor

- Membrane rupture without spontaneous uterine contractions -> about 8 % of terms

- Management : stimulation of contractions when labor did not begin after 6 to 12 hours  because of amnionitis

- Almost 75 % of those observed entered labor spontaneously within 24 hours

- The cesarean delivery rate was almost tripled in women undergoing labor induction ( Duff 1984 )

- In contrast, there was no advantage to delaying intervention because of neonatal infections ( Wagner 1989 )

- Prostaglandin E2 to reduce the  admission-to-delivery interval in nonlaboring women after membrane rupture at term (Chua 1995, Mahood and Dick 1995)

- Labor induction with intravenous oxytocin was the preferred management (Hannah 1996)

VI. Maternal Position during Labor and Delivery

- There is much disagreement concerning the potential influence of maternal position on labor progress, pain perception and fetal well-being

- uterine contractions occur more frequently but with less intensity with the mother in the supine position compared with lying on her side (Miller 1983)

- contraction frequency and intensity have been reported to increase with sitting or standing (Miller 1983)

- There is no conclusive evidence that upright maternal posture or ambulation improves labor (Lupe and Gross 1986)

VII. Labor Management Protocols

A. Active management of labor (O'Driscoll 1984)
- amniotomy and oxytocin

- Labor diagnosis : painful uterine contraction + complete cervical dilatation or bloody show or ruptured membranes

- Pelvic examination :

    /performed each hour for the next 3 hours -> 2 hour intervals

    /progress is assessed for the first time 1 hour after admission

- When dilatation has not increased by at least 1 cm, amniotomy is performed

- Progress is again assessed at 2 hours

    /if not significant progress (i.e., 1 cm/hr) -> high-dose oxytocin infusion

    /if membranes rupture prior to admission, oxytocin is begun for no progress

     at the 1-hour mark

- oxytocin infusion : < 10 units in 1 liter of dextrose, < 60 drops/min,

because of fetal distress

- The cesarean rate : 10.5 % with active management vs 14.1 % with the traditional approach ( Lopez 1992)

B. Parkland Hospital Labor Management protocol (F17-6)

- stipulate that pelvic examinations be performed approximately every 2 hours

- Cesarean rates in nulliparous and parous women were 8.7 and 1.5 %, respectively

- These labor interventions did not jeopardize the fetus-newborn infant

VIII. Oxytocin Stimulation of Labor

- synthetic polypeptide, mean half time - about 5 minutes

- for labor augmentation or induction

- Two questions before a treatment plan using oxytocin

  1. Has the woman actually been in active labor  

  2. Is there cephalopelvic disproportion  

A. Oxytocin Stimulation

- preparation : fetal heart rate and the contraction pattern be observed closely

- induction : stimulation of contractions before spontaneous onset of labor, with or without ruptured membranes

- augmentation : stimulation of contractions when spontaneous contractions are inadequate

B. Technique for intravenous Oxytocin

- should avoid uterine hyperstimulation and fetal distress

- discontinue if contractions exceed 5 in a 10 minute period or last longer than

   1 minute or if the fetal heart rate decelerates significantly

- discontinue if hyperstimulation

- uterine response - within 3 to 5 min after infusion

- steady state - within about 40 min

- response depends on following factors

preexisting uterine activity, sensitivity

cervical status

pregnancy duration : uterine response to oxytocin increases slowly from 20 to

30 weeks and is unchanged from 34 weeks until term

- Oxytocin has potent antidiuretic action :

when 20 mU/min or more is infused -> water intoxication - convulsions, coma, even death

IX. Amniotomy

- commonly used to induce or augment labor

- other common indications - internal electronic monitorings

- to minimize the risk of cord prolapse should be observed when membranes
are ruptured artificially and should avoid dislodging the fetal head

- An assistant applying fundal and suprapubic pressure may reduce the risk of cord prolapse. Some prefer to rupture membranes during a contraction.

- The fetal heart rate should be assessed prior to and immediately after the procedure

A. Elective Amniotomy

- hasten spontaneous labor and detect meconium

- amniotomy at 5 cm dilatation accelerated spontaneous labor 1 to 2 hours without

  increasing the overall rate of cesarean delivery or oxytocin

- oxytocin use was decreased when early elective amniotomy was performed

- There were no adverse fetal neonatal effects

X. Stripping Membranes

- induction of labor by this procedure is a common practice

- decreased incidence of postterm gestation

- significant increase in plasma prostaglandin form this procedure (McColgin 1993)

- Method :

        inserting the index finger as far through the internal os as possible and rotating twice through 360 degrees to separate the membranes from the lower segment

- ruptured membranes, infection, bleeding were not increased (Allott 1993)

XI. Prostaglandin E2

- kinds :

           local prostaglandin E2 gel (Prepidil)

           prostaglandin insert (dinoprostone)

           vaginal prostaglandin E2 (misoprostol)

- bring about cervical ripening, histological changes - dissolution of collagen bundles and an increase in submucosal water content

A. Clinical Effectiveness

- successful initial induction

  -decrease the incidence of prolonged labor

- reduce total and maximal oxytocin doses

- effects of prostaglandin on overall cesarean delivery rates

   -> not shown a significant decrease

B. Patient Selection

- Bishop score of 4 or less (T17-8)

- with intermediate scores (5 to 7) -> use has shown to trigger effective labor without subsequent need for oxytocin

C. Protocol for Administration

- continuous uterine activity and fetal heart rate monitoring can be performed

- remains recumbent for at least 30 minutes

- observation period : from 30 min to 2 hr

- contraction are usually apparent in the first hour and show peak activity in the first 4 hours (Bernstein 1991)

- oxytocin induction should be delayed for 6 to 12 hours

D. Side  Effects

- Uterine hyperstimulation

- Maternal systemic effects :

  fever, vomiting, diarrhea - negligible

  glaucoma, severe hepatic or renal impairment, asthma - caution

- Neonatal outcomes : not effect