What term describes a failure to quickly progress during the active stage of labor?

Obstetrical Forceps Delivery

Obstetrical forceps were first used by members of the Chamberlen family in the 17th century but were not widely accepted until 100 years later.343 William Smellie was the first to systematically teach the principles of forceps deliveries. It is clear that he also was fully aware of the potential dangers of the instruments; in the introduction to volume II ofTreatise on the Theory and Practice of Midwifery, he wrote, “If these expedients (forceps) are used prematurely when the nature of the case does not absolutely require such assistance, the mischief that may ensue will often over balance the service for which they were intended and this consideration is one of my principal motives for publishing this second volume.”344

In 1988, the ACOG issued a Committee Opinion establishing new definitions for obstetrical forceps.345 These definitions, which were incorporated in the 1991 ACOG Technical Bulletin entitledOperative Vaginal Delivery,346 were divided into three categories:

Outlet forceps

Scalp is visible at the introitus without separating labia

Fetal skull has reached pelvic floor

Sagittal suture is in anteroposterior diameter or right or left occiput anterior or posterior position

Fetal head is at or on perineum

Rotation does not exceed 45 degrees

Low forceps

Leading point of fetal skull is at station +2 cm or lower and not on the pelvic floor

Rotation is less than or equal to 45 degrees (left or right occiput anterior to occiput anterior or left or right occiput posterior to occiput posterior)

Rotation is greater than 45 degrees

Midforceps

Station is above +2 cm but head is engaged

This classification reflects what has been widely recognized among practicing obstetricians—that there are two types of forceps deliveries: low forceps deliveries, which are usually simple and uncomplicated for both mother and infant, and midforceps deliveries, which sometimes are difficult and can cause substantial trauma to either patient.

Introduction

Abnormal labor, which is usually referred to as dysfunctional labor, includes dystocia, which means difficult labor that is slow and not progressing. Dysfunctional labor can be due to abnormalities in uterine contraction and/or lack of ability of the mother to forcibly expel the fetus, a large fetus and/or an unusual orientation of the fetus in the uterus, or abnormalities in the pelvis such that the passage is blocked or too small. The latter may also be due to a disproportionate size of the fetus in relation to the size of the pelvis. Labor that is too rapid, referred to as precipitate labor, usually results from low resistance through the birth canal. The focus of this report is on dystocia since little is known about precipitate labor, it is rare, and there is no effective treatment for it.

Abnormal Timing of Labor

The timely onset of labor and birth is a critical determinant of perinatal outcome. Both preterm birth (defined as delivery before 37 0/7 weeks) and postterm (prolonged) pregnancy (defined as any pregnancy continuing beyond 42 0/7 weeks or 294 days dated from the first day of the last menstrual period) are associated with an increased risk of adverse pregnancy outcome.

Preterm birth is discussed in detail inChapter 7. Postterm pregnancy is associated with an increased risk of fetal macrosomia, fetal dysmaturity syndrome (caused by chronic intrauterine malnutrition), shoulder dystocia, perinatal mortality, and cesarean delivery. The perinatal mortality rate in fetuses without anomalies at 42 weeks or more of gestation is twice the rate at term, increasing fourfold at 43 weeks and fivefold to sevenfold at 44 weeks.277–279 Neonates born at 41 or more weeks of gestation experience one-third greater neonatal mortality than neonates born at 38 to 40 weeks.280 Although perinatal mortality does increase with increasing gestational age after 40 weeks, the absolute risk of fetal or neonatal death is low, estimated at 0.9 to 1.1 per 1000 ongoing pregnancies at 40 to 41 weeks, 1.2 to 1.3 per 1000 ongoing pregnancies at 41 to 42 weeks, 1.3 to 1.9 per 1000 ongoing pregnancies at 42 to 43 weeks, and 1.6 to 6.3 per 1000 ongoing pregnancies after 43 weeks.281–283 Uteroplacental insufficiency and cord compression leading to fetal hypoxia are thought to be the major causes, with smaller contributions from intrauterine infection and meconium aspiration.278,284 The long-term effects of postterm birth are unclear but may include an increased risk of neurologic injury (seizure disorders and cerebral palsy)285–287 and an increased risk of unexplained death in the first year of life (sudden infant death syndrome [SIDS]).282,288–290

Most postterm pregnancies have no known cause. However, the high rate of recurrent postterm pregnancy, apparent racial disparity (with rates being highest in non-Hispanic whites), and increased risk in patients with a family history of postterm pregnancy suggest that one-third to one-half of the variation in postterm birth in a population can be attributed to maternal or fetal genetic influences on the timing of labor.291–293 In rare instances, the cause of the postterm pregnancy is known and often involves a defect within the fetoplacental HPA axis, such as fetal anencephaly. The observation that human fetuses who fail to trigger labor at the appropriate gestational age allowing the pregnancy to continue into the postterm period have an increased risk of both antepartum stillbirth and unexplained death in the first year of life even in the absence of infection or meconium aspiration282,286–288 suggests that such fetuses may have subtle intrinsic abnormalities in their HPA axes that manifest later as SIDS.

Basic Information 

Dystocia and Malpresentation

Dystocia, or abnormal labor progression, accounts for one-third of all cesarean sections and half of primary cesarean sections. Because rapid surgical resolution is unavailable to the emergency clinician, intrapartum management skills are important.

Dystocia can be divided into three categories of causative factors. Labor fails to progress when there are problems related to: the pelvic architecture (the passage), fetal size or presentation problems (the passenger), and inadequate uterine expulsive forces. Although it is useful to consider these causes independently, dystocia is usually caused by a combination of factors. Presentation problems are particularly important because they become apparent during stage 2 of labor and require immediate action.

In order of increasing incidence, brow, face, shoulder, and breech presentations are the most common malpresentations (Table 181.2). True fetopelvic disproportion is much less common. Cesarean section is indicated when labor arrest or cord prolapse coexists with these presentations.

ETIOLOGY AND INCIDENCE

Dystocia comes from the Greek dys (difficult) and tokos (birth). Dystocia can be classified as functional or obstructive. Functional dystocia usually is termed inertia and can be classified as primary or secondary. Primary uterine inertia is the most common cause of dystocia in dogs and cats, with a reported incidence of up to 91% of cases.4,10,11 In primary uterine inertia, the myometrium produces weak, infrequent contractions resulting in a failure to deliver the fetuses. Primary uterine inertia can be further classified as complete or partial.12 In complete primary inertia, second stage labor does not start; whereas in partial primary inertia, second-stage labor starts but labor ends prematurely in the absence of obstructive causes.

Secondary uterine inertia occurs following a prolonged second stage of labor and may be associated with obstructive dystocia. Obstructive dystocia may result from relative or absolute fetal oversize. Absolute fetal oversize refers to a fetus that is too large to pass along a maternal birth canal that is of normal dimensions. Relative fetal oversize refers to a fetus of normal size that cannot pass along the maternal birth canal because the latter is abnormally small or restricted in some way. Relative fetal oversize is equivalent to a maternal obstructive dystocia. Known and speculated etiologies for both functional and obstructive dystocia are listed in Box 140-1.

Certain canine and feline breeds are overrepresented in cases of dystocia, with the incidence approaching 100% in some breeds. Bulldogs and other brachycephalic breeds, Cocker Spaniels, Dachshunds, Terrier breeds (e.g., Scottish, Aberdeen, Border), and Welsh Corgis have a higher incidence of dystocia than other breeds.2 Dystocia is reportedly rare in the Greyhound.13 The overall incidence of canine dystocia is approximately 5% of all pregnancies.3 The overall incidence of feline dystocia irrespective of breed is 5% to 8%.14 However, the incidence of dystocia is 18% to 20% in British Short-Haired, Cornish Rex, Devon Rex, Persian, and Siamese breeds.14 In addition, the relative risk of dystocia is higher in dolichocephalic and brachycephalic breeds compared with mesocephalics (Abyssinian, Burmese, and Manx).14

Dystocia

Dystocia is defined as labor exceeding 12 to 24 hours or whenever there are signs of difficulty. Dystocia occurs at a rate of about 1% in a large group of ferrets. Potential causes of dystocia include pregnancy in an older jill or an elevated environmental temperature (above 70°F [21°C]). Kits of very large size (more likely with small litter size), posterior or sideways presentation, and deformed or anasarcous fetuses may also promote dystocia.8 Depending on the underlying cause of dystocia, jills may be managed medically with oxytocin (5-10 IU IM) or surgically via cesarean section.37

Uterine Inertia

Uterine inertia may be the cause or the result of dystocia. Primary uterine inertia results from failure of the uterus to properly contract during parturition. The cause is suspected to be hypocalcemia, a hormonal imbalance at parturition, or an inability of the myometrium to properly respond to contraction signals. Secondary uterine inertia is the result of failure of contractions to empty the uterus, causing fatigue of the myometrium. This may be caused by incomplete cervical dilation, maldispositions, or conditions that block the birth canal. Depending on the underlying cause, relief is by mutation and traction, supplementation with calcium, or cesarean section. Oxytocin (10–20 IU) may be given in an attempt to stimulate contractions of the uterus, but response is usually poor in cases of uterine inertia.

Causes and Pathophysiology

I.

Uterine inertia and fetal malpresentation are the most frequently reported causes of dystocia in the queen (Ekstrand and Linde-Forseberg, 1994; Gunn-Moore and Thrusfield, 1995).

Uterine inertia

Primary uterine inertia is the failure to initiate labor at term.

Secondary uterine inertia is the failure to progress once labor is initiated (uterine fatigue).

Fetal malpresentation

Both anterior and posterior presentations are normal in the queen.

Common malpresentations include true breech, forward flexion of one hindlimb, flexion of head or neck, simultaneous presentation of two kittens, and transverse presentations (Ekstrand and Linde-Forsberg, 1994).

Dystocia is significantly more prevalent in purebred queens than mixed-breed queens.

Dolichocephalic and brachycephalic head types have higher rates of dystocia compared with mesocephalic head types (Gunn-Moore and Thrusfield, 1995).

Less common causes of dystocia in the queen include narrowed birth canal, oversized fetuses, and fetal malformation.

Dystocia from uterine torsion occurs uncommonly in the queen.

Incidence and Causes of Dystocia

Dystocia is relatively uncommon in alpacas and llamas, with fewer than 5% of birthings requiring assistance.1,2 The incidence of dystocia in camelids has been estimated to be between 2% and 5% of all births.2,8 In our practice, dystocia requiring major obstetric intervention represents less than 1% of all births (A. Tibary, personal observation). Early diagnosis of dystocia is very important because it may evolve rapidly to a critical situation endangering the life of both the fetus and the dam.

Dystocia should be suspected if the first stage of labor exceeds 6 hours with increasing signs of discomfort or if the second stage of labor does not progress normally within 10 minutes of the rupture of the amniotic sac. Dams may show signs of distress, with frequent alternation between the standing and sitting positions, side to side rolling, and excessive vocalization and straining. Abnormal (bloody or purulent) discharge in a term female warrants immediate obstetric evaluation. One rule that we always observe is to attend immediately to any parturient female that the owner says is not acting normally. In our opinion, experienced alpaca and llama owners have the best appreciation of the progression of the first stage of labor.

Dystocia of maternal origin may be caused by uterine inertia, small pelvic size, failure of cervical dilation, and uterine torsion. Failure of cervical dilation and uterine torsion are the most common causes of dystocia of maternal origin.2,8,9 Failure of cervical dilation is associated with long-term progesterone supplementation during pregnancy.7

Dystocia caused by the small size of the dam is rarely seen if females are bred for the first time when they reach at least 65% of adult weight and height. Narrowing of the birth canal may be caused by space-occupying lesions or masses. Uterine inertia, arising from weak or absent uterine contractions, is occasionally seen in older animals or in animals with prolonged pregnancy. Hypocalcemia may also be involved in secondary uterine inertia.

Dystocia of fetal origin is generally caused by fetomaternal disproportion (large fetus), fetal abnormalities, or abnormal presentation, position, or posture. We have observed a significant increase in dystocia from very high birth weights of crias in recent years, particularly in alpacas. The most common fetal malpositions are carpal flexion and lateral or ventral deviation of the head and neck. This is caused by the long neck and limbs of the fetus in these species. Unilateral or bilateral hack or hip flexions (breech) occur in posterior presentation. Dystocia caused by fetal abnormalities is rare. Cases seen in our clinic include schistosoma reflexus, ankylosis, and hydrocephalus. Other anomalies causing dystocia include fetal anasarca and emphysematous fetus resulting from death and maceration. Term twins are rare but should always be considered in cases of dystocia.