Dystocia, or difficult birth, has an overall prevalence of approximately 5% to 6% of pregnancies in bitches and queens.
Dystocia, or difficult birth, has an overall prevalence of approximately 5% to 6% of pregnancies in bitches and queens. In certain breeds, however, the prevalence is much higher, approaching 18% in Devon Rex cats in the United Kingdom and 100% in English Bulldogs in the United States. It is a major cause of neonatal mortality in puppies and kittens. Overall mortality rates from birth to weaning average 12% (range 10% to 30%) in puppies and 13 % in kittens, but 65% of those losses occur at parturition and during the first week of life as a result of stillbirth, fetal stress, and hypoxia related to parturition.
The two most common causes of dystocia in small animals are (1) uterine inertia and (2) fetal malpresentation. Of these, uterine inertia is by far the most common, accounting for about 60% of all cases. Uterine inertia is the failure to develop and maintain uterine contractions sufficient for normal progression of labor. Uterine inertia has a variety of potential causes (e.g., genetic, age, nutrition, metabolic) but the specific cause for a particular case usually is not identified. The exception is mechanical obstruction that results in myometrial exhaustion and secondary uterine inertia. Fetal malpresentation accounts for approximately 15% of dystocia cases in bitches and queens.
Maternal causes of obstructive dystocia relate primarily to abnormalities in size or shape of the pelvic canal. Cephalo-pelvic disproportion, in which the fetal head is too large for the small maternal pelvic canal, also can occur. Uterine torsion is also a cause of obstruction. Malpresentation is the most common fetal cause of obstruction. Fetal oversize or congenital deformities causing large abnormal shape may also cause obstruction. Small litter size predisposes to dystocia in bitches for a variety of reasons. The fetal signals that initiate parturition may be insufficient in very small litters. This may lead to prolonged gestation. A negative correlation between litter size and puppy size exists: the smaller the litter, the larger the individual pup. This may increase the likelihood of obstruction. Conversely, a very large litter may overstretch the uterus and lead to inertia. Litter size has no apparent bearing on the occurrence of dystocia in queens. Fetal death accounts for 1% to 4.5% of dystocia in bitches and queens, respectively. Extreme anxiety reportedly inhibits normal progression of labor.
Early recognition and correction of dystocia is crucial to the successful management and optimal neonatal health. The first things that should be determined are the presence of placental membranes or fetal parts at the vulva, and the presence and character of any vulvar discharge. A partially delivered puppy or kitten needs immediate attention. Breeders should be asked if they have already administered any drugs or performed any obstetric procedures. The following historical findings are indicators of dystocia and reason to recommend that the animal be examined:
A common error made by owners and veterinarians is to delay intervention based on the fact that the dam does not appear to "be in trouble." The fetuses are often severely stressed long before the dam shows clinical signs relating to their demise. The dam should be examined and ultrasound performed to assess fetal viability if the expected due date has arrived and no signs of labor exist, irrespective of a lack of maternal discomfort or illness.
If stage I has not progressed to stage II within 12 hours, the dam should be examined. Exercise often stimulates abdominal contractions. For that reason, some have recommended that the owners walk the bitch up and down the stairs or around the house before loading her in the car for the drive to the veterinary hospital. The onset of stage II of labor is recognized by the return of rectal temperature to normal, the presence of strong abdominal contractions, and the passage of amnionic fluid. The passage of amnionic fluid is an indication of stage II labor, irrespective of obvious abdominal contractions. The first pup should be born within 2 to 3 hours of amnionic fluid. Other findings of concern are the presence of a vulvar discharge, fetal membranes, or a partially delivered fetus. A dark green discharge in bitches or red-brown discharge in queens originates from the placenta. Its presence indicates that at least one placenta has begun to separate. If a pup or kitten has not been delivered within 2 to 4 hours, the dam should be examined. A bright yellow vulvar discharge is meconium. Passage of meconium is indicative of severe fetal stress. It is often associated with fetal aspiration of amnionic fluid and a grave prognosis for neonatal survival. A purulent discharge may be found if uterine infection or fetal maceration exists. Viable fetuses may also still be present.
In dogs neonatal mortality is directly correlated to duration of labor. If delivery is complete within 1 to 4.5 hours of the onset of stage II labor, puppy mortality is about 6%; whereas, neonatal mortality is about 14% after 5 to 24 hours of stage II labor. The outcome for the bitch and the puppies is favorable when the dam is healthy, the fetal heart rates are normal (>200 bpm), when stage I is less than 6 hours in duration, and the duration of stage II is less than 12 hours. When stage II lasts longer than 12 hours but less than 24 hours, the prognosis for puppy survival is poor, although the prognosis for the bitch is still fine. If stage II lasts longer than 24 hours, the puppies are likely to die and morbidity for the bitch is increased. Fetal heart rates less than 150 to 160 bpm or illness in the bitch is also associated with worsening prognosis.
The first step is to examine the perineum for evidence of a partially delivered fetus, which requires immediate attention. There may be a bulge in the perineum dorsal to the vulva, or there may be fetal limbs or tail protruding from the vulva. When it is determined that no partially delivered fetus is present, the complete physical examination of the dam proceeds as usual. Systemic illness in the dam should be pursued as usual for any ill animal. In bitches of adequate size, a digital vaginal exam should be performed to assess for the presence of a fetus in the birth canal. If none is found, the dorsal wall of the vagina should be stroked, because doing so often stimulates abdominal contractions. This procedure has been referred to as "feathering." The cervix is not palpable per vaginum. After assessing maternal health by physical examination, the fetuses are assessed by radiology and ultrasonography. The number, size, shape, location, posture, and presentation of any remaining fetuses are often best determined by radiographs. Ultrasonography is ideal for assessment of fetal viability on the basis of heart rate and fetal movement.
Fetal movement and heart rates are decreased as a result of stress and hypoxemia. In fetal pups, heart rates below normal (>180 bpm) are associated with poor neonatal survival. It has been shown that heart rates <150 to 160 bpm indicate fetal stress. When heart rates are less than 130 bpm, there is poor survival unless pups are delivered within 1 to 2 hours. There is high neonatal mortality among pups with fetal heart rates less than 100 bpm unless they are immediately delivered. Lack of fetal movement, irrespective of heart rate, is also a poor prognostic indicator.
When it has been determined that an "overdue" bitch is healthy and the fetuses are healthy (as determined by the presence of fetal movement and normal heart rates), serum concentrations of progesterone could be determined. This would be especially helpful in situations where information by which the actual length of gestation might be calculated is lacking. The finding of progesterone that is greater than 3 ng/ml (9 nmol/L) in a bitch would indicate that the pregnancy has not yet reached full term. Intervention should be delayed and watchful waiting should continue for several hours. If 24 hours pass with no progression of labor, all parameters should be reassessed. Animals in stage I of labor are expected to progress to stage II in less than 12 hours. When that does not happen, watchful waiting no longer applies, nor does it apply to dams already in stage II of labor.
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The type of treatment is dictated by the presence or absence of obstruction and by the health of the dam and fetuses. In addition to maternal survival, the goal of managing dystocia is to achieve puppy and kitten survival beyond the most critical first week of life. A partially delivered fetus should be delivered within 10 minutes. If obstruction or serious fetal compromise exists, Caesarean section is indicated without delay. If no obstruction exists, medical management may be attempted in healthy dams with no signs of fetal stress.
In situations were the dam and the fetuses are healthy, and no obstruction exists, medical management of dystocia can be considered. The goal of medical management is to re-establish a normal labor pattern of uterine contractions. This is done with oxytocin and calcium. Typically, oxytocin increases the frequency of uterine contractions and calcium increases the strength. High doses and/or frequent administration of oxytocin are contraindicated because they cause sustained uterine contractions that delay the expulsion of fetuses and compromise placental blood flow. Current recommendations are to administer small doses, 0.25 to 4.0 U per dog, intramuscularly (IM). Labor should progress (i.e., straining begins) within 30 minutes and a pup should soon be delivered. If so, the clinician may repeat administration of oxytocin as needed to perpetuate normal parturition. Repeated doses should not be administered if a normal labor pattern is not established.
Generally speaking, calcium administration increases the strength of uterine contractions even in the absence of documented hypocalcemia. For this reason, some have recommended the routine administration of calcium gluconate in the management of non-obstructive. Calcium gluconate, 0.2 ml/kg or less, or 1 to 5 ml/dog, is administered subcutaneously (SC) or intravenously (IV), depending on the preparation and the label directions. Some preparations are too irritating to be administered by routes other than IV. If the IV route is chosen, calcium is administered slowly (1 ml/min), while ausculting the heart. Administration should be immediately discontinued if bradycardia or dysrhythmia occurs. Higher doses or bolus IV administration of Ca gluconate should be reserved for animals with documented clinical signs or laboratory evidence of hypocalcemia. When medical management fails to initiate a normal labor pattern, Caesarean section should be performed.
Caesarean section is indicated, without delay, in the following circumstances: obstruction, such as fetal oversize, fetal malposition, or uterine torsion; fetal compromise exists; medical management with calcium/oxytocin administration has failed; continued pregnancy or labor might be harmful to the dam; or maternal illness already exists.
Embryonic and fetal death can result from maternal disorders, fetal disorders or placental disorders. Queens and bitches often lose one or more fetuses and yet carry the rest of the litter to term and deliver normal healthy puppies or kittens. Anything that adversely affects the health of the dam, and medications used to treat her, have the potential to adversely affect the pregnancy. Other than a disorder that causes overt clinical illness in the dam, the signs associated with fetal death depend primarily on the stage of gestation at which the loss occurs.
When early embryonic death occurs, there are no clinical signs of the bitch having been pregnant. Therefore, she is likely to be presented for (apparent) failure to conceive rather than for pregnancy loss. In queens, having been induced to ovulate by the fertile mating, early embryonic death will be reflected by a prolonged interestrual interval of 30 to 50 days, rather than the usual non-ovulatory cycles every 14-21 days. Pregnancy loss has no effect on the canine interestrual interval. Usually there are no physical signs, such as vulvar discharge, when embryonic death occurs during the first 30 days of gestation in bitches and queens. Resorption occurs. When fetal death occurs after about day 30 of pregnancy, uterine contents are passed (abortion). The first clinical sign of abortion is usually a blood-tinged vulvar discharge. The character of the discharge is variable, according to the underlying cause of the abortion. The quantity is variable from scant to substantial. The later in gestation fetal death occurs, the more obvious it becomes that fetal parts are being expelled.
Infectious diseases are an important cause of pregnancy loss in dogs and cats. They can cause early embryonic death, resorption or abortion through their effects on the dam, the fetus, or the placenta. Other than interrupting pregnancy, many of these pathogens cause minimal clinical signs of maternal illness. Bacteria reported to cause fetal death and abortion in bitches include Brucella canis, Escherichia coli, β-hemolytic Streptococcus, Leptospira, Campylobacter, Salmonella, Mycoplasma spp. and Brucella abortus. Experimental infection with Toxoplasma gondii has also been found to cause abortion in bitches and queens. Viral agents are the most commonly reported infectious cause of abortion in queens. Calici virus is one of the most important. In addition to calici and herpes viruses, parvo virus (panleukopenia), feline leukemia virus, feline immunodeficiency virus and feline infectious peritonitis have been implicated as causes of abortion in cats. Canine distemper is reported to cause bitches to abort.
Apparent luteal insufficiency is discussed as a cause of resorption and abortion, but it is rarely documented in bitches or queens. Certain drugs that may be used to treat or prevent maternal illness are also known to be toxic to pregnant females, to be teratogenic, to cause fetal death, or to cause abortion. Nutritional imbalances can cause pregnancy loss. Fetal anomalies and chromosomal aberrations are cause abortion. Most congenital fetal anomalies have no identifiable cause. Some are known to be heritable. Some are caused by environmental factors such as exposure to teratogens. When normal-appearing, full-term puppies or kittens are stillborn, the most likely cause is fetal distress during parturition. Subsequent pregnancies and labor should be monitored more closely for signs of fetal stress.
The diagnostic efforts are directed toward finding the cause of resorption and abortion so that (1) the dam and any remaining viable fetuses can be treated properly, (2) the problem can be avoided during the subsequent pregnancies of this particular female, and (3) the rest of the colony can be protected from similar occurrences. The dam should be thoroughly examined for signs of illness and for the presence of remaining fetuses. Bitches and queens may abort part of a litter and carry the rest to term. Therapy for the aborting female is supportive and symptomatic, unless a cause can be found. If viable fetuses remain, the pregnancy can be allowed to continue. If not, any remaining contents of the uterus should be removed by ovariohysterectomy or through the administration of ecbolic agents.
From: Johnson CA, Reproductive System Disorders. In: Nelson RW and Couto CG (eds) Small Animal Internal Medicine 4th edition. St. Louis, Elsevier.