Page 990 - Small Animal Internal Medicine, 6th Edition

962 PART VIII Reproductive System Disorders

laparotomy and lavage of the abdomen are indicated. Inspec- hyperthyroidism—unlikely conditions in breeding bitches or
tion of the vagina (endoscopically) and uterus (grossly) for queens. The main contraindication to tocolytic therapy in
VetBooks.ir perforation should be carefully performed. This syndrome veterinary medicine is undetected uterine, fetal, or placen-
tal pathology, making forced maintenance of the pregnancy
has high morbidity and mortality for the bitch.
PREGNANCY LOSS problematic for the dam.
Dams with historical late-term loss of pregnancy with no
The prepartum period is defined as 9 weeks before term. apparent pathology should be prospectively evaluated for
Pregnancy loss most commonly occurs with idiopathic pre- premature myometrial activity midgestation, using uterine
mature labor, infectious causes, or significant maternal monitoring, for example, tocodynamometry (Healthdyne)
disease or trauma. (Fig. 55.8, A, 55.8, B). Elaboration of prostaglandins from the
endometrium and placenta associated with premature myo-
IDIOPATHIC PRETERM LABOR metrial activity can result secondarily in luteolysis. Prema-
Late-term gestational loss attributed to preterm or prema- ture uterine activity endangering fetal survival can be
ture labor occurs in both bitches and queens. Both hypolu- identified before significant luteolysis occurs, and interven-
teoidism (inadequate production of progesterone to maintain tion is indicated if the pregnancy is otherwise normal. Phar-
pregnancy) and inappropriate uterine activity (myometrial macologic intervention to decrease myometrial activity is
irritability) accompanied by cervical changes (softening) indicated with tocolytic agents. Terbutaline (Brethine [Ciba
have been implicated in the pathophysiology of preterm Geigy]) at 0.03 mg/kg PO q8h has been used to suppress
birth in veterinary medicine, but the syndrome is not well uterine contractility in bitches and queens with historical
understood or adequately researched. Premature labor is preterm loss of otherwise normal pregnancies (Figs. 55.9, A,
defined as uterine activity and cervical changes leading to 55.9, B, 55.10). The dose is ideally titrated to effect using
the loss of pregnancy via resorption or abortion before term tocodynamometry. Diltiazem (Cardizem [Bioval Laborato-
for which no metabolic, infectious, congenital, traumatic, or ries]) at 0.5 mg/kg PO q8h (canine) and 1.5-2.5 mg/kg PO
toxic cause is identified. Progesterone levels can be normal q8h (feline) can be used if response to terbutaline is inade-
for pregnancy (5-90 ng/mL) when increased myometrial quate. Therapy is discontinued 24 to 48 hours before term to
contractility is first detected. Premature deliveries occur allow labor to proceed. In the author’s experience, poor
when progesterone levels are less than 2.0 ng/mL. Premature quality labor requiring cesarean section is common postto-
labor is often a retrospective diagnosis achieved after thor- colytic therapy. An elective cesarean section should be dis-
ough evaluation of the dam and stillborn fetuses has been cussed with clients.
performed. This evaluation should include metabolic screen- Canine and feline pregnancy maintenance requires serum
ing of the dam for systemic disease, infectious disease progesterone levels of greater than 2.0 ng/mL. Serum pro-
(brucellosis) evaluation, histopathology and microbiologic gesterone levels during pregnancy normally range widely
evaluation of expelled fetuses and placentae, and review of from 5-15 to 90 ng/mL, declining gradually during the latter
kennel/cattery husbandry, including nutrition, medications, half of gestation and falling abruptly at term to <2.0 ng/
and environmental factors. All results are normal or nega- mL (usually the day before or the day of parturition). Pro-
tive. Dams experiencing premature myometrial activity in gesterone promotes development of endometrial glandular
one pregnancy might or might not exhibit it during subse- tissue, inhibits myometrial contractility (causes relaxation of
quent pregnancies, but the syndrome can be a chronic cause myometrial smooth muscle), blocks the action of oxytocin,
of failure to successfully reproduce. In human medicine, inhibits formation of gap junctions, and inhibits leukocyte
preterm birth complicates 10% to 12% of human pregnan- function in the uterus. In several species, local changes in
cies, but it accounts for 80% of fetal morbidity and mortality progesterone level or the ratio of progesterone to estrogen
(Dyson et al., 1998). Women with histories of preterm deliv- in the placenta, decidua, or fetal membranes is important
eries appear to be at risk for the same in subsequent in the initiation of labor. Progesterone antagonists admin-
pregnancies. istered at term can result in an increased rate of spontane-
Tocolytic therapy inhibits myometrial contractility and ous abortion. In the bitch, the corpora lutea are the sole
is indicated in the management of premature labor when source of progesterone, whereas in the queen, placental pro-
no contributory pathology is identified. Contraindications gesterone production occurs in the latter half of gestation.
to tocolytic therapy in women include severe preeclampsia, Canine luteal function is autonomous early in pregnancy
placental abruption, intrauterine infection, lethal congenital but supported by luteotrophic hormones (LH and prolac-
or chromosomal abnormalities, advanced cervical dila- tin) after the second week of gestation. Hypoluteiodism,
tion, and evidence of fetal compromise or placental insuffi- primary luteal failure occurring before term gestation, is a
ciency. Tocolytic agents inhibit myometrial contractions and potential but not yet documented cause of late-term abor-
include beta mimetics (terbutaline, ritodrine), magnesium tion in otherwise normal bitches and queens. It has been
sulfate, calcium channel blockers, and prostaglandin syn- documented that the induction of abortion in a normal but
thetase inhibitors (indomethacin, ketorolac, sulindac). Con- undesired pregnancy requires a reduction of plasma proges-
traindications to beta mimetics in women include maternal terone levels to less than 2.0 ng/mL. The diagnosis of gesta-
cardiac arrhythmias, poorly controlled diabetes mellitus, and tional loss caused by premature luteolysis/luteal insufficiency