Case information:
You are presented with a 3 year old intact female Tibetan spaniel who was accidentally bred by her son about 6 weeks ago. The owners are interested in pregnancy termination. A radiograph and abdominal ultrasound image are below.
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Question:
Does the history match what is visible on the abdominal radiograph and ultrasound images?
Answer:
Yes. Scant mineralized foci are visible in the bitch's uterus on the radiograph. Mineralized foci first become visible 42-45 days from breeding; discernible fetal skeletons are not visible until later. The bright echo within the dark ball of fluid visible on ultrasound is an early mineralized fetus.
Question:
What options exist for pregnancy termination? What should the owner expect to see with each technique?
Answer:
Ovariohysterectomy can be performed at any time. There are no studies defining optimal times during pregnancy for performance of ovariohysterectomy for pregnancy termination but many veterinarians will have a personal limit, set to recognize the increased difficulty and personal displeasure in spaying a heavily pregnant bitch.
Estradiol cypionate is sometimes called the mismate shot. Estradiol cypionate works by decreasing movement of the egg through the uterine tube and into the uterus and so must be used after ovulation has occurred. Estrogen compounds should not be given to bitches in diestrus as this is associated with increase incidence of pyometra. Estradiol cypionate is not so much a pregnancy termination agent as it is a contraceptive and cannot be used in this bitch, who is in advanced pregnancy.
Prostaglandin F2alpha works by lysing corpora lutea, with subsequent decline in progesterone, and by causing uterine contractions, which physically break down and expel the pregnancy. Prostaglandins are effective anytime after the 5th day of diestrus in bitches and so can be used in late pregnancy. It is administered as a series of infections over 4-7 days. If prostaglandin is administered before about 40 days from breeding, all the pups are resorbed. From 40 to about 50 days, fluid and some tissues will be passed vaginally. If administered after 50 days of gestation, obvious fetuses may be passed and after 55 days, the fetuses may be viable. Side-effects of prostaglandin use include hypersalivation, vomiting and diarrhea. These side-effects usually are short-lived and decrease in severity and frequency over the series of injections.
Dexamethasone also acts by decreasing serum progesterone concentration. It can be used after mid-gestation and is administered orally for 10 days, making it an inexpensive and convenient option for dog owners. Pregnancy termination does not occur until late in the 10-day treatment and is associated with passage of dark, tarry discharge or obvious fetal tissues. The primary side-effect is polyuria / polydipsia, which subsides with conclusion of therapy. This drug is reported to be 80% effective for pregnancy termination; pups born after therapy of the bitch are normal.
Prolactin inhibitors include the human drug bromocriptine and the veterinary product cabergoline. Prolactin is necessary for support of the corpora lutea so administration of prolactin inhibitors is associated with luteolysis and a subsequent decline in progesterone. Some practitioners use a combination of a prolactin inhibitor and a prostaglandin to decrease side-effects and cost.