Mar Vista Animal Medical Center

3850 Grand View Blvd.
Los Angeles, CA 90066





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Sometimes nature takes an unwanted course. Accidents happen. Maybe you kept putting off scheduling your female pet’s spay surgery and before you knew it, she was in heat. Perhaps there was an especially industrious male in the neighborhood. Maybe your newly adopted female pet was assumed to have already been spayed and, to your surprise, she wasn’t.

Accidents happen.

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The situation described above is called "mismating." Sometimes the actual deed is witnessed. Sometimes the pregnancy is discovered midterm. One's natural tendency may be to see if the thing can be undone right away before it gets too far but, unfortunately, hormonal drugs that can accomplish this carry an unacceptable rate of side effects. There is no safe "morning after" treatment (see below). The best choice is to wait until pregnancy is confirmed and leave the decisions until that time.

Your pet dog or cat can be tested for pregnancy with a simple blood test, similar to a home pregnancy test, after approximately 30 days of pregnancy. The test is called a "Witness Relaxin test" and detects one of the hormones of pregnancy.





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This will be more work than you might think. Your pet will most likely be able to manage the birth and early care of the babies but you will be in charge of finding homes for the offspring as well as mom’s prenatal care. You will need to know what are signs of trouble during labor and how to care for your pet in pregnancy. We have areas up on both these subjects:

Please consider before allowing this birth that there is an incredible pet over-population problem. In our area some of the city shelters are euthanizing over 100 dogs DAILY. We need more homes and less animals to solve this problem. This is your opportunity to be part of the solution.



The spay surgery involves removal of the uterus and ovaries. If the uterus is gravid (i.e. carrying developing young), the developing embryos are removed along with the uterus and the pregnancy is terminated. Further, the female cannot ever become pregnant again. If one does not intend to breed the female in the future, this is probably the best option.

There is an increased risk to the female when she is spayed during pregnancy versus when she is spayed routinely. The blood vessels of her reproductive tract become huge and more difficult to tie off during pregnancy. The surgery takes longer and there is usually an extra charge for this. Sometimes she must stay an extra day in the hospital or wear a bandage around her belly at home. The surgical scar will be much longer than it would for a routine spay. The risk of excessive bleeding in surgery increases with the size of the dog and the stage of pregnancy.

Discuss the procedure with your veterinarian so that you understand what is involved and what to expect. Ideally, the female should be out of heat but not in advanced pregnancy.



If it is important that the female animal be bred in the future, the pregnancy can be terminated without sterilizing her. This entails the use of medications to end the pregnancy during the second “trimester," about 30-40 days into the pregnancy. Typically, the female is hospitalized for 5-7 days for the procedure and returned to her owner in a non-pregnant state. It is very helpful to know the breeding date as different medications work only during certain stages of pregnancy. Hospitalization is generally needed because some of the medications will be injectable and there will be objectionable vaginal discharge which will be undesirable at home.

The pituitary gland of the pregnant female secretes two important hormones: Prolactin and Luteinizing hormone (affectionately termed “LH”). Both these hormones nourish and sustain an ovarian structure of pregnancy called a “corpus luteum” which in turn secretes progesterone, which is the hormone that directly maintains the pregnancy.

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Medications used typically include something to disrupt prolactin secretion (either cabergoline or bromocriptine) in combination with a prostaglandin (a hormone to induce uterine contractions and directly destroy the corpus luteum). Less cramping and vomiting is associated with cabergoline over bromocriptine but the cost is substantially higher. Cabergoline is only recently available in the U.S.

Another protocol using dexamethasone, a steroid hormone used commonly for an assortment of medical problems, can be used to terminate pregnancy. High doses are used making side effects common (excessive thirst, excessive urination sometimes with incontinence, panting). A typical protocol involves 9-12 days of medication, does not require hospitalization, and involves minimal vaginal discharge if completed by Day 40 of pregnancy. Some experts feel this protocol is not as reliable as combinations of the other medications mentioned while other experts prefer this protocol. The dexamethasone technique appears to be an option for dogs but not cats.

Your veterinarian will likely have a particular protocol that he/she has used before and feels is reliable and comfortable for the pet.

Some sort of pregnancy test after the abortion procedure is a good idea to be sure the procedure was effective. This kind of testing could be another relaxin test, radiographs of the belly, blood progesterone levels, ultrasound or any combination of these.



In older times, one could bring the mismated female dog to the vet for an injection of estrogen within the first few days after the mismating. This treatment is generally not recommended any more as the high doses of estrogen used predisposed the female to a life-threatening uterine infection called "pyometra" (up to 25% incidence in one study). Dangerous bone marrow suppression is also a possibility plus the estrus (and all the unpleasant vaginal discharge and attraction of males) becomes prolonged. This treatment has been deemed too toxic and should not be requested.


Page last updated: 9/2/2021