Miscarriage in Dogs

By Tammy Hunter, DVM; Catherine Barnette, DVM

What is miscarriage?

Miscarriage refers to the death of a fetus during pregnancy. This fetal death can occur at any time during pregnancy, though the signs of miscarriage vary depending on the stage at which it occurs.

Some miscarriages occur early, during the first half of pregnancy (before 45 days). In these cases, the embryo is often reabsorbed into the body, and the miscarriage may go completely undetected. Sometimes, one or more puppies in the litter may be miscarried and resorbed, while other puppies in the litter go on to be born normally.

"Sometimes, one or more puppies in the litter may be miscarried and resorbed, while other puppies in the litter go on to be born normally."

Miscarriages may also occur later in pregnancy and may result in various outcomes. Puppies may be passed stillborn, either before their due date or on their due date. In some cases, a deceased fetus may become mummified within the uterus. Mummification occurs when the body creates a protective membrane around the fetus, allowing it to remain encased and walled off within the uterus. In many cases, mummification does not threaten the female; in some situations, however, an infection may occur.

What causes miscarriage?

Infection is a common cause of miscarriage in dogs. These infections can be bacterial, viral, or parasitic. Brucella Canis is a species of bacteria that is commonly associated with late-term miscarriage in clinically healthy dogs. These bacteria are transferred by contact with infected fluids, which may occur when a female is bred with an infected male or when a female comes into contact with the birth fluids of an infected female.

Other bacteria associated with miscarriage include E. coli, Pasteurella, Pseudomonas, and Staphylococcus. However, it is often difficult to determine whether bacterial infection caused a miscarriage because these bacteria may be present in healthy females and those females that miscarry.

Parasites, such as Neospora caninum and Toxoplasma gondii, are also associated with miscarriage, as is canine herpesvirus.

Hormonal shifts or abnormalities may also cause miscarriages. Progesterone is the hormone responsible for maintaining pregnancy in the dog; low levels of this hormone can lead to miscarriage. In some cases, these low progesterone levels can be caused by medications (such as in the case of medically induced abortions). Maternal and placental factors may lead to abnormal hormone levels, resulting in miscarriage.

What are the clinical signs of miscarriage?

In many cases, there are no visible signs of miscarriage. Early miscarriages typically result in embryo resorption with no outwardly visible signs and are only detected if the pregnancy was confirmed on an early ultrasound and a later ultrasound shows no viable pregnancy. Later-term miscarriages may be associated with clinical signs but may also be asymptomatic. Abnormal vaginal discharge (brown, green, black, or pus-colored) at any time during pregnancy, abdominal pain, and fever are all potential signs of miscarriage or infection. Additionally, some pets experiencing a miscarriage will have contractions and deliver stillborn puppies.

How is miscarriage diagnosed?

If miscarriage is suspected, ultrasound is used to assess the pregnancy and determine whether the fetuses are alive. Progesterone level monitoring can also benefit pregnancy monitoring; abnormal progesterone levels may indicate a failing pregnancy. After a miscarriage, testing the mother and the fetus may be recommended to look for infectious causes. Blood tests on the mother, cultures of vaginal fluids, and histopathology (microscopic examination) of the fetus may determine the reason for the miscarriage.

"If miscarriage is suspected, ultrasound is used to assess the pregnancy and determine whether the fetuses are alive."

Finding a cause for the miscarriage, especially if that cause is a treatable condition, may improve outcomes in future pregnancies.

How is miscarriage treated or prevented?

A dog developing a fever during pregnancy may indicate an infection. Infections are typically treated with intravenous (IV) fluids and injectable antibiotics. This may prevent miscarriage or, if a miscarriage has already occurred, may prevent more severe medical complications with the mother.

If hormonal imbalances are suspected, a progesterone supplement may be recommended. This medication is given daily until shortly before the expected due date to help maintain appropriate hormone levels to support pregnancy. This medication requires careful monitoring to prevent complications.

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