Female dogs can sometimes experience pregnancy-like symptoms while not actually being physically pregnant. This occurs following an estrous cycle, which is sometimes referred to as a dog “going into heat.” This condition is known by many names, including false pregnancy, hyperluteodism, pseudocyesis or pseudo-pregnancy. Typically caused by a hormone imbalance, this condition presents itself in almost all female mammals.

After a female dog enters puberty, she will experience regular estrous cycles which are interrupted by pregnancies. At the beginning of a normal estrous cycle, the female dog’s vulva will swell and she will experience a bloody discharge from her cervix for a period of four to fourteen days.

The bloody discharge will continue as the ovaries prepare to release eggs. As the eggs are released, the discharge changes to a straw color. If a dog breeds at this time, fertilization may occur. The fertility period lasts for the same four to fourteen days as the bleeding, although the average is ten days.

If fertilization does not occur, the female’s body will return to normal, the vulva will return to normal size and discharge will cease. If fertilization occurs, the ovarian follicles responsible for releasing eggs will begin to release a hormone called progesterone which is necessary for normal pregnancy development. During this process the ovarian follicles are referred to as corpora lutea, if no fertilization occurs, these corpora lutea will revert and cease production of progesterone.

During a false pregnancy, the ovarian follicles continue to produce pregnancy levels of progesterone, even though there are not fertilized eggs. This surplus of hormones will trigger other pregnancy symptoms in a dog, both physical and psychological. The actual biological processes involved are much too detailed to address in an article of this length, so this is a simplified explanation.

Symptoms of False Pregnancy

While present in all mammals, false pregnancy is most prevalent in dogs and mice. The condition presents itself as mimicking all signs of a normal pregnancy, including false positives on typical pregnancy tests. During the discovery period, usually one and a half to three months following an estrous cycle, a false pregnancy is indistinguishable from and actual pregnancy.

Symptoms may vary from one dog to another, but the typical symptomology will include swollen mammary glands that may produce milk or milky discharge, lethargy, increased moodiness and aggression, weight gain, and changes in patterns of eating and sleeping. Some dogs may protectively carry around a toy as they would carry a newborn puppy. Pregnancy symptoms are usually fairly easy for an observant owner to notice.

Less commonly, a dog may run a slight fever, lose her appetite or experience digestive upset, including vomiting and diarrhea. The symptoms of a false pregnancy are, by its very name, exactly the same as an actual physical pregnancy. Consulting with a vet is the only way to truly differentiate between false pregnancy and actual pregnancy in the early stages, although an actual pregnancy will be obvious if it ends in puppies.