False pregnancy,
phantom pregnancy, or
hysterical pregnancy— officially called
pseudocyesis in humans and
pseudopregnancy in other mammals—is the appearance of clinical or subclinical signs and symptoms associated with
pregnancy when the organism is not actually pregnant. Clinically, false pregnancy is most common in veterinary medicine (particularly in dogs and mice). False pregnancy in humans is less common, and may sometimes be purely psychological. It is generally believed that false pregnancy is caused by changes in the
endocrine system of the body, leading to the secretion of hormones that cause physical changes similar to those during pregnancy. Some men experience the same illnesses as a woman would experience while pregnant when their partner is pregnant (see
Couvade syndrome), possibly caused by pheromones that increase estrogen, prolactin, and cortisol levels.