Most moms carrying twins go into labor at 36 to 37 weeks, as opposed to 40 in a single pregnancy, Al-Khan says, and some may go even earlier. Generally, if the twins are born after 34 weeks, there should not be a major concern, but a premature baby is still a premature baby, he says.
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.
In some dogs, a false pregnancy, or pseudocyesis, can occur 6 to 12 weeks after a heat cycle and is caused by hormones. Symptoms usually last for about 3 to 4 weeks and include vaginal discharge, weight gain and nesting behavior, like shredding blankets.