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.
Blood or protein in the urine may cause false-positive pregnancy results. Urine hCG tests may give a false-negative result if the urine is too diluted or if testing is done too soon in the pregnancy. Certain drugs such as diuretics and promethazine (an antihistamine) may cause false-negative urine results.