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.
Chemical pregnancy. The most common explanation for a false positive is that you really were pregnant when you took the test. Some women can get a positive pregnancy test and then three days after their period is due, they have a really heavy period, says Lanalee Araba Sam, M.D., an ob-gyn in Fort Lauderdale. Really what they've had is an early miscarriage called a chemical pregnancy, and a lot of people call that a false positive.