Can you be 45 weeks pregnant?

Not likely: The usual length of pregnancy is approx 38 - 40 weeks. By approx 41 - 42 weeks most ob's would move toward inducing the pregnancy. Going significantly overdue can be risky. Counting from the first day of your last period is the standard way to calculate the pregnancy length.

Probably not really: A normal pregnancy is up to 42 weeks so it is more likely the dates are incorrect. Traditionally we count from the last menstrual period, but that assumes a 28 day cycle and that actual conception is 2 weeks later. When cycles are prolonged that is a bad assumption and conception occurs much later, hence the traditional dating will produce a "45 week" pregnancy.

No, not for us...: No, not for humans. A 45 week human pregnancy means somebody must have calculated the numbers wrong. Interestingly, american bison have 45 week pregnancies, and sometimes horses have 45 week pregnancies, too.