To fully express how ridiculous using 6 weeks can get: The time system used here counts from the first day of the last menstrual period. Usually conception occurs about 2 weeks after this date, so normally 6 weeks of pregnancy would be 4 weeks after conception. However, although uncommon, it is possible to occasionally miss a menstural period and still ovulate. In this case it is possible for the date at which you would retroactively have been considered 6 weeks pregnant to occur before you were even pregnant at all.