That wouldn't really work unless there's a LOT of stuff going on in the woman's life and she's too busy to notice her periods have stopped. I know that not every woman tracks their periods, but 6 weeks is a long enough time that it would still be noticed. Especially since on average, a healthy woman has a period every 15-28 days, with 18-21 being most common (I know most web sources give slightly different amounts, usually just saying exactly 21 days, but I got this from a very well researched book on sex that I had to read for college so it's the amount I'm referencing. Plus I'm a woman myself, I track my periods, and I can say for sure that not all healthy women fall into the idealized 21 day model of prediction).