IF YOU LIKE MARY WATSON OR OTHERWISE SUPPORT THE WATSON MARRIAGE, SCROLL PAST THIS POST
Okay, so I just realized something. Mary knew who she was dealing with when Sherlock came back. She read the blog probably before the whole “I don’t shave for Sherlock Holmes” bit, but definitely during it. She knew secrets don’t stay secret around the man, and she’d need a plan for after hers came out.
Hence the pregnancy. Face it, if you’re in a committed relationship with a man, having regular or semi-regular sex, you’re on birth control. Heck, if they can afford it, many women only rarely having sex usually stay on the pill for an extra level of protection. Add in condoms, which I’m sure a man with the sexual experience and caretaker qualities John has in spades, and you’ll find a situation in which someone would have to try to become pregnant. Yes, it’s possible for two levels of protection to fail, but the likelihood of it happening is slim to none (unless my math betrays me, it’s .72%. Less than a percent, people).
So, let’s return to the timeline. Mary and John are getting married, and Sherlock and John are friends once again. Mary knows John’s chances of figuring her out rise daily, so she’s get to figure out how to make him stay. And isn’t a baby the perfect one? John can’t walk away from his own child, can he? So Mary stops taking the pill, perhaps even convinces John not to use a condom once or tampers with the ones he normally uses.
In my mind, I think she expected for her secret to come out long before the wedding, or much shorter after it. After all, she did say the Sherlock was slower than usual. But boom-bada-boom, baby Watson comes into the picture, and how could John, a caretaker by nature, stay away from his pregnant wife for too long?
She manipulated him into conception, and doubtlessly would have coerced him into marrying her. If that doesn’t reek of villain potential, I don’t know what would.