Joan(/Jen/whatever) was never introduced to Sherlock and as such has slipped down a nasty slope of drinking a bit to much in strange bars, perhaps not full on addiction just yet but definitely an unhealthy relationship with alcohol
Sherlock saved himself from the cabbie (he guessed right) but things happened much the same way with The Woman and now after realising he doesn't like Moriarty's nikcname for him, nor the way that Irene had said it Sherlock decides it time to have sex.
Of course he's Sherlock so he decides to go to a bar and pick up the woman least likely to remember if he makes a mistake, yet sober enough to be able to give consent. Joan fits that description, they have sex and Sherlock is surprised by how interesting he finds his partners responses but afterwards they part ways.
Two months later Joan shows up again the condom failed she's pregnant, she figured Sherlock would like to know.
Cue slightly uncertain Sherlock who insists Joan move in, BAMF!Joan who's gotten her life sort of back on track since that night and yet decides to humor him since the kid is his and overprotective!Mycroft (first of Sherlock since the last woman he showed an interest in didn't end to well and once he's figured out why Joan is living there of her and the baby as well)
Short: Sherlock knocks up Fem!John during a one night stand and insists she moves in.
Fem!John
Sherlock saved himself from the cabbie (he guessed right) but things happened much the same way with The Woman and now after realising he doesn't like Moriarty's nikcname for him, nor the way that Irene had said it Sherlock decides it time to have sex.
Of course he's Sherlock so he decides to go to a bar and pick up the woman least likely to remember if he makes a mistake, yet sober enough to be able to give consent. Joan fits that description, they have sex and Sherlock is surprised by how interesting he finds his partners responses but afterwards they part ways.
Two months later Joan shows up again the condom failed she's pregnant, she figured Sherlock would like to know.
Cue slightly uncertain Sherlock who insists Joan move in, BAMF!Joan who's gotten her life sort of back on track since that night and yet decides to humor him since the kid is his and overprotective!Mycroft (first of Sherlock since the last woman he showed an interest in didn't end to well and once he's figured out why Joan is living there of her and the baby as well)
Short: Sherlock knocks up Fem!John during a one night stand and insists she moves in.