Also asking for date of lmp can be a roundabout way of asking a possibly vulnerable patient about the possibility of being pregnant too. There are girls/women who don't know they've been raped either as they're very young and innocent or they've been drug raped inc by current and ex partners. There are sadly some seriously sick bastards out there.
Not all girls/women have regular periods, that can be a symptom for many things other than pregnancy
not all track their periods
times of stress people can both miss their period and not notice they've missed it because they're preoccupied with whatever's stressing them
medications can mess with periods or need to be started at a certain point in the woman's cycle
Patients forget ALL sorts when you're trying to get a history off them especially when they're worried about the reason they're there or the reason they think they're there. Totally normal for patients to forget important meds their on, serious medical conditions (inc diabetes, heart conditions etc) so procedures have developed over the years to try and cover as many bases as possible.
And they lie too. ALL THE TIME sometimes about the most ridiculous things, I once had one lie about having had chicken pox as a child! Why? They didn't want to draw attention to a small scar caused by it, pure vanity, utterly ridiculous!!
But sometimes understandably so eg if they're being asked if they're pregnant in an emergency scenario in the presence of the husband they haven't slept with for 6 months when they know they could be pregnant by the om.
There's a spot on episode of "only fools" where del is experiencing pains and he's worried sick, but when he goes to the Drs & his old GP has moved on, he makes out he's a teetotal, non-smoking, healthy eating fitness guru and because this means the dr can't figure out what's wrong he ends up in hospital, whereupon his previous Gp who knows him and his true lifestyle was able to quickly DX an easily treated minor condition.
"No watchers of House?
"Everybody lies" " yep!!
"This is true of anything a patient might say. Why presume they're lying?" Because so very many DO! And NOT being thorough and careful can have devastating, long lasting even fatal consequences.
"and you would not believe the number of people who discount the possibility or pregnancy purely because they don’t want to be pregnant." Exactly!
"I wonder if they ask lesbians or nuns?" Lesbians and nuns can be victims of rape and have even been known to have sex with men on occasion.