Hold the phone! I've found something that might explain where this has come from:
Cranberry, as well as many other fruits and vegetables, contains significant amounts of salicylic acid, which is an important ingredient in aspirin. Drinking cranberry juice regularly increases the amount of salicylic acid in the body. Salicylic acid can reduce swelling, prevent blood clots, and can have antitumor effects. [
http://www.webmd.com/vitamins-supplements/ingredientmono-958-cranberry.aspx?activeingredientid=958]
I don't know what salicylic acid is (or what else aspirin is made of) so back to google I went:
No studies examine topical salicylic acid in pregnancy. Oral salicylic acid is not associated with an increase in malformations if used during the first trimester, but in late pregnancy has been associated with bleeding, especially intracranial bleeding. [
https://en.wikipedia.org/wiki/Salicylic_acid]
From the look of it, IF cranberry juice had any effect, it would still be fine in the first trimester. You would have to be drinking an awful lot to make a difference I think, but I'm afraid I have no idea whether that would mean three glasses or three litres a day.
Ultimately, as there's nothing mentioned on the NHS website (or anywhere else reputable), I think you're fine with one or two glasses a day, but maybe don't go over that. And speak to someone proper