So...I think you CAN accidentally get pregnant. Birth control doesn't work 100% of the time. And when women aren't taught about how to use birth control and how their own bodies work, but are expected to be responsible for all the birth control that goes on in the relationship (despite the fact that there are steps guys can take to contribute), then you end up with accidental pregnancies.
In this specific case, I'd bet money almost all noblewomen who were consorts understood birth control of some sort, because their status and politics were directly tied to bearing children. That being said, this sounds very interesting.