I thought the contraceptive doesn't prevent the pregnancy but just causes the body to menstruate regardless. So she might have been pregnant many times but this time it wasn't terminated by mensuration? (I'm certainly not very confident in my understanding.)
> The birth control pill works by stopping sperm from joining with an egg. When sperm joins with an egg it’s called fertilization.
> The hormones in the pill safely stop ovulation. No ovulation means there’s no egg for sperm to fertilize, so pregnancy can’t happen.
> The pill’s hormones also thicken the mucus on the cervix. This thicker cervical mucus blocks sperm so it can’t swim to an egg — kind of like a sticky security guard.
This is correct with the additional caveat that the pill also thins the uterine lining, making it difficult for the embryo to implant in the rare event of fertilization. So for people concerned about avoiding an abortion, the pill rarely, but not never, results in abortion.
