When a woman gets pregnant in her bedroom, the reproductive equation is very simple.
She ovulates a single egg from a mature follicle in her ovary , which gets fertilized by a single sperm, which forms a single embryo, which then becomes a baby.
So the equation is : follicle -> egg + sperm = embryo -> baby.
Of course, natural reproductive efficiency is not great, and fecundity for a young fertile woman is only about 20%, in one cycle.
This means that most women will not get pregnant in most cycles, even though she has sex regularly. Now this means that the equation breaks down - either because she did not grow a follicle ( anovulation); or didn't release an egg ; or the sperm didn't manage to fertilize the egg ; or the embryo didn't implant.
Often, for fertile women, it's the failure of embryo implantation which is the reason they don't get pregnant every month they have sex. This is the weak link in the reproductive equation, and is because most embryos have genetic defects - whether these are created in vivo, or in vitro !
IVF patients need to remember that a follicle is not equal to an egg; and egg is not equal to an embryo; and an embryo is not equal to a baby ! Yes, we can help them to grow follicles, but these don't always translate into babies, because of human biological reproductive inefficiency. Many follicles don't contain eggs; many eggs don't fertilise; and most embryos don't implant.
What to find an IVF clinic which respects your time and intelligence ?