Well one question is what to do with unused embryos.
They have the potential of life. Is it right to destroy them?
Another would be where multiple embryos are implanted in the hopes of increasing the chance of pregnancy, resulting in selective termination if the result is a multiple pregnancy (afaik not all clinics do this).
The ethics of using an embryo if a parent has died. Even if they gave their permission prior to death is it fair for a child to know they were implanted after their parent had died? Or what about the case where a mother wanted to carry the child of her dead son?
Equally some people might argue is it appropriate to tinker with nature at all?
To be clear I'm not anti IVF and I'm not suggesting I'm pro/anti any of the arguments above but I think it's fair to say it's a process that is not without ethical concerns and has the potential to cross ethical lines by clinics who provide the service if they are not legally constrained by good ethical standards.