Most people who believe life begins at conception are opposed to IVF because typically more embryos are fertilized than are implanted. The ones that are not implanted are destroyed, frozen long term, or on occasion used for embryonic stem cell research. For someone who is pro-life having embryos frozen forever should be a little disturbing, but the other two alternatives should be considered murder if that person is consistent.
This is not including the Christians who are opposed to this type of treatment because they think that any medical interference to either prevent or induce pregnancy is displaying a lack of faith by failure to rely on God.
What you state may be true, that, however, does not make praying for a successful outcome a sin.