Could this question be included in the FAQ?
Merck considers it to be safe to use finasteride while conceiving. As far as I remember, dosages hundreds of times the size have been tested in monkeys and found no indication the finasteride was affecting the semen. On the other side, I remember something about several incidents where it was suspected that finasteride could have caused some disorder, but that a causative relationship wasn't provable.
This has been discussed before on these forums. (Could this question be included in the FAQ?)