I've been on a 5AR inhibitor for the last seven years, during which time we had our second son and will soon be expecting our third child. I'm using dutasteride now and previously used finasteride. Our older boy who is the one with severe non-verbal autism was conceived and born before I ever used a 5AR inhibitor. Our second son (during whose pregnancy I was using finasteride) is healthy. Research has indicated that there is very little risk associated with using finasteride when your partner is pregnant or trying to become pregnant. A study found that the amount of finasteride in a man's semen that is available for vaginal absorption is extremely small, being around 750 times lower than the minimum concentration that is believed to be able to cause birth defects. I seem to remember reading a similar study for dutasteride too. A pregnant woman should never be in physical contact with finasteride pills, however. There is some evidence that 5AR inhibitors can mildly negatively affect some men's fertility, though that was clearly not a problem for me personally.
All in all, it is a personal decision whether or not you choose to continue using finasteride when having a child. I chose to stay on treatment while having a child, but that doesn't necessarily mean you should too. It is important to decide what you feel is best for yourself.