Nitrous oxide and fertility/pregnancy

I am TTC and I need to get a crown put on my tooth (I had a root canal done a few months back). My 33% chance day is tomorrow, and my appointment is in a week. Is nitrous oxide (laughing gas) okay to use in the first weeks (the weeks where pregnancy can't even be detected)?   I've heard it either way. Has anyone had dental work with laughing gas in the first month of pregnancy and been fine? I don't want to put my child in danger but I have dental anxiety... I would just put it off till after I had a baby. 
Does laughing gas effect fertility? Are any of you doctors or health care professionals who can tell me? I thought I read that somewhere, but I haven't heard much about it.