hi C.,
i had a root canal done just around the time i conceived (i didn't know i was pregnant yet though) so it may have actually been done before conception. that said, once i knew i was pregnant and had to return for follow-up appointments (crown fitting and such) i let my dentist know and he basically said that novacaine is contraindicated in the first trimester of pregnancy. they like to wait until the 2nd, or even 3rd before doing dental work that requires novacaine. because the root was removed from the tooth, the amount of pain from the subsequent visits without novacaine was minimal... just some soreness from the gum being provoked... and i'm extremely sensitive! there were no noticeable effects on my baby, now an energetic and healthy 21 month old.
the other things about dental work during pregnancy is that you're more likely to bleed... clotting time is much longer. be careful with this-- not to lose too much blood.
fyi, for future appointments if you plan to breastfeed: i had to have dental work post-partum too (with a different dentist). i asked him what he thought about novacaine and breastfeeding and he said, "no problem... it might change the taste of your breastmilk but not to worry." well, this didn't make any sense to me... if enough was getting thru into my breastmilk to change the taste then enough was getting thru to potentially effect my baby. i wasn't going to take any chances. so i consulted with 2 pediatricians, one of whom just had a baby herself so she was extra-sensitized to such issues, and both pediatricians advised me to pump and dump. nurse your baby right before you go for the appt. (or pump, to save the good milk) and then 2 hours after you've gotten numbed up pump and toss the milk. hopefully, you won't have to confront this but just in case you do.
have a lovely pregnancy and an even lovelier baby! good luck
K.