My main concern, pregnant or not pregnant, would be which country it is and what do their restrictions look like.
I didn't go to my cousin's wedding back in August, he was getting married in his partner's country (Eastern Europe it that's relevant). One of my grandmothers lives there and I know how lax restrictions are. No one respects social distancing there, restaurants have no maximum capacity, and the wedding was going to be at a hotel which can't enforce any rules if they're hosting a private gathering 
So I didn't want to go to a party where dozens of people would eat and dance on top of each other, wearing no masks. The bride also announced that her wedding photos were not to include anyone wearing a mask and that she wouldn't join the trend of those 'faking they care about their guests and believing Covid is real'.
Had the wedding been in Ireland, where my cousin is from, I would've probably gone. Because as a country, they actually do enforce mask wearing and other rules. Even though my cousin and his now wife are some of the biggest arseholes I've ever met.
20h drive isn't that long, you can spread it over 2-3 days, but won't you be quite uncomfortable by that stage of the pregnancy?
Are you sure you'd be able to cross all the borders with the car? Which ones require negative Covid tests and how long in advance would they need to be taken... it's just not as easy nowadays as loading a couple of suitcases and going for a road trip... 😞