Welll...that's changing.
Russian women are still a) mostly very attractive, and b) a lot more religious then Russian males. Orthodox Christianity is making a comeback even though the government still wants to control it (some things never change in Russia). So Russian women want to have children and raise them in their church. I know enough of them to believe this; I even know Russian Evangelicals. Once the two decade long party known as "Thank God Communism is OVER!" gets over (and it's dying down now), they'll get back to making Russian babies and trying to resurrect their society after the 70 year disaster.
Belarus...very different because they still have Lukashenko, haven't let go of the past. But eventually that won't matter...all around them the world will change, and even he won't be able to do anything about it.
Ukraine wants to be part of the West, but unfortunately the ethnic Russians have a hard time with that. But the Mommies want good stuff for their babies and they won't give a damn what the nostalgics think, I know a number of them and they love kids and being Mothers, they will not be stopped by retro Bolshevikii. Religious people too.
The Baltics? They are not part of the Russian East and no Tsar was ever able to make them. Once the Russian army was gone they bolted politically and spiritually right back to being the Northern Europeans they are. Don't worry, they like themselves and their kids, they'll be back. My Estonian stepgrandmother told me so!
I hope you’re right about a general trend toward a higher birthrate, rather than isolated data points. It’s not unusual for very religious families in the US to have many children, but there aren’t enough, as a percentage of the population, to affect the average very much.