Im anot sure that catholics do have higher fertility than protestants. Perhaps they used to due to earlier industrialisation in protestant dominated areas? Today Protestan/atheist Sweden has a higher fertility rate than catholic/atheist Italy.
There are numerous studies shown on this, and it's even a stereotype that Catholic families have huge numbers of children (overlaps with Irish stereotypes, granted). Catholic countries in Europe have a higher fertility rate then Protestants. In the US, Catholics historically had a higher fertility rate then Protestants.
Sweden I'm assuming is because of the recent immigrant population. Muslim immigrants tend to have a higher fertility rate than the locals. I'm not sure how high the fertility rate is for Christian immigrants (there is a sizable Aramaic-speaking population in Sweden, for instance).
Maybe ATL the orphanges and foster system in Romania can have less reason for infamy.
Romanian orphanages are an extreme example, being mainly a result of the economic conditions in the 80s in Romania combined with the government natalist policies, but they're still likely to be horrible (but not as internationally infamous) due to lack of government money (the government has many other things to spend money on, and not enough money to budget) and the ever-present corruption.
Maybe some sort of "atheist religion" could form in a communist country? What about a state cult? It seems that the communist beliefs that these Warsaw pact countries held, had some resemblance to religion.
https://en.wikipedia.org/wiki/God-Building
Communism can be pretty similar to a religion, and indeed some communists have taken it to the levels that where you really can call it a religion. This is similar to the French Revolution's religious aspects like the Cult of Reason. The problem is that Lenin himself condemned the God-Building movement and thus the movement had died well before WWII. Naturally, the religious community of Eastern Europe condemned the movement, since it's pretty akin to what the Bible warns about false prophets.