Weird how antivaxxers use this obscure bit of knowledge to get scared about similarity of covid S-protein to syncytin and immune response to covid vaccine (why not covid itself?) making pregnancy harder or impossible.
Please do not mistake this comment as antivaxx nonsense, the article linked discredits both the theory and the scientists who started it all.
I couldn't find anything stronger than "german doctors say" which means nothing.
That's all there is to it.