In the past yes, I knew of families who wouldn't buy anything until the baby is born, just in case something went wrong. I haven't heard the pram one before.
the existence of prams can neither help a pregnancy or hinder it (unless of course you leave it in the way and the mum trips over it). However, a lot of people would rather not have the pram before hte baby. I think mostly people do the research and order it to be delivered near of after the due date. As much for the fact they are blooming huge and in the way when you a a huge fat lump
I am sure that every time i walk under a ladder, things go wrong, not pot of paint on head etc, but just normal things in life. broke a mirror once ( or twice) and am convinced that i had the 7 years bad luck. I stayed in a haunted hotel and saw things and had experiences that have stayed with me for 40 years, so just a little bit worried about fate and superstitions.
in which case, don't get it. From experience i can tell you that taking baby things back to a shop and having to explain why you don't need them anymore is one of the most unpleasant experiences ever