Is there an issue with ladies going to the zoo when they are pregnant? If yes then why is it a problem?
The mekor is based off the Sefer Habris which explains it is not good for a pregnant woman to see strange things and then get scared which is bad for the baby. See here for answer #399 .
I see two mekoros; the sefer habris and the kav hayashar. I have been unsuccessful in finding any mekor in sifrei halacha and minhag (bar ilan didn't offer anything, but i'm not the greatest at searching...). I don't have access to these two great sefarim, but then again i understand that these sefarim say many things that we don't necessarily follow. I heard about this minhag from my mother and mother in law, and I would like to know if this minhag is the product of folklore so to speak, or it is actually endorsed by rabbanim.