It is wrong to ask you to never speak to your mother again. No one should ask you to choose between your family and them (even your wife!) That's very poor and even abusive bahavior.

Next, your wife is behaving very immaturely. She can't get pregnant to instead she is acting jealously over your mother who did get pregnant. If it is such a huge concern to her, then she should bring this issue to her doctor. There is a saying "better to light a candle than to curse the darkness."