I don't have any food allergies nor does my husband. However, I have a sibling that has shellfish allergies. I do have pretty bad outdoor and cat allergies.
I stayed away from shellfish while pregnant but not for that reason. But I didn't stay away from nuts, although there are only a few types of nuts that I really like anyway and I don't really eat a lot of nuts.
I have fraternal twins so both were exposed to the same food that I ate while pregnant (and breastfeeding). One does not have food allergies and the other is allergic to shellfish, peanuts, and a few tree nuts. The one that is allergic also had really bad eczema as an infant.
So, in my experience, it didn't matter. I didn't eat shellfish and one is allergic to it anyway. I ate nuts and one is allergic and the other isn't. I couldn't tell you if eating nuts made the allergic one show symptoms sooner or not. But I definitely believe he had to have some genetic component that predisposed him to be allergic in the first place. Otherwise, eating nuts would have caused the other one to be allergic too. (Standard disclaimer applies....your mileage may vary....I am not a doctor.)
If you are concerned, you should ask your doctor. Or do what makes you feel the most comfortable.
Keep in mind that completely avoiding certain foods, like nuts, can take some effort due to possible cross contamination. There are many foods that are manufactured in a facility that processes nuts, for example, and may contain nuts. I've seen a bag of dried blueberries say that it may contain nuts. I've even seen a bag of fresh spinach say that it may contain shellfish.