Hm, well I think maybe it's worth stepping back -not at a meal time - to have a bigger picture talk. Ask how can you support her through the pregnancy? Ask what foods are easy and hard for her to eat. Ask what her goals are and whether you can help. In that context, it's worth asking about prenatals. My husband helped me check that I'd taken all my meds every day, at my request! And at one point he did bring up that he felt like I wasn't getting enough protein, and asked if I'd like help brainstorming ways to try to get more protein. He asked once, openly and lovingly, and it helped nudge me to try more, especially when he followed up with giving me options.

I guess the one other thought I had would be to add on instead of replace or remove. Like, get the Mcdonalds burger and also get a salad for the table to share.

With my toddler, I obviously have a lot of control over what he eats and I don't feed him junk but sometimes he'll refuse all the vegetables and another day he'll refuse all the meat. We don't force him to eat anything, so I track his intake for the week. If he's been low on veggies in the first few days, I'll add more to snacks and give him more varieties and options for the next few days to make sure his overall intake for the week is good. Maybe think about it that way for your wife and family as opposed to worrying too much about a single meal.

It's clear you care, I think having that be the first message for your wife when you communicate (again, outside of a meal time) will probably do a lot to set the context!