Of course a woman could throw caution to the wind. It's possible.
I think equating Madeline's visit to a royal tour is a stretch. But I'll give you Maxima. She visited Japan during her second pregnancy, correct? I don't really follow the Dutch so my memory on them is hazy.
With the Cambridges going on tour in December, I would be very surprised if they did a second foreign royal tour a month later. Especially, since William is starting a new job and he isn't the heir apparent like W-A was. But they have surprised me before!
I mentioned it above, Max visits Kenya, Uganda, and Japan while pregnant with Alexia, and she visited Australia, New Zealand, and Turkey while pregnant with Ariane.
And I wasn't comparing Madeleine's trips between the US & Sweden with a royal trip, but just the flying back and forth in her last trimester. Nothing Madeleine has done, ever, could be compared with the day-to-day of a royal trip.
Max had a difficult pregnancy with Amalia, which is why she wasn't seen often. However, it seems she had a far better time with both Alexia and Ariane since not only was she busy in the Netherlands, but she traveled outside on several occasions.
I don't think any royal family rules anything out until the end, re: trips to be made, particularly when pregnancies are involved. I am sure, if Kate is up to it, she may go, but that's for Kate and her doctor to decide.