The thing that's important to keep in mind is that virtually all the swaying info on all other sites comes from the same 3 theories that were all invented 50 or more years ago. Once these things were tested with new technology then it became apparent that they weren't correct, but the theories were so ingrained that people think they have to do things that way. The only reason why they all seem to agree except for us, is just because they're using the same old things over and over.
It's ok to get pregnant at a lower weight BUT my rule of thumb is BMI of 21 - try to hold steady. If a little more weight sneaks off after that, it's ok. But don't drop below 18.5 no matter what. EVen if it means increasing calories, we've had success up to 2000 cals a day as long as the protein and fat are kept under control.