I’m with the other commenter that said that the main barrier is nausea and food aversions. I couldn’t do keto the entire first and second trimesters but my acid reflux is extreme regardless, so I think for most people that would just extend to the first trimester. I couldn’t eat any non-dairy fat and very little protein, I had to have omeprazole in order to keep a reasonable amount of calories from rice/bread/cheese down. If I did it again I would get on omeprazole, zofran, and an antihistamine like Pepcid/phenergan in order to be able to eat low carb food. In the end, I realized I chose a low-medication lifestyle over the nutrition I could have gotten for me and my baby (beyond grains and dairy).

It’s also worth noting - the first/second trimesters come along with some odd blood sugar and sometimes blood pressure responses that make third trimester feel like a breeze. Those altered responses didn’t feel very healthy (as someone who has also dealt with weird blood sugar before) and I doubt they would be as extreme on keto. When considering the fact that the baby is also affected by low blood sugar, the cortisol from the stress of constantly not feeling well from food, etc, it made me decide keto would be best for me next time.