Talk to your doctor. You might also want to ask a pregnancy subreddit (r/babybumps). AFAIK, you shouldn’t drastically change your diet just because you get pregnant, except to stop restricting and make sure you get the nutrients you need. OTOH, fasting isn’t recommended for pregnancy. IF feels very natural to me. When I’m pregnant, I plan on loosely continuing IF but letting myself eat outside my window whenever I’m hungry.
Just to reiterate, this is a situation where you should just talk to your doctor and not take advice from Reddit (besides my advice to talk to your doctor ;)
I have a similar concern because I have a 2.5 year old and we want to have another one. My doctor had said last time that I shouldn’t gain more than 15-20 lbs because of my BMI. However, I ended up gaining a lot more due to swelling and water weight. This time I asked my doctor how I can avoid gaining excessive weight. She said that a common misconception people have is that if you’re pregnant you have to eat more. Actually you have to eat the same amount but you should make sure to eat healthy, whole food, avoid excessive sugar, etc. The water weight and swelling is out of your control though
Edit: and of course exercise is important!
Nothing - absolutely nothing - is as important as providing all the nutrients the developing fetus needs. Weight gain is frequently a consequence of pregnancy- but you can loose it AFTER the child is not dependent upon you for everything nourishing.
Fasting during pregnancy is tantamount to child abuse. It’s selfish.
Once you’re a mother (or father) your child is your first and only priority.