A genuine question

So I:m not pregnant yet as I decided to lose some weight before we start trying. I have this fear of me getting obese again once I'm pregnant and post partum because losing almost 30kg so far has been very very hard and dont want to go through this again. I've seen that pregnant mommas can go to the gym/workout. I've also seen a lot of moms that had defined abs before getting pregnant and their belly wasnt as big, so now here comes the question - im already working on defining my ab muscles and want to know if the same thing can happen to me (that i dont start showing quick and dont have a big belly). i do think that all pregnancy bodies are amazing but its just this fear in my head that im going to be obese after i have a baby, because this is the hardest thing i ever did in my life