Hi there!
I had the same issue and after a lot of random searching on the internet, I found the resources quite thin on the ground. It seems to differ from woman to woman and also depends on the type of IBS you have.
I used to have flare ups during my period and I found that the early symptoms of pregnancy ibs to be similar.
Long story short, I ended up visiting occupational health with work and the Dr I saw stated that the two (ibs flare up and early pregnancy) was unlikely to but related at this stage in the pregnancy due to the size of the baby. I was 9 weeks when I went. He also said that as the baby grows ibs will get worse due to the pressure on the bowel.
From my perspective, this totally negated my experience of early pregnancy ibs, he seemed happy to blame it on my eating habits. Of course, he is the medical professional but as I said I do think early hormones factor into some what. Particularly as you said, you had it under control previously.
Mine did get better as the first trimester went on but was replaced with some heavy duty constipation. I would attribute that to the pregnicare vitamins I was taking but to be frank, it was something of a relief after several weeks of the other type of flare ups.
Getting towards the end of the second trimester now and it's started back up as the GP suggested it would. It seems to be triggered by the baby's movements but is more predictable and therefore more manageable then it was in the early weeks. My ways of managing it have been the following : peppermint tea (I use the Harrogate brand they are expensive but they work for me as they are not as weak as other brands) , continuing to take to vitamins and treating the constipation with diet, and avoiding fried foods. This seems to be working okay.
I'm not sure if that method will work for you, as you said you will managing it before. It may be that you to have to step up your own routines or bear with it until it passes if you're not in too much pain.
There is the option of going to your GP but there's not much they can do unless you want to take prescription anti-spasmodics. If that's what you want, maybe book an appointment to discuss with them. They might be able to give you information on diet but I'm sure you know that already.
I really hope this helps, it can be hard to find information but this is what I found with my ibs and pregnancy.
Best of luck with everything and congratulations on the pregnancy. Hope you feel better soon.