I don’t think any amount of situps you do will have any impact whatsoever at shrinking your fibroids. Just take a look in google images at what fibroids look like and try to imagine being able to flatten those things doing situps.
I’ve been doing a lot of core focused work for some time now, and it does nothing to affect the fibroids. At the very least though you will tighten up around the fibroids so any fat there that contributes to the size of your stomach you can get rid of and your stomach will look smaller and stronger, but the fibroids won’t be shrunken as a result of you doing ab exercises.
I was reading some material in which it was suggested that while exercise can’t help you to get rid of your fibroids, it can help prevent fibroids in the first place; but I’ve always worked out since I was a teenager, sometimes 4 hours per day. Admittedly I went through a period of burn out when I was about 34 or so. I stopped working out every day and would go months at a time not working out; but then I would get back on track and I never went years without working out during that burn out period. Additionally I was never one to indulge in a lot of bad food (half the time I wasn’t even eating). I know there are exceptions to every rule; but the same is true for those of my siblings who have had fibroids. None of us were fat and we were all physically fit.
I think there are a lot of conclusions drawn based on certain assumptions and stereotypes about the people who are considered to be ones more likely to develop fibroids and it leads to the spreading of misinformation; but as far as situps getting rid of fibroids, I think even if you took a hammer to a fibroid and tried to pound it flat you might have a tough time getting it done. You could burst it open, sure, but I don’t know if you can flatten that ugly mass of tissue doing 5000 situps per day every day for 365 days.