OP first doublecheck if it is flea dirt or just bits of dried mud.
It’s really easy to tell if it’s flea dirt, (@dementedpixie ) It’s usually obvious from the shape, as flea poo has a curving shape, and also if you dab it with wet cotton wool then flea dirt turns reddish/brown as the dried blood dissolves. Other dirt just stays its original colour.
OP your biggest health problem re the pregnancy isn’t so much the fleas, as the chemicals you’ll need to use to treat the fleas. Don’t rush to the pet shop and buy all the flea bombs etc, instead speak to your vet about what to do but basically you’ll need to treat the cats (Advocat or Frontline drops are usually best, depending on your area as some areas have immune fleas) and also spray your house with flea killer. For Advocat you need a vet prescription.
No point spraying eg a tiled floor you want to do carpets, under sofa cushions, cracks between floorboards etc. But be aware that this spray is a poison and treat it like one. You as the pregnant mum need to not handle those chemicals get your partner or a pest control guy to do it. And ideally someone should air the place out for a few hours before you return.
It will take about 3 months to get rid of them as nothing kills flea eggs so you’re killing them when they hatch which can take a while. Vacuum lots and get rid of the vacuum bag often otherwise they can hop back out of the vacuum cleaner.
Good luck. It happens a lot we just don’t discuss it much.