Cat and My Belly

I'm 16+2 and I have a fixed male cat who weighs around 20-25lbs. He's a Maine coon and huge. He's 15 years old and he's always been my lap cat. I know the baby is very well protected from bumps and tumbles of the belly but is it safe more my cat to lay on my belly and step on it? Cats are somewhat hard to "train" or correct and being he's old and already set in his ways, it would be even harder. He isn't aggressive, and he doesn't use his claws when he steps or lays on me. Since I've become pregnant, he's a major snuggle bug.

I just fear that his weight may be a possible problem?