Hi there - this worked for me.
My last (as in no more, not ever again, I don't want a fourth child....no no noooooo) pregnancy I hadn't discovered the joys of knicks. I started riding a few months before becoming pregnant. Initially I was too knackered to ride but by about 10 weeks was back into it.
I used a pair of cotton bike shorts (from target) that was 2 sizes too big. I had a gel cover on top of the gel girly saddle. Inside my undies I had a panty liner which helped marginally. The smaller of the TENA LADY range was best. I showed early on with all my pregnancies and got big enough for ill mannered gits to ask if I had more than one inside. The cotton bike shorts just stretched with me.
I rode the bike up to about 32 weeks but only two days a week for short distances - up to 10kms. I also walked our dogs on the other days of the week, about 3 kms. By 32 weeks I found that I was knocking my tummy with my thighs as I pedalled, made me extra special breathless. Also had lower back problems and abdomnal muscle problems. Specialist physio cancelled all exercise, prescribed weekly physio sessions and a special elastic girdle.
I think the exercise helped my recovery in the weeks immediately after delivery. Took a long time to get back on the bike, mostly because of bugger all time with 3 young kids.
All the best