The competitive "I worked right up until labour and took a Zoom call during the epidural which was performed trackside, get over yourself"...
Some odd attitudes, I very much hope some of the posters here are not responsible for leading teams.
OP, if you don't feel comfortable with it, I would first ask if the meeting can be virtual and explain that your PGP makes long periods of sitting, long walks to platforms etc, very painful. If they refuse,
I would seek a doctor's note requiring working from home / bed rest or sick leave and start mat leave.
FWIW, I did a heavily pregnant train trip for a meeting, became very unwell on the journey, vomited all over myself and nearly passed out hours from home. I turned around at my destination and went home again, declining long distance travel from there on.
It was scary, upsetting and unfortunately no one helped me. In fact, one woman had a go at me as I stumbled, sobbing and faint, out of the loo for taking too long (possibly one of the superior PPs on this thread who would have made a full recovery in half the time) 
If your gut says not to do it, follow that instinct.