Yes a gynocologist would give his/her advice when a patient asks about a certain event. I've read on a site a lady who did show jumping up to 7 months pregnant .. She stopped because it became uncomfortable ..and plenty of others said they continued to do so (baby centre website)
Doesn't mean it's advisable, and do you have a link to this website?
What if their horses had bolted? It can and does happen, so why tempt fate?