Wedding photographer and pregnant

I’ve being asked to do a wedding I’m a photographer but when the wedding is I’ll be 31 weeks pregnant! I really would need the money but it would be an all day job and I’d have to be on my feet for atleast 13 hours! And running around anyone who is a photographer knows this Should I tell them I can’t do it or try and explain how I’d need to sit down or take rest? I don’t know what to do 😭