I had 4 Weddings, some hens nights, & so on in my 2nd & 3rd Trimester. I just think about the event itself, will you be able to sit down & so on, ex hens night on a bus, home late....not for me. With the Weddings as they were close to my due date etc I just went to the ceremony & not the receptions. One Wedding I went to both Ceremony & Reception & stuck it out til 12....thought that was a good effort. If it's something that you can get away without an RSVP & just rock up if you feel like it then I would do that also. Though as someone said, you don't always feel as tired. I actually never really slowed down myself.