When I was pregnant, I didn't put on a lot of extra weight. It was one of my (silly) pre-pregnancy notions that I was going to be able to wear my wedding rings my whole pregnancy. But at around 7 months, we went to Hawaii on our post-Bar celebration/babymoon trip, and the warm weather and humidity made my fingers and feet swell up. Had to soak my hand in ice water to get my rings off, and couldn't put them back on until we got home. And even then I couldn't wear them regularly until after my son was finally born.
It doesn't take pregnancy to cause joint swelling. Humidity and temperature change (and aging) can cause our joints to swell. And we've all been in the position of momentary panic when trying on rings in a store where we can't get them immediately off, and you're twisting and grimacing and praying you can get it off.
This is where my mom's wisdom comes in. I had never heard this before, and no one I have shared it with yet has either, but it absolutely works.
Next time you have a ring on your finger you can't get off, spray it with a little Windex. That's the trick. The liquid consistency easily and immediately lines your finger and the ring, and it will slip right off. Non-toxic, and with a quick rinse of both hand and ring when done, you're good to go.
One other key to getting a tight ring off your finger is not to straighten your finger. A straight finger causes the knuckle skin to bunch up at the join and makes it even harder to remove.