I haven't had contractions yet, but I have had round ligament pain. When it's round ligament pain it happens more so when you getting up from a sitting or laying position and your muscles are stretching. It doesn't occur at regular intervals, but happens more so with any movement.

Contractions feel like strong menstrual pains. RL pain is more when you make a sudden movement.

Contractions will usually make your belly feel hard and tight. As you get bigger, they might take your breath away as your uterus hardens against your diaphragm. It's normal to have contractions throughout pregnancy (although they usually don't hurt), as long as you're not having them regularly. My doctor's standard is no more than 4 in an hour.

Since you're carrying twins (which I was the last time), your uterus is stretched farther than it would be at 17 weeks with a singleton (obviously!), and you are way more likely to have RL pain more often, and sooner than a singleton mom.

The difference between the two is the feeling. RL pain is PAIN...like someone kind of stabbed you, or pinched you. Contractions are like menstrual cramps. I found that when I got contractions, they made me feel kind of sick...though I should mention that the ONLY time I got contractions that I knew of was the day I went into labour with them...so I'm certainly not an expert! LOL!

Honestly I could have had contractions and not noticed because couldn't notice that my belly got hard--because my belly was always hard as a rock from squeezing two babies in that space. And I did just read in "What To Expect When You're Expecting" something about how it's normal to start having contractions at like 20 weeks, as long as they are irregular and you only have a few every hour. It's "practice" for the big day. (And with twins, that day is probably going to be sooner than most.)

: ) Congratulations on your pregnancy! Twins are just amazing. : )