Congrats!!!!! I also have beautiful twins (b/g) and they are almost 17 months (natural). Just to warn you, it is a bit crazy in the beginning with round the clock feedings for 2 little ones (my husband & I didn't quite know what to expect), but it DOES get easier. As soon as the babies sleep for longer periods at night, life gets better. Every minute with them is absolutely priceless. There was nothing better than cuddling with the 2 little ones at the same time= so sweet- we feel so incredibly blessed!
As for labor, I did go into preterm labor- I had them at 32 weeks. For the last week before they were born, I began feeling much worse- I really slowed down, was sore all over, had carpel tunnel, had a ton of braxton-hicks etc- I told my OB about it & she just kind of shrugged it off & said all of the stats are fine (blood pressure, heart beat, etc) & not to worry or do anything different. That night, I went into labor & my OB didn't come to the hospital until I was in the OR the next morning (had to have a c-section b/c lower twin was head up). So, my advice is to make sure your OB listens to how you are feeling. And to make sure you have an OB you really like. Don't be afraid to speak up.
Needless to say, Albany Med did a great job- the c-section was not a big deal, so don't listen to all of those horror stories. The twins spent 3 weeks in the NICU and are happy, strong & healthy. The nurses & doctors there were incredible- they were in excellent hands. Very professional & caring!- We could not have been happier with the NICU there.
Also, I read afterwards that moms of multiples need tons of rest towards the end of the pregnancy- 2 naps a day, should make sure to minimize stress, & should eat a lot of omega-3 with DHA (helps to prevent pre-term labor). (My OB didnt' tell me any of this). Dr. Barbara Luke's book- When You're Expecting Twins, Triplets, and More was a really useful book- I totally recommend it. Her advice is really great.
Chances are you won't go into PTL too early, so try not to worry about it. There are things that I think you can do like, eat right, get tons of rest, try to stay relaxed, and read that book for extra tips on how to manage the pregnancy. I wish I had read it more while I was pregnant. I'm so happy for you & know what an exciting time this is. Enjoy it! Congratulations! With such great medical care in out area, you'll do great no matter what happens.