Congratulations, first of all!!
There is differing opinions on weight gain with twins. I was worried especially in my first trimester, that I wasn't gaining enough. The book "When you are expecting twins, triplets, and quads" has you worried if you haven't gained 20 lbs by 20 weeks. It insists that you need to gain a lot of weight, and earlier rather than later with an end weight gain of 45-55lbs!
As I am barely 5'1" I was very worried about such an amount of weight, but also worried because I didn't gain a lot early despite eating "well".
My OB was great and very reassuring. As long as the babies are growing well, you will be fine. I would definitely NOT try to restrict your weight gain however. In fact, I started drinking ENSURE to make sure I was getting enough calories and protein for the babies.
For the record, I ended up gaining 35 lbs (although I gave birth at 33 weeks, so it would have been more if I had continued on) after a slow start.
My advice? Eat well--nutritionally. Gentle exercise if you can. Take care of yourself. Don't overdo it. Think positively!
PS. I have lost ALL my weight already at just 4 weeks! Breastfeeding twins is a serious calorie burner.
Me: 44, endo. & 1 tube due to rupture
DH 36 fine
IVF#1 double ectopic/severe OHSS 12/08
IUI#1, #2, and #3, 2010 BFN
IVF#4-2/11 HPT=BFP 11dpo; 13dpo=240! 15dpo=653, 20dpo=5522,3/29=u/s-1sac1yolk 4/4=2 HBs!