My case is a little different as I didn't know I was carrying twins until 39.5 wks! I think that made all the difference. It was my first pregnancy & I didn't realize I was going through anything different than any other woman. Other than some seriously low iron at the beginning of my 2nd trimester, I felt great until around 36 wks. I work in a health food store & am on my feet all day. The last month was very painful on my back & hips. I also had a ton of intense BH contrxs.
It's all ab/your diet. Lots of protein & lots of minerals! Take a really good prenatal like New Chapter & consider everything that goes into your mouth. I lived off of eggs, kale, apples, & almond butter. I ate some sweets (more than my share that last month) but only after I had met my requirements. I made a chart of all the things I should eat in a day & checked them off. I followed the Brewer's diet pretty much, but I don't do dairy except kefir & yogurt, so I got calcium from other sources.
Red Raspberry tea is the best thing you can do. Yes, it will cause a lot of BH's, but it will really tone your uterus which you need. It is being seriously overstretched & you need it to contract effectively after the birth. Twin placentas are double sized (duh) so heavy bleeding is more common postpartum. Nettle tea is also important. Lots of vitamin K to prevent the heavy bleeding, plus tons of easily absorbable vitamins & minerals. It is also a mild kidney tonic helpful in late preg, esp w/twins. Both of these herbs can be thought of as food & drank as teas in abundance.
I worked right up until the day I found out I was having twins at 39.5 wks & delivered at home 2 days later. 7 lbs each. Dr's often stress you out & tell you to expect to deliver early (they consider 36wks term, I think that's crazy) but you can carry those babies all the way. Take immaculate care of yourself, and most importantly, TRUST that you can do it. Your body can carry those babies.
I am proud of my birth story ( as all mothers are) and I tell it to inspire other moms w/multiple pregs. Also, I am a doula and soon to be apprentice midwife. I want to see more safe twin births!