: to everything Gena said.
I also found out at 20 weeks and I made it a goal to gain at least 40 pounds for my pregnancy. I managed to do just that! I did make every bite count and really focused on both protein and water. I also took it VERY easy from about 28 weeks on (stopped the kids extracurricular activities, let the house go, didn't do a lot of running around) and from 33-36 weeks I went on a very modified bed rest. I had someone at my house every day taking care of my older four and making meals. I slept a lot and rested on the couch. I really contribute that with carrying them to 39 weeks. I had a few runs of scary, really intense contractions around 32-33 weeks and my midwife strongly recommended that I take it WAAAAY easier than I was. Afterward, while I still had contractions daily they were much less intense and definitely more braxton hicks.
Expect to be hungier, more thirsty, more tired, and needing more rest. Expect that the pelvic pressure at the end will be intense. Expect that you will possibly have a pubic separation. Expect that you will probably be crankier and more moody than regular end of pregnancy. Expect to have more fears concerning the birth and make a good attempt at working through those so they don't hinder you. Expect to have to stay open to mode of birth--sometimes they chose a different method than you'd like.
I had my babies at home but some women choose to have their twins in hospital even if they've had a previous home birth. There is no 'right' answer. I also had an unhindered breech birth.
The journey to my twins was very simply amazing and transformative.