No sex?

We went to the doctor for our first appointment at 10 weeks (we were previously at an RE because we conceived via <a href="">IVF</a>). We are having twins and everything looked great on the ultrasound. When we had our consultation with the doctor he told us we had to be extra careful because we are having twins and said that we should not be having sex (penetration) for the entire pregnancy! I trust him and know that there are other things we can do for the next 7 months but was curious if anyone else was given this advice from their doctor?