It really depends on the medical center, the specific doctor, the couple and the quality of the embryos.

Some medical centers have a policy of transferring either 1 or 2 embryos only, while others will transfer 5 or more embryos if they feel that the quality of most is low.

In general, it has been found that transferring more than 2 embryos does not yield higher pregnancy rates (medical research published in all of the respected journals), so most medical centers are moving toward this direction, in order to avoid pregnancies with multiple embryos and the complications that go along with them.

Newer fertility treatments focus on the use of natural IVF cycles, with the retrieval of a single ovum, its fertilization in a lab & then its transfer, thus avoiding any risk of OHSS (ovarian hyperstimulation syndrome) and significantly reducing the incidence of multiples. 

Good luck!
Rachel Inbar
www.fertilitystories.com