It depends on whether they can use their eggs and sperm or not, if we are talking about heterosexual couples who work with a gestational surrogate. As for gay male couples, they can mix their sperms and fertilize the egg without knowing which one of them is the actual biological father, which means that at least will look like one of them.
Read the full article on: Parents through Surrogacy Guide – The Process Step by Step ( 78).