Some friends of mine would like their baby to be born in the US, so that their child can obtain US citizenship upon birth. They both have a valid B1/B2 visa and have traveled to the US before. They will pre-arrange a contract with a hospital and buy medical insurance, so they won't rely on free emergency care or otherwise use up American budget funds.
Would it be legal for them to travel to the US explicitly for the purpose of giving birth? If not, what visa should the mother apply for?
There are obviously other issues such as whether or not airlines will agree to transport the mother during late pregnancy, but that's out of the scope of the question.