You can get a travel medical insurance for the visitor coming to the US for a short trip. The policy, however, covers only new medical conditions and travel emergencies. Pregnancy, maternity, and pre-natal care is usually not covered under short-term visitors' insurance. You may consider a policy like Atlas America Insurance which may cover for complications of pregnancy, along with any other standard travel insurance benefits for US visitors.
Atlas America Insurancehttp://www.visitorscoverage.com/atlas-america-insurance/
Learn more at: Travel Medical Insurance for Pregnancy
Insurance rates are regulated by law. You can't find the same insurance plan for a lower price anywhere else