You must show valid travel documents as part of the entry procedure into the United States. The documents required depending on the country from where you are arriving and your citizenship or status.
From Canada, Mexico, and Bermuda
The Western Hemisphere Travel Initiative covers travel by land, sea or air from Canada, Mexico, and Bermuda:
American citizens entering the U.S. must show a valid passport, U.S. passport card, Trusted Traveler Program card (NEXUS, SENTRI, Global Entry or FAST), or an enhanced driver’s license.
Permanent residents and foreign nationals living in the U.S. should have their passport and they may need to show. If applicable, their U.S. visa and/or alternate or additional travel documents also may be needed to show.
From Other Countries
All travelers entering the United States from all other countries need a passport upon arrival (regardless of their country of citizenship).
Permanent residents and foreign nationals may also need a U.S. visa.
Entry Denials
Customs and Border Protection (CBP) officers will conduct arrival inspections using the same criteria for all foreign nationals visiting the U.S. They have the ole discretion concerning your admission to the United States, even if all your travel documents, including your visa, are in order.
Note: There are no rules prohibiting pregnant visitors from entering the United States, doing so to give birth is not one of them. A CBP officer will consider your pregnancy when deciding on your admission.
For more information on entry visas, please visit United States Immigration Department
By Premji