If a women get pregnant in the United States

Huh ?

Usually citizenship rights and obligations are based on location of birth rather than location of conception, which may be difficult to determine. It would be important to have some more facts however about whether the child has been born and if so where, and what your specific concerns are with regards to United States jurisdiction.

Your belief is not accurate. Many countries around the world have treaties that permit the law to cross borders with the people. You need to consult with a family law attorney familiar with immigration. I am aware of international cases and enforcement of domestic relations cases across international borders.
I do not see how this question falls into the "Brain Injury" category?

Someone has to be living in the United States to file an action for paternity. The action would then be filed in the county of the state either party is residing. If the other party is in a foreign country, enforcement and establishing paternity and support would depend upon whether that country participating in any treaties with the United States concerning the establishment of paternity and support.