During green card processing by USCIS, the concern is with the birth certificate of the foreign national. For example, many applicants from India do not have a valid birth certificate. Instead, they have a hospital record of the fact of the birth but without the names of the parents. This situation would then require secondary evidence as proof of the birth. However, as the U.S. citizen petitioner, you also must document your U.S. citizenship and there are several options as to which document to submit to USCIS to prove your US citizenship besides the U.S. birth certificate. A favorite is the biographic page of your U.S. passport. Take note, however, that the passport must be unexpired. If you need a new passport in a hurry there are 24 hour services that can oblige. Instead of the passport you can also show a copy of your Certificate of Naturalization or Certificate of Citizenship, or a copy of Department of State Form FS-240, which is the Report of Birth Abroad of a U.S. citizen. Remember that as the U.S. citizen you will need to submit two copies of proof of citizenship – one for the petition itself, or Form I-130, and one for the Affidavit of Support or Form I-864.