why is the U.S deparment of State denying me a passport?

I applied for the first time for a passport book more than a month ago, now I received a letter from the U.S department of state telling me that they need more information about my birth, because in the year I was born (1964) the midwife that attended my birth was suspected of illegally register childs, but that's not my case because a doctor delivered me, my parents were permanent residents at the time I was born. Yesterday I returned the letter they sent me with several documents from my parents and also my birth certificate and a letter from the doctor that delivered me, now I'm waiting for their answer, I want to know if this is happening because I applied for a U.S passport book? Would this thing happen if I applied for a passport card instead?