Wiktionary
n. (context idiomatic English) A fact, situation, or personal characteristic, which may be desirable or undesirable, resulting from the circumstances into which a person was born, and which is therefore entirely beyond his or her control.
Wikipedia
Accident of birth is a phrase pointing out that no one has any control of, or responsibility for, the circumstances of their birth or parentage. With a modern scientific understanding of genetics, one can reasonably call any human being's entire genome an accident of birth. The place of birth of a baby has an effect in immigration law of many nations, so that an "accidental" birth in an airport lounge may entitle a person to a passport in later life.
More broadly, gender, family circumstances, cultural background, access to education, inheritance rights, are all examples of accidents of birth. Individual responsibility, from the age of majority certainly, is supposed to cut across all these matters.
"Accident of Birth" is the first single from Bruce Dickinson's fourth solo album, Accident of Birth, released in 1997 and peaking at number 54 in the UK Singles Chart. Dickinson described the song as "about a family from Hell. Except they're in Hell and one of them has accidentally been born, and they want him back and he doesn't want to go. For all the same reasons that you wouldn't want to go back to your family if they're a pain in the ass, he doesn't want to go back to his family. OK, so they're in Hell, that makes a little difference too."
Usage examples of "accident of birth".
That, as he had in the past, for the sake of Rhomatum and the life and responsibilities that were his by accident of birth, he must bend.
The first cause of trouble had nothing to do with the accident of birth.
It never ceased to amaze him how most nobles considered themselves so much better than the people they ruled, even though that rule was always no more than an accident of birth.
She showed him that with age is discretion, with ugliness security from rivals, and that all true gentility depends, not upon the accident of birth, but upon the character of the individual.