564. What Kind of Bris is Not Held on Shabbos?

Milah 1:11

A bris does not override Shabbos if the baby was born without a foreskin; was born not completely formed in the eighth month of pregnancy, as such a child was not expected to survive; was born by C-section; is a hermaphrodite; or was born with two foreskins. Such babies are circumcised on Sunday, the ninth day.

Milah 1:12

If a baby is born during bein hashmashos, which is the period when it is unclear whether it is day or night, we count his birth from the night and circumcise the baby on the ninth day, which could be the eighth day. If a baby is born during bein hashmashos on Friday, his bris does not override Shabbos, because Shabbos prohibitions are not overridden in a case of doubt. In such a case, the baby is circumcised on Sunday.