> What is the reason for this?
"...[I]f the child is not born by natural childbirth, but is delivered
instead via Caesarean section, then the child's brit (circumcision) will
not take place on Shabbat. Instead it will be held on the following Sunday.
The reason for this is that the biblical requirement for actually
permitting the circumcision on the Shabbat is predicated on natural
childbirth, so that Shabbat is truly the child's eighth day.(p. 8)" He
gives as a reference Shulchan Aruch, Yoreh Deah 266:10