1,117. A Baby Who is Sick

163:4 We must not circumcise a baby who might be sick because safeguarding life takes precedence. This is because a bris can always be performed later but it's impossible to restore a lost life. See Yoreh Deah 262-263 regarding when to circumcise a baby who was sick and recovered. As soon as the baby is fit to be circumcised, it is forbidden to delay the mitzvah any further for any reason, such as to have more time to prepare; the baby must be circumcised as soon as he is fit, though not on Shabbos or yom tov.

163:5 If a woman lost two sons because of circumcision and it seems that the circumcision weakened them, the third son is not circumcised until he grows up and becomes stronger. Similarly, if a woman lost one son because of circumcision and her sister had the same thing happen, then the rest of the sisters don't circumcise their sons until they have grown more and become stronger.