5. Child is sick or weak:[1]

One is not to circumcise a sick[2] child until the child recovers and is [strong and] healthy [as prior to this time it is not considered the child has reached the time for circumcision even if it is the eighth day[3]]. This applies, even if the child is only sick in a single limb. Likewise, this applies even if the child is only slightly ill or weak[4] or has a slight pain, such as if he has pain in his eyes.[5] In all these cases, one is to delay the circumcision until the child fully recovers and then is to circumcise him immediately. [Even if it is a case of mere doubt, or a double doubt, one is to be stringent and not perform the circumcision until the child is strong enough and one is not to be lenient in this matter.[6] One must be very careful in these matters, as it is always possible for one to circumcise the child at a later date but it is not possible to resurrect a child.[7] This is in addition to the idea that when one does eventually do the circumcision, it counts retroactively.[8] Accordingly, part of the job description of the Mohel is to verify that the child does not have any medical issues and likewise it is obligatory of the parents to inform the Mohel of any medical issues a child may have had during birth or after birth.[9]]

Waiting seven days from after recovery:[10] If the child became sick in his entire body [such as a fever[11]], or is suffering from acute pain [i.e. acute eye pain[12]], then one is required to wait 7 full 24 hour days from the moment that the child recovers prior to circumcising him.[This applies even if the child was sick for only a short amount of time and then quickly recovered.[13] Certainly this applies if the child needed to be resuscitated immediately after birth that one must wait 724 hour days from after the resuscitation.[14] It, however, does not apply if the child was merely weak and not sick and is now strong enough to be circumcised.[15]] If, however, the child only had mild localized pain, then it is not necessary to wait seven days after recovery.

Delaying the circumcision unnecessarily after recovery:[16] It is forbidden for one to delay the circumcision for even one day past the date the child is deemed medically and Halachically strong enough for it to take place. For every day that a father leaves his son uncircumcised past the eighth day, he transgresses a positive command. [By twin boys, one is not to delay the circumcision until both boys are healthy enough to be circumcised and rather each boy should be circumcised when they are independently ready and strong enough.[17]]

Delaying due to surgery or other medical procedure:[18] It is permitted for one to delay circumcision in order to perform surgery or a medical procedure which is necessary for the child’s health and physique, such as procedures that are done to fix birth defects. This especially applies if the procedure will be taking place prior to the eighth day.

A premature baby:[19] Based on standard medical advice, it is suggested to always wait until the 36-37th week prior to circumcising, even if the child is Halachically allowed to be circumcised.

[1] Michaber Y.D. 262:2; Shevach Habris 9:1-6; See Pesakim Uteshuvos 262:9-13; See Encyclopedia Talmudit Vol. 46 Erech Mila p. 427-431

[2] Definition of illness and a summary of various types of conditions and illnesses that may require deferring the circumcision: See Pesakim Uteshuvos 262:10 regarding fever, antibiotic treatment for infection, respiratory complications and intubation or respirator after birth, lack of blood, blood transfusion, footer hand injury, fractured limbs, a child who fell from a certain height, born with a cleft lip or cleft cheek, child vomiting, child refuses to nurse, premature birth, low weight, cardiovascular conditions or complications, born with a defect or illness

Trusting a doctor’s opinion: See Pesakim Uteshuvos 262:13

[3] See Shevach Habris footnote 7; See a debate in Poskim in Pesakim Uteshuvos 262:9 footnote 63 regarding Bedieved if it is considered that one fulfilled the obligation if he circumcised the child while he was sick, and if Hatafas Dam Bris is still required, although most authorities agree that one does fulfill his obligation Bedieved.

[4] Definition of weakness: See Shach 262:3; Pesakim Uteshuvos 262:11 regarding 1) Looks weak 2) loss of blood 3) Umbilical cord did not fall off.

Regarding low weight: See Pesakim Uteshuvos 262:11 footnotes 92-93

[5] The reason: We delay the circumcision even on behalf of a mere pain or illness in order to avoid any chance of danger. [Shach 262:3]

Eye Pain and eye conditions: See Pesakim Uteshuvos 262:12

[6] Directive of Tzemach Tzedek, brought in Igros Kodesh of Rayatz 9:90, and Igros Kodesh 7:143; Shevach Habris 9:4

[7] Michaber 263:1; Rambam Mila 1:18

[8] Tzafnas Paneiach on Rambam 1, brought in Igros Kodesh 7:143

[9] Poskim in Pesakim Uteshuvos 262:9 footnotes 61-62

[10] Michaber and Rama Y.D. 262:2; Shevach Habris 9:2; See Pesakim Uteshuvos 262:9 footnotes 57-60 regarding dispute if illness must be lethal

[11] Aruch Hashulchan 262:11

[12] Rama ibid; Avoda Zara 28b and Rashi ibid; See Koveitz Or Yisrael 21:11-12 for a letter of the Rebbe Maharash written on the subject

[13] Poskim in Pesakim Uteshuvos 262:9 footnotes 59

[14] Poskim in Pesakim Uteshuvos 262:9 footnotes 60

[15] See Pesakim Uteshuvos 262:11 footnotes 90-91

[16] See Admur 249:6 “and so too the circumcision, even if it is not on the eighth day from birth, it is not possible to push it off to another day, as it is forbidden for one to be left uncircumcised even single day” [See also Admur 248 KU”A 1; Admur 331:4]; M”A 249:5; 568:10; Rama Y.D. 261:1; Rambam Mila 1:2; Noda Beyehuda Tinyana Y.D. 166; Chochmas Adam 149:2; Igros Kodesh 24:396; 7:143; Shevach Habris 7:4; Pesakim Uteshuvos 262:4 and Poskim in Footnotes 23-26

[17] Igros Kodesh 7:143; Kisvei Rav Hankin 2:85

[18] Avnei Nezer  Y.D. 321; See Poskim in Pesakim Uteshuvos 262:2 footnote 5-7

[19] Otzer Habris 8:27; Piskeiy Teshuvos 331:4; Pesakim Uteshuvos 262:10; See Kaf Hachaim 331:2; Minchas Yitzcha 4:123; Pesakim Uteshuvos 262:10 footnotes 79-82; See Igros Moshe Yoreh Deah 2:121 that if a child is in an incubator, he is considered ill and cannot be circumcised until 7 days have passed after he is removed.