"Extraordinary circumstances" refers to unusual and exceptional situations or events that are beyond what is normally expected or encountered. Full definition
Except in extraordinary circumstances (for example, if the mother herself was vitamin D deficient during the pregnancy). (motherandchildhealth.com)
Through a combination of extraordinary circumstances, the central banking community globally has found itself doing unprecedented things. (rba.gov.au)
But as his thinking on the morality of abortion gradually changed, he began to see the fetus as a very important being whose life ought not to be ended except under extraordinary circumstances. (religion-online.org)