This is the article about surgery on a fetus in the womb at CBC news.
"A baby's heart was repaired while she was still in the womb, which doctors at Toronto's Mount Sinai Hospital and the Hospital for Sick Children called a first in Canada."
What does the blue mean? Doctors called on a telephone first in Canada? Doctors succeeded in that kind of surgery first in Canada? Isn't "the first", not a first, correct? I learned that I should put "the" in front of first.
There are many things that happen for the first time, many that happen for the first time in the field of medicine, and many thing that can happen for the first time in Canada (even if they happen somewhere else before then).
This was the first time this type of surgery was done in Canada, so it was "a" first. (The next day, another new surgery could have been done for the first time, making that another first.)
They referred to it as "a" first, because there are many other types of first that can exist.