Conversation so far:
what episode of er does carol have her babies
Great Expectations is the eighth episode of the sixth season of ER. It has Carol Hathaway going into labor complications while on an El train on Thanksgiving.
when did the er episode great expectations air
The ER episode Great Expectations first aired on NBC on November 25, 1999.
what character was introduced in the er episode great expectations
The ER episode Great Expectations is also the first appearance of Maura Tierney as O.B. nurse Abby Lockhart as she helps Carol on her delivery.

Question: when did the character become a series regular
Self-contained rewrite: when did abby lockhart become a series regular in er