LORELAI: You wanted to control me.
EMILY: You were still a child.
LORELAI: I stopped being a child the minute the strip turned pink, okay?
Lorelai implies that she discovered she was pregnant using a home pregnancy testing kit, the kind where the woman urinates on a stick and waits for the test to change colour, a strip which turns pink indicates a positive test. In fact, these sort of lateral flow tests didn’t become available until 1988, and weren’t widely available until the 1990s, while Lorelai got pregnant in 1984. Previous to this, home pregnancy testing kits were more like mini chemistry labs, where you mixed urine and the solution together to see if it changed colour.
Lorelai claims that she stopped being a child the minute she became pregnant. Getting pregnant doesn’t turn a girl into an adult, so Lorelai is wrong on that count. In fact, we can see during the show that becoming a mother at an early age stunted Lorelai’s emotional development so that her maturity remained at the level of a wayward teenage girl even into her thirties. This is the other side of the conflict between Emily and Lorelai, with neither of them being completely in the right or completely wrong, and with both of them over-dramatising their situations and claiming victim status.
By the way, Lorelai was very far from being rare as a teenage mother in Hartford. By the early 1990s, one quarter of all births in the city were to a teen mother. She was definitely an unusual teenage mother though.