Marge uses this home pregnancy test on the episode "I Married Marge" after she began to suspect that she may have been pregnant with her and Homer's fourth child--Homer bought it because it came with a free corn cob pipe. The directions stated: Ahoy maties, if the water turns blue, a baby for you. If purple ye see, no baby thar be.
Marge's test turned out pink instead of blue or purple. Checking the box again, the directions stated: If ye test should fail , to a doctor set sail.
As a result, Marge went to go see Julius Hibbert, their family doctor--at the end of the episode, Marge revealed to the family that she wasn't actually (which she and Homer were ecstatic about).