This episode aired in February 1993. Janet Hubert, who plays Vivian Banks, was actually pregnant at the time and also had her son in February 1993.
When Vivian's sisters begin to arrive, Will makes a joke to "Never feed her after midnight." This is one of the rules from the film "Gremlins" on how to care for a mogwai. If a mogwai eats after midnight, it turns into a gremlin.