House suspects she may be pregnant, but Margo displays sudden irritability, which confirms Foreman's suspicion of Huntington's disease.
Cameron and Foreman find Margo's daughter's Ritalin in the car while searching her house for drugs.
Margo's initial tests for cancer come back negative, but House persists and orders a biopsy to find the suspected tumor.
House is not convinced that the symptoms indicate a liver tumor and suspects that Margo was secretly using birth control pills to negate the fertility treatments.
The combination of Ritalin, birth control, and fertility treatments caused the tumor, which House believes should be benign.