Baby Aspirin and the Pill
A woman came home early from her night job to find her teenage daughter on the couch with her boyfriend, right in the middle of "the act." The mother threw the boy out and gave her daughter a good talking to about the dangers of unprotected sex and accidental pregnancy. But the girl reassures her mother that she doesn't have to worry. The girl has been taking her mother's birth control pills.
The mother is confused by this because she hasn't noticed any pills missing. Well, the daughter says that she's been replacing the pills with baby aspirin.
A few weeks later, the mother discovers that she's pregnant again. This confuses her because her husband has been away on a building job for two months. That's how they discovered that baby aspirin can make you pregnant.
Behind the Legend
The baby looked just like her mother since they had identical genes and grew up to be Melissa Gilbert, the star of television's Little House on the Prairie.