Family Guy Episodes :- Emission Impossible

Lois and Peter plan to have another baby. Stewie fears that they will ignore him if they do this. He wants to stop them from going in for a new baby, so he makes sure that they never sleep together. Finally, Stewie downsizes himself and gets inside Peter’s body with the intention of ridding Peter of all his sperms so that Lois may not be able to conceive.