The 200 Pregnant Mexican Women were one of the stages in Cartman's plan to get rid of the PC Principal and the PC Bros. Fraternity.
The plan seemed to consist of using pregnant Mexican women to eat the tacos launched by the taco launchers, then fall asleep and give birth to anchor babies. The PC bros would then be further distracted by a flood of Syrian Refugee Children. (this strategy was meant to mock US Presidential candidate Donald Trumps remarks about illegal immigration reform, which some critics view as racist and alarmist.)