What undergarments are required under my communion dress I am 17 years old?

The Church requires that those who visit a church should present a modest and becoming appearance, without, however, stipulating specific articles of clothing that must be worn. A modest appearance for women would include clothing that some might consider on the somewhat conservative side - looser-fitting, and providing more coverage, than what many would feel is trendy.

my parish is strict and stresses purity and innocence amongst the kids.the girls are required to wear a cloth diaper,plastic pants and tights under their dresses,this applies for all girls up to age 18.i have seen teen girls in the classes as old as 17 and they had the required diaper and plastic pants and tights on under their dresses.you should wear them also to enhance your purity of your first communion.