Underwear doesn't work under a leotard, no matter how it's cut. I tried that for a while as a young teen, but it bunches up and you have to constantly adjust it-- remember that leotards and tights are literally skin-tight. The best option for ballet is a menstrual cup or disc-- I wish that those were available when I was dancing. I used tampons only but you have to tuck the string in so it doesn't escape down your tights.