MARGO: You bought the new girdles a size smaller. I can feel it.
BIRDIE: Something maybe grew a size bigger.
MARGO: When we get home you're going to get into one of those girdles and act for two and half hours.
BIRDIE: I couldn't get into the girdle in two an' a half hours...
It's not just romance that Margo's insecure about. With age, she has to work harder to maintain her figure. It's not just vanity. It's critical for a woman in her profession to look slim and glamorous.