Mother figures are an extremely common trope in literature. They are asexual, kind, warm, nurturing women who act as caregivers for other characters. Lady Macbeth is an oppositional figure to this device. She is ambitious, cruel, and sexual. She greets her husband passionately, and displays clear power. In the play, there is a vague reference to a child she and Macbeth had conceived together, who might possibly have died. This, combined with her famous line about her willingness to dash the brains out of an infant, presents her as a woman with a metaphorically cold and barren womb.