Lady Macbeth's reference to motherhood and infanticide near the end of act one of Macbeth remains one of the more enigmatic moments in all of Shakespeare's drama. Fearing Macbeth's wavering commitment to their succession scheme, Lady Macbeth declares that she would have murdered her infant to realize an otherwise unachievable goal. Scholars have traditionally read this declaration as evidence of Lady Macbeth's attempt to seize a masculine power to further her husband's political goals. While she clearly seeks power, such power is, I would argue, conditioned on the maternal, an ambiguous, often conflicted status in early modern England: one which enables Lady Macbeth to slip the gendered constraints that bind her. This paper examines representations of murdering mothers in Elizabethan and Jacobean assize records alongside Shakespeare's Lady Macbeth, arguing that the maternal ultimately represented a threat to the process of patrilineal transmission in early modern England.