At Federation in 1901, abortion remained governed by the British Offences Against the Person Act of 1861. The Act made abortion illegal under any circumstances. Since then, however, abortion law has remained subject to case law and legislation in each of the states.
Generally, judicial interpretations changed in the late 1960s and early 1970s such that abortions were not subject to criminal prosecution if necessary to preserve the mother's health. Over time this has come to be broadly defined so as to include the mental health of the patient, to which an unwanted pregnancy is interpreted as clinically injurious.