I am fully aware of the progression of a spontaneous abortion (stage 1 threatened, stage 2 inevitable, stage 3 incomplete, stage 4 complete). However, there is still a risk the patient could delivery a live-born fetus (liveborn by definition is taking a breath, having a heartbeat, noting a pulsating cord at the time of delivery, or having muscle movement -- regardless of the length of time this continues after birth. If the infant takes one breath, the coding scenario changes to an early delivery and not an abortive outcome per coding clinic guidelines.
If the physician's office codes an abortion then the facility codes a live birth, an audit could begin from the insurance company. Granted, the risk fo this occurring is remote, but that is the reason I would code hemorrhage of pregnancy up until the time the spontaneous abortion actually occurs.