Health: as I mentioned previously, HaRav Elyashiv considers more than three fetuses to be potentially life threatening to the mother. This is a liberal definition of sakana, and he only uses it to allow “reduction” until 40 days.
I have heard of an incident where an expectant mother was diagnosed with cancer, where the chemo would inevitably provelethall to the fetus. Since thebabyy was in no form a rodef, she received a psak that she could not treat the tumor until after the baby’s delivery, which was carried out at the earliest possible date. It was known from the outset that this ruling would seriouslyendangerr the mother’s life, and if fact she survived only a few weeks after delivery.
This seconincidentnt is NOT something I would even consider Paskening myself. Life and death rulings should breferreded to Gedolei HaPoskim