I don't agree with what's being done here.
At 17 weeks the fetus is not independently viable, i.e. it could not survive on its own outside the mother's womb. Some might argue that the mother is clinically dead - she has no consciousness and that if her life support machine were switched off, she would stop breathing and die. But the same could be true of the fetus too - without the mother's placenta, it would die - why does the right of the fetus trump that of the mother in this case?
How long would the mother need to be kept on life support for? Until the bare minimum 24 weeks or longer to ensure the best possible outcome for the fetus? That would mean keeping the mother on life support for at least another 7 weeks, not without further risks such as blood clots and infection. The risk of these occurring would become higher as the number of weeks on ITU increases and at 24 weeks there would be a high likelihood of very poor outcomes for the fetus, even in a healthy pregnancy.
I can't imagine how distressing that would be to the woman's parents who have expressed a wish for her to be allowed to die. Intensive care units are not nice places, sterile, bright, loud, constant monitoring with machines, injections, lines, catheters; all of this knowing that their daughter is ultimately going to die after undergoing a caesarean section, presumably after which her life support machine would be switched off - after all there would be no reason for her to go back to intensive care.
In equity terms, ICU beds cost at least £1000 per day per patient, probably more depending on the condition. Is it fair and right that a patient who is brain stem dead and has no chance of recovery is kept alive at the expense of others who need the funding and indeed even the physical bed in order to stay alive? It might seem callous but it is a real consideration I think.
I think if the pregnancy was further along and there was a possibility of delivering it i.e. 24 weeks or more, it would be a very different ethical situation to consider, but for me it just seems wrong to not allow this woman to die.