In ethical terms, the death if Rosie was a completely foreseen, but completely unintended, double effect. If they could have saved both, I am certain they would have done so. An in fact they kept trying to do so, within the limits of the possible.
Several decades ago my wife and I had our first daughter at home. As part of the preparation, we took 80 hours of emergency childbirth training.
One of the instructors had been a midwife waaayy back in the boonies of South America for several years about 30 years earlier. She showed us her medical bag and tools.
One of the tools was very oddly shaped. When I asked about it, she explained that it was used to decapitate one baby of a set of twins when necessary.
I was of course appalled. She explained that twins are not uncommonly oriented so that one is breech and the other normally oriented. Their heads can interlock so that neither can be born.
As a midwife, she wasn’t allowed to do a C-section. There was no way to get a doctor to do one where she was.
If she did nothing, both babies and the mother would all die, after immense suffering.
So the answer was to cut the head off one baby so the mother and the other child could be saved.
Sometimes terrible things are necessary.
While she had been trained in how to use this equipment, she was eternally grateful that she hadn’t had to actually do it.
The moral equation is really very simple. It’s better to lose one life than three. We are so coddled we have forgotten that decisions of this type have been common throughout human history. We just refuse to accept it.