I think many [anti]-choicers believe that ending a pregnancy to save the woman's life is justified

The official position of the Catholic Church, which has over a billion adherents, is that it is not. They lauded Nicaragua's decision to ban abortion without exception (previously it was banned with medical exceptions) after Daniel Ortega was elected. When Amnesty International declared that abortion was a human right in cases when the pregnancy put the mother's health at risk, the Church hierarchy said that Catholics should stop supporting the organisation. Of course, most Catholics ignore those teachings of the Church that strongly conflict with their own personal beliefs, so I couldn't say that all Catholics hold this position.

Perhaps more disturbing is the fact that, according to Gallup polls, the proportion of the population who think that abortion should be "illegal in all circumstances" generally stays in the 15-20% range. Assuming that all of those people describe themselves as "pro-life" in the same polls (a reasonable belief, I think), that's between 30 and 45 per cent of all anti-choicers who think abortion should not be allowed when the mother's life is at risk.

it would be good to see some cooperation on that front.

This is not going to happen, because anti-choicers are not actually interested in protecting the lives of fetuses. At every opportunity, they attempt to block measures that can improve women's health and reduce the number of abortions. The most recent example is the House bill passed the other day to defund Planned Parenthood. Taxpayer money is already prohibited from being used to fund abortions, so the funding that Planned Parenthood got was used to pay for things like the millions of contraceptives handed out each year, and the millions of cancer screenings and STI tests performed. If you take anti-choicers at face value when they say that they are concerned about the life of fetuses, I am afraid you are hopelessly naive.