Critical Thinking About Preterm Survival Rates

So, I’ve been vaguely aware of lots of claims that survival of babies born before 24 weeks has dramatically improved recently. This matters because the current standard UK cut-off for abortions is 24 weeks. (Later abortions are permitted in special circumstances.) The forced-childbearing lobby (considerably weaker in the UK than in the US) is making heavy use of these claims of better survival before 24 weeks to argue for an earlier cut-off. The Guardian’s excellent Bad Science column does a beautiful job on these claims of increased early survival rates. First, these claims represent a distinctly minority viewpoint:

Scientific and medical expert bodies giving evidence [before the parliamentary committee] say that survival in births below 24 weeks has not significantly improved since the 1990s, when it was only 10-20%. But one expert, a professor of neonatal medicine, says survival at 22 and 23 weeks has improved. In fact, he says survival rates in this group can be phenomenally high: 42% of children born at 23 weeks at some top specialist centres. He is quoted widely: the Independent, Telegraph, on Newsnight, by Tory MPs, and so on. The figure has a life of its own. 

The key to understanding the 42% claim is that it matters which babies are being looked at. Is it 42% of babies born alive, or 42% of babies admitted to intensive care? As Ben Goldacre writes,

To be admitted to neonatal ICU, the doctors have to think you’ve got a chance. Often you have to be transferred from another hospital, in an ambulance, and for that you really do have to be more well. Therefore, if your denominator is “neonatal ICU admissions”, your survival rates will be higher, but you are not comparing like with like. 

A bit of searching around reveals that the apparent increase in 23 week survival was due to looking not at all babies born alive (the relevant figure if what you’re wondering is how well babies at this age can survive outside the womb), but rather all babies admitted to intensive care.This is a really important distinction, and very likely to be important in discussions outside the UK as well.

5 thoughts on “Critical Thinking About Preterm Survival Rates

  1. I had a quick look at Gazzaniga’s The Ethical Brain, because I thought there might be support for your position. He seems to have written the book as a reaction to his experiences on our President’s bioethics council, out of which he seems to have emerged really very angry.

    (For people who don’t recognize the name, he’s a big-time neuroscientist who favors a lot of things feminist typically do about abortion and stem cell research. He’s also just gotten a huge grant to work on neuroscience and the law.)

    He says that 23 weeks is the cut-off time, and after that the fetus can survive. He also says that that’s the date the supreme court has set as a limit on abortion.

  2. But the key question is what’s meant by “can survive”? What sort of survival rate is needed to support it?

  3. I wasn’t clear enough, I think. I just meant to point out that agreement on the other side of the pond seems to have converged on an earlier date.

    Gazzaniga is pretty dismissive of the problems of survival,and says something like its easy if there’s medical intervention. I expect he’s concentrating on the condition of the brain; it’s hard to believe that anyone would say that the lungs are easily sustained.

  4. So, current status of medicine aside, as technology advanced the date will tend towards conception? That doesn’t sound right.

  5. I vaguely remember conjectures about artificial wombs. Perhaps if they are developed, the pro-lifers will start to insist that all those frozen embryos get developed.

    I wish that there was some way to connect votes with responsibility for enacting the laws. As in: OK, you want war, your children can join those fighting. Or, OK, you want these embryos developed into human beings, go put an addition on your house and prepare to be taking care of them.

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