"The rhythm specified in the six-week abortion bans... 'is a group of cells with electrical activity. That’s what the heartbeat is at that stage of gestation… We are in no way talking about any kind of cardiovascular system.'"

"In part because that rhythm is a sign of the health of the developing embryo, scientists have worked to push backward the moment in pregnancy they can detect it. In 1984 they were pretty psyched to pick up fetal cardiac activity at between 41 and 43 days of gestation—six weeks. The researchers described it as a 'tiny blinking, flashing, and/or rocking echo with a regular rhythm... What’s really happening at that point is that our ultrasound technology has gotten good enough to be able to detect electrical activity in a rudimentary group of cells,' [said Sarah Horvath, an ob-gyn with the American College of Obstetricians and Gynecologists]. But if you’re thinking about this as something that looks roughly like a person with something that looks roughly like a chest, inside which something that looks roughly like a valentine is going pitter-pat (or lubdub-lubdub), you’re picturing the wrong thing. As the ob-gyn Jen Gunter wrote three years ago, this is, more technically, 'fetal pole cardiac activity.' It’s a cluster of pulsing cells. 'In the mouse embryo, for example, there is a definite cardiac rhythm in the tiny, little, immature heart at 8.5 days of development, but it is certainly not enough to support viability,' says Janet Rossant, senior scientist and chief of research emeritus at the Hospital for Sick Children in Toronto. 'It is just helping to encourage the development of an organized vasculature and circulatory system—a prerequisite for future viability but not sufficient alone.' That’s the other wobbly term of art here: 'viability.' In common parlance, people sometimes use that word to describe a baby far enough along in gestation to survive outside a woman’s womb. In humans, that takes about 24 weeks, give or take (every pregnancy is different, and so are the skill sets of every hospital and every neonatal intensive care unit). But that’s not what clinicians mean. 'It means a pregnancy that, at that point in time, looks like it’s normal to continue,' [says Jennifer Kerns, an ob-gyn at UC San Francisco]."

From "'Heartbeat' Bills Get the Science of Fetal Heartbeats All Wrong" (Wired).

Quite aside from the meaning of "heartbeat," there's the meaning of "viability"? "Heartbeat" hasn't been a significant term in the constitutional analysis of abortion restrictions, but "viability" is one of the most important concepts, and it hasn't been what Kerns says clinicians means — that a pregnancy looks like it’s normal to continue.

What the article calls "common parlance" — using the word to refer to the ability to survive outside a woman’s womb — is also the definition in the legal cases. It's the point at which the woman's right to choose not to be pregnant ends, and the state may choose to override her freedom. It's hard to understand why that sort of viability became the legal line, because denying the abortion means that the unborn remains inside the womb. But that was a line that was identified by the Court long ago, and maybe some day the Court will look at that idea of capacity to survive outside the womb and say that it's not where the line should be.

"Heartbeat" is another concept, and it could be embraced as the right place to draw the line, and I wonder if the argument for doing that is enhanced by the fact that clinicians are using the word "viability" to refer to that point. It seems that the clinicians are using the word that way because it makes for good doctor-patient relations. For a woman who is hoping for a child, it's reassuring and encouraging. The same thing is true of the word "heartbeat."

But it's quite another thing to take this science — detecting early cellular rhythm and forming a belief that normal development is happening — and to use it to make a statute that restricts the freedom of women who do not want to be pregnant.