I. Glenn Cohen is an assistant professor at Harvard Law School and co-director of the Petrie-Flom Center for Health Law Policy, Biotechnology, and Bioethics.

On Thursday, Arizona’s new abortion law will take effect, outlawing the procedure after 20 weeks of pregnancy — a much earlier threshold than in any other law that has been upheld in court. Like-minded laws have been enacted in Nebraska, Alabama, Idaho, Indiana, Kansas, Oklahoma, Georgia and Louisiana, and a bill similarly limiting abortion in the District drew support Tuesday from a majority of the U.S. House, but not from enough members to pass.

These measures differ from previous attempts to prohibit abortion in that they rely on both the scientific claim that a fetus is capable of feeling pain and the legal claim that states may prohibit abortions to prevent that pain.

Although these laws rely on dubious medical science, they aim to exploit a loophole in the law and tempt federal judges disposed against abortion rights to find them constitutional. Thus, the laws present a major threat to abortion rights as we know them.

Since Roe v. Wade, the Supreme Court has consistently held that the Constitution permits states to prohibit abortion (as opposed to limiting the procedure used) only in order to preserve fetal life after the fetus is capable of surviving outside the womb. In constitutional law parlance, only at this viability point does the state’s interest in preserving fetal life become “compelling.”

Most medical professionals agree that viability begins at 23 to 24 weeks into pregnancy. These recent laws, then, represent an attempt to prohibit abortion before this threshold.

The fetal-pain bills do not directly challenge the Supreme Court’s judgment. Instead, they assert a new theory for outlawing abortion. The Nebraska bill states that “by twenty weeks after fertilization there is substantial evidence that an unborn child has the physical structures necessary to experience pain.” The legislatures passing these laws say that preventing this pain is a compelling state interest that justifies prohibiting abortion.

Hence, the loophole: Although the Supreme Court has identified preserving fetal life after viability as a compelling interest, the justices have never said it is the only one.

These statutes might be thought of as asking the courts to find that preventing pain to fetuses is also a compelling state interest. Alternatively, states may argue that, although preventing pain is not compelling on its own, it becomes so when combined with the state’s interest in preserving fetal life before viability.

Whichever variant is adopted, the argument is flawed.

First, medical and psychological research shows that pain is both a physical response and an experiential one. The neural structures that a fetus would need to “experience” pain do not develop until well beyond the point at which these bills prohibit abortion. It is this experience of pain — not the observable neuroendocrine, metabolic and reflexive responses to stimuli to which these bills point — that matters in terms of the state’s interest. Thus, these bills are based on a false construct.

Second, even if fetal pain existed, the alleged experience could be prevented without outlawing abortion. As proof that fetuses are capable of feeling pain, Nebraska’s law notes that physicians often administer anesthesia to fetuses. This is done to relax muscles or to prevent neurodevelopmental problems later on — not, medically speaking, to control pain. But if these fetuses were capable of feeling pain, administering anesthesia would likely prevent any sensation of pain, just as it does in children and adults. Thus, there is no legal reason to prohibit abortion at 20 weeks: We can prevent fetal pain during an abortion — without burdening a woman’s right to that abortion — by requiring the administration of anesthesia to the fetus.

Even if such bills could overcome both objections, states still have not shown why their interest in avoiding the allegedly real and unavoidable experience of fetal pain should outweigh a woman’s right to an abortion. Although fetal pain might be relevant to that calculation, perhaps changing which abortion procedures are performed, it is not clear why it should be dispositive.

Because these laws are scientifically and legally ill-founded, federal courts should strike them down. Nevertheless, defenders of abortion rights should be afraid. Because such legislation invites courts to further restrict abortion without overruling existing precedent, it is entirely possible that they will garner five votes on the current Supreme Court and change the face of abortion law as we know it.