What Is Fetal Viability?

You may have heard about the issue of fetal viability and you’ll be hearing a lot more about it over the next year, all on the context of the legal status of induced abortion in the United States. This is because the Supreme Court of the United States (SCOTUS) is now considering the a case called Dobbs versus Jackson Women’s Health Organization. This case involves the Jackson Women’s Health Organization, Mississippi’s only licensed abortion facility, and one of its physicians, challenging the “Gestational Age Act,” a Mississippi law that prohibits all abortions occurring subsequent to 15 weeks gestational age, with very few exceptions. The law represents an attempt by abortion opponents in Mississippi to get the SCOTUS to overturn the 1973 Roe versus Wade decision that established the right to an abortion within the realm of privacy guaranteed by the due process clause of the 14th Amendment and also is the basis of the trimester framework to which we refer so much here on The Pulse. Along with a recent Texas law seeking to enable anti-abortion activists to sue parties they presume to be involved in abortion, the Mississippi act that made it to SCOTUS is part of a plethora of laws passed in various states that have been cutting away at abortion rights, a trend that accelerated following the 1992 SCOTUS decision of Planned Parenthood versus Casey. As explained in our recent series on abortion, the 1992 case upheld the 14th Amendment aspect of Roe v. Wade, but changed the abortion landscape dramatically by dismantling the trimester framework, based on claim that the point of viability could be pushed back to significantly earlier in the pregnancy than the beginning of the third trimester. Since the Planned Parenthood v. Casey decision also upheld certain restrictions written into a Pennsylvania abortion law that had generated the case, the decision also has enabled various states to impose various restrictions, such as requiring women to jump through various hoops before they can get an abortion, or, incases of teens, to obtain permission from a parent.

While the third trimester generally is said to begin at 28 weeks of gestation, there has been some wiggle room dating back to the Roe era related to the idea of viability becoming reasonable around 26 weeks gestation. Opinions by a plurality of SCOTUS justices in the 1992 case that have come to be remembered as the “moderates” was that viability —and therefore restrictions on the right to an abortion— could be pushed back by a few weeks based on a few anecdotal cases of very young neonates surviving as a result of neonatal technology, including one case of a neonate surviving after birth at just 21 weeks and 5 days gestation. Even today, survival after such premature birth is exquisitely rare, but this did not stop the 1992 so called moderate plurality from declaring that it made scientific sense to push back legal viability well into the mid second trimester.

As noted above, viability depends mostly on lung maturity. One important factor in this realm involves soapy substances called surfactant. If you think about inflating a balloon by blowing into it, recall how it is very difficult to inflate at the beginning, when the balloon is small and less flexible, but it becomes easier as the balloon gets bigger. Think of the alveoli (air sacs) of lungs like balloons that can be easier or harder to stretch. Alveoli that have surfactant and the correct proportions of different types of surfactants are more like the balloon when it is big and stretched; they stretch more easily, so air can enter. Alveoli that lack surfactant are more like the balloon when it is small; it takes much more force to inflate them. By giving certain medications to the mother when preterm birth is anticipated, by spraying artificial surfactant into a preterm infant’s lungs, and by putting a preterm infant on mechanical ventilation or extracorporeal membrane oxygenation (ECMO) and using other neonatal intensive care measures, doctors can push back the natural limits of viability by a few weeks, but there is a limit that will not be pushed further —until there is an artificial placenta, a device that can maintain a preterm infant with its lungs deflated, maintaining the fetal circulation architecture in which blood bypasses the lungs and is oxygenated and freed of its carbon dioxide at the placenta.

Meanwhile, headed into 2022, neonates born much earlier than approximately the 24th week are still more likely to die than to live, since, despite research advances toward an artificial placenta or an artificial womb, such technology is probably decades away from clinical reality.

And yet, the Mississippi law makes abortion illegal at just 15 weeks, a point in pregnancy, when it is currently clinically impossible for a fetus to survive outside the mother. While various organ systems, such as the liver, will come into play in viability when technology eventually does start enabling some cases of survival prior to 21 weeks by way of artificial placenta technology, all discussions of viability up to this point in time center on the fetal/neonatal lungs, which are not ready to function at any point close to 15 weeks gestation. Nor is the fetal circulation ready to accommodate the out-of-womb scenario in which blood from the right side of the heart moves through the lungs and then returns to the left side of the heart to be pumped through the body. And so, laws like the Mississippi law that impose restrictions or completely prohibit abortion at earlier and earlier points in pregnancy are out of tune, even with the move against the trimester framework that came with Planned Parenthood v. Casey in 1992, and really have just one purpose: to make abortion so inconvenient for poor women who cannot afford to travel out of state that effectively they will have lost all rights to an abortion.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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