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Setting the record straight on measuring fetal age and the ’20-week abortion’

(AFP Photo/Mandel Ngan)

“In no way, shape or form is a 20-week fetus viable. There’s no evidence of a 20-week fetus surviving, even with intensive medical care.”

–American Congress of Obstetricians and Gynecologists Executive Vice President Hal Lawrence, quoted in a news article, May 13, 2015

Several readers requested The Fact Checker to examine claims related to the Pain Capable Unborn Child Protection Act, recently passed by the House. This bill is commonly referred to as the “20-week abortion ban.”

The abortion debate is fraught with rhetoric that cannot be easily fact-checked. But a reader pointed us to the quote above and asked whether a new study on the viability of 22-week fetuses can be applied to 20-week fetuses, when using a different method to count gestational age. To add to the confusion, states vary in their definitions for gestational age. The quote above is one example of several instances in recent media coverage that related to definitions of gestational age.

This is a technical, but important, part of the bill. The little-known difference between two methods of counting gestational age is contributing to inconsistent media coverage, and could mislead the public, parents and providers about the bill’s provisions.

So what exactly is going on?

The Facts

The Pain Capable Unborn Child Protection Act bans late-term abortions after the midpoint of a woman’s pregnancy, and before the fetus typically is considered viable to live outside of the womb. The age of viability has been pegged at 24 to 28 weeks. Proponents argue an abortion ban at younger than 24 weeks, saying fetuses can feel pain before then — a claim based in complex science and disputed by the Royal College of Obstetricians and Gynaecologists. (Supporters point to various studies related to fetal development, compiled here.)

A new study published in the New England Journal of Medicine on May 7 examined how hospitals differ in whether and how they treat extremely premature babies, starting at 22 weeks. Proponents of the bill say this study, funded by the National Institutes of Health, shows that the babies who would be saved through the 20-week abortion ban could now be considered viable. Some media reports also echoed the same conclusions.

Sound confusing? The distinction is this: The bill defines the age of the fetus as “post-fertilization age,” calculated from the moment of conception. This is different from the widely-accepted definition used by medical professionals and the Centers for Disease Control and Prevention, counting the fetus age from the first day of the pregnant woman’s last menstrual period (“LMP”).

Fertilization typically happens about two weeks after the first day of LMP. The idea is that it is difficult to know exactly when you became pregnant, but you know when you started your last period. That is why the bill’s supporters say the 20-week age measured from fertilization essentially is the LMP-measured age of 22 weeks.

The bill’s definition is a more technical and accurate measure, said Michael Woeste, House Judiciary Committee spokesman. He noted an excerpt in The Developing Human: Clinically Oriented Embryology, arguing that the LMP method is error prone partly because “it depends on the mother’s memory of an event that occurred several weeks before she realized she was pregnant” and that “the day fertilization occurs is the most accurate reference point for estimating age.”

Lawrence’s quote at the top of this fact check comes from a statement during a recent media call. (The American Congress of Obstetricians and Gynecologists, or ACOG, opposed the bill.) He was referring to the 20-week LMP age, not the 20-week post-fertilization age.

The rest of his statement during the call explains his point further and how it ties in with the legislation (and also wrote an op-ed about it in Time):

Now, I’d like to talk a bit about why supporters of a 20-week abortion ban are, quite simply, wrong. There is no medical milestone associated with 20 weeks. Gestation is a gradual process, and it can vary depending on the circumstances, such as the woman’s health.
But still, even accounting for this, the 20-week mark is just not notable from a fetal development standpoint. More than 40 years ago, the Supreme Court stipulated that abortion is legal until a fetus is viable. Well, in no way, shape or form is a 20-week fetus viable. There is no evidence anywhere of a 20-week fetus surviving, even with intensive medical care.
Unfortunately, some advocates of abortion bans are pointing to a new study, just published last week, that they claim heralds 22 weeks as being the new point of viability. They suggest that we might someday reach viability at 20 weeks. It is essential that we address that now, before this becomes another myth about abortion that is accepted as reality.

We spoke with the main authors of the study, Matthew Rysavy and Dr. Edward Bell of University of Iowa. They collected data for nearly 5,000 infants born between 22 and 27 weeks of gestation (using LMP method) and did not have abnormalities at birth. These babies are extremely pre-term, as full term is considered at 39 to 40 weeks, according to ACOG guidelines.

Researchers found that 22 percent of the babies born at 22 weeks received active treatment, and hospitals varied in their whether and how they gave treatment to babies born between 22 and 27 weeks. There were 78 babies born at 22 weeks who received aggressive treatment. Among them, 18 of them survived (23 percent) to toddler age. Seven (9 percent) of them did not have severe or moderate impairment by the time they were toddlers.

That babies can survive at 22 weeks is not a new finding; it has been known for 15 years, Rysavy said. The point of the study was to highlight differences in practices and outcomes between hospitals, he said. Many factors, including gestational age, influence how well a baby does: “Our paper wasn’t exactly intended for identifying which infants would do well.”

The Fact Checker asked if, using the “post-fertilization” age definition in the bill, their findings can carry over to babies at 20 weeks old from the point of conception. Bell and Rysavy said that would be “terribly confusing” to the public, pregnant women and even to politicians. Bell said the LMP method is used around the world, and that the time of conception accurately cannot be ascertained.

“You cannot redefine gestational age based on conception. … The new terms are politician terms. They have no relevance at all to medicine or biology. They’re just going to confuse everybody,” Bell said. “They have the right to do that for the purpose of making laws, but to me, it just looks like an attempt to obfuscate and create confusion. We already have a well-established definition of the length of pregnancy that has worked just fine, for generations, has been used forever.”

Rysavy also sent us this diagram, of the American Academy of Pediatrics’ terminology for age during the perinatal period:

ACOG recommends using LMP and updating the due date with other measures, such as ultrasounds, since women may have irregular cycles and there is variability in how long a fertilized egg becomes implanted in the uterus (thus beginning pregnancy). Lawrence, in a statement, said: “The fact that federal legislation is basing restrictions on reproductive care based on a non-medical calculation of pregnancy is evidence of what happens when lawmakers try to legislate women’s health.”

The Bottom Line 

New research confirmed that 22-week fetuses, measured from the first day of the pregnant woman’s last menstrual cycle, can survive. Babies born before that age did not survive. So, Lawrence is correct that 20-week fetuses, measured from the first day of the pregnant woman’s last menstrual cycle, are not viable. He is incorrect when using the definition in the Pain Capable Unborn Child Protection Act.

The Fact Checker takes no stance on which definition should be used. However, we want to set the record straight for the public and the media. This is a technical point over how gestational age is calculated. But it is important, as it has contributed to some misleading headlines, lack of context in news coverage and general confusion in the public debate. It also has contributed to the rhetoric on both sides; the difference between the two definitions has not been clear in much of the news reporting.

In many way, the debate is similar to how budget figures can vary dramatically depending on the baseline that is used. Reporters need to specify exactly what method of measuring the pregnancy is being used, as the difference is not trivial.

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