With the first four installments of Chapter 2 covering diagnostic genetic testing, we now turn to prenatal genetic screening. The previous installments can be found here. Read on to learn how a lawsuit, not science, changed the standard of care for prenatal genetic testing for Down syndrome.
C. Prenatal genetic screening for Down syndrome
In the 1980’s, researchers noticed there was a correlation to the amount of alpha-feto protein (“AFP”) found in the expectant mother’s bloodstream and open neural tube defects (“ONTB”), like spina bifida. The higher the AFP level, the higher the chance the pregnancy may be affected with an ONTB. For this reason, AFP was recognized as what is called a “prenatal screen” or “screening test.”
With screening tests, a result indicating a higher chance for the screened-for condition does not mean that the fetus definitively has the screened-for condition—only that there is an increased chance for the condition. Screening tests have false negatives, i.e. a screen may indicate a reduced probability for a condition when, in fact, the fetus has the screened-for condition. Conversely, a false positive is when a screen result indicates an increased chance, but the child is unaffected. Due to every screening test being “screens,” none of them are diagnostic. Whatever the screen result, increased chance or reduced chance, expectant parents can only know for sure from prenatal diagnostic testing discussed in the immediate preceding section … or wait until the child is born.
Back to AFP, it was further noticed that there was an inverse correlation between AFP and the incidence of Down syndrome: a lower than expected AFP level could mean an increased chance for Down syndrome. The correlation, however, was not as strong as the direct relationship between AFP and ONTDs. The FDA refused to recognize AFP as an accurate screening test for Down syndrome.
And, then a baby was born in California that happened to have Down syndrome.
The surprised parents learned of the research showing something of a relationship with AFP and Down syndrome and sued their obstetrician. Their complaint was that the obstetrician, despite AFP specifically not being recognized by the FDA as accurate enough to screen for Down syndrome, was nonetheless negligent in caring for their pregnancy. The parents claimed that had they known they could have had an AFP test and it showed lower than expected levels, which suggested a possible increased chance for Down syndrome, then they would have aborted their child. Having missed out on their opportunity to avoid the claimed increased lifelong costs for caring for their child with Down syndrome, their obstetrician was liable to cover those additional costs.
The parent’s odious and illogical legal claim–referred to as a “wrongful birth” lawsuit, which will be examined further in the next chapter–survived the obstetrician’s legal team’s defenses and the parents were awarded a judgment. As a result, ACOG issued its first ever “Liability Alert,” instructing its members to not only offer AFP testing to all women 35 and older, but to document in their patients’ charts that the offer had been made and what decision their patients made. Screening testing for Down syndrome was ushered in not based on scientific evidence or clinical utility; Down syndrome prenatal screening became the standard of practice because of a lawsuit.
Initially, AFP remained the only recognized prenatal screen for Down syndrome. In the following years, additional proteins and biomarkers in the mother’s blood stream were identified: human chorionic gonadotropin (HCG), estriol and inhibin A. When measurements of these markers along with AFP were processed through a laboratory algorithm, it provided a more accurate assessment of the likelihood that the pregnancy was affected by an ONTB or Down syndrome. With three factors being analyzed in addition to AFP, the screen became known as the “Quad screen.”
The Quad screen, however, could only be offered in the second trimester. Being a screening test, diagnostic testing then is needed to confirm its results, if the parents wish to know for certain whether their fetus has the screened-for condition or not. With Quad testing, if the couple begins with prenatal screening offered in the second trimester, days elapse for the lab results. If the parents want to know for sure, they then must have an amnio, and again days pass (in the ‘80’s and ‘90’s, it could be weeks), for the amnio’s results to be reported. All this waiting, and potentially running out of time if the parents choose the option discussed in the next chapter, remained a point of frustration for some researchers and practitioners.
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