Laboratory Mistake Yields Inaccurate Report for Woman Pregnant With Down Syndrome Baby

The OBGYN employed proper screening with the exception of the triple screen. There was a quality control failure where the result cutoff was set at 1 in 300 instead of the standard 1 in 270. Therefore, there was no abnormal screening reported to the physician. Had the cutoff been appropriately set, the mother would have been given the choice of termination.

Question(s) For Expert Witness

1. Is the above situation a quality control failure by the laboratory?

Expert Witness Response

Screening markers are used to calculate a pregnant woman's risk of having a child with Down syndrome, thereby allowing her to make an informed choice about invasive diagnostic testing, which is costly and associated with some risk of pregnancy loss. A variety of serum markers are used to screen for Down syndrome in the first and/or second trimesters. The quad test is performed in the second trimester (optimally at fifteen to eighteen weeks of gestation) and consists of alpha fetoprotein (AFP), unconjugated estriol (uE3), human chorionic gonadotropin (beta-hCG), and inhibin A (inhA) measurements. Each patient should be given the specific numerical risk of Down syndrome (eg, 1 in 100) calculated for her based on her age and screening test results. The risk cut-off chosen for test interpretation (ie, identifying patients as screen negative or screen positive) determines the detection and false positive rates for Down syndrome. For a given test, as the risk cut-off gets higher, fewer women are screen positive and fewer affected pregnancies will be identified. If less stringent risk cut-offs are chosen, a greater number of affected pregnancies will be identified, but there will be more false positive tests leading to a larger number of couples experiencing parental anxiety and having to consider costly and potentially risky diagnostic procedures. Thus, there is always a trade-off between an optimal detection rate and a tolerable screen positive rate.