Cell-Free DNA Testing Delivers 100% Accuracy for Early Fetal Genotyping for Alloimmunized Pregnancies: Study

"We found that cell-free DNA analysis is a highly effective tool for determining fetal red blood cell antigen genotypes in individuals with alloimmunized pregnancies. This breakthrough comes from a diverse cohort and highlights the test’s high sensitivity and specificity, even at just ten weeks of gestation," the researchers wrote.

Alloimmunization occurs when a pregnant person’s immune system produces antibodies against fetal blood antigens that are different from their own, potentially leading to complications such as hemolytic disease of the newborn. Traditional methods for determining fetal antigen genotypes often involve invasive procedures or can be less accurate early in pregnancy. However, the new cell-free DNA analysis offers a non-invasive and reliable alternative.

Against the above background, Kenneth J. Moise, MD, Department of Obstetrics and Gynecology, Department of Women's Health, Dell Medical School, Austin, TX, and colleagues assessed the accuracy of next-generation sequencing-based quantitative cell-free DNA analysis for fetal antigen genotyping in individuals with alloimmunized pregnancies, the study aims to evaluate its clinical use across practices in the United States. Conducted as early as 10 weeks of gestation, the objective is to identify pregnancies at risk for hemolytic disease of the fetus and newborn and to guide appropriate management strategies.

For this purpose, the researchers conducted a prospective cohort study involving patients with alloimmunized pregnancies who underwent clinical fetal antigen cell-free DNA analysis at 120 clinical sites between 10 0/7 and 37 0/7 weeks of gestation. The study included both the pregnant individuals and their resulting neonates.

The laboratory provided cell-free DNA results as part of routine clinical care. Following delivery, neonatal buccal swabs collected within 270 days of birth were sent to an independent laboratory for antigen genotyping. This external laboratory, blinded to the initial fetal cell-free DNA results, compared its findings with those from the fetal analysis. Concordance rates were reported for fetal antigen genotyping where the pregnant individual was alloimmunized, and for antigens where the pregnant individual was genotype negative.

The study led to the following findings:

• One hundred fifty-six pregnant individuals who underwent clinically ordered cell-free DNA fetal antigen testing were provided neonatal buccal swabs for genotyping after delivery. The participant demographics were as follows: 15.4% Hispanic, 9.0% non-Hispanic Black, 65.4% non-Hispanic White, 4.5% Asian, 1.3% identified as more than one race or ethnicity, and 4.5% had unknown racial or ethnic backgrounds.
• The median gestational age at the time of testing was 16.4 weeks, with a median fetal fraction of 11.1%.
• Concordance between cell-free DNA analysis results and neonatal genotype was determined for 465 antigen calls for the following antigens: K1 (n=143), E (124), C (60), Fya (50), c (47), and D(RhD) (41). These 465 calls included 145 in which the fetus was antigen positive and 320 in which the fetus was antigen negative.
• There was a complete concordance between prenatal fetal antigen cell-free DNA analysis results and neonatal genotypes for the 465 calls, resulting in 100% sensitivity, specificity, and accuracy.

In a diverse multicenter cohort, cell-free DNA analysis is highly sensitive and specific for determining fetal antigen genotypes as early as ten weeks of gestation in individuals with alloimmunized pregnancies.

"Combined with existing evidence, this study advocates for the adoption of cell-free DNA testing in managing alloimmunized pregnancies across the United States," the researchers concluded.

Reference:

Rego, Shannon MS; Ashimi Balogun, Olaide MD; Emanuel, Kirsten MS, FNP; Overcash, Rachael MD; Gonzalez, Juan M. MD, PhD; Denomme, Gregory A. PhD; Hoskovec, Jennifer MS; King, Haley MS; Wilson, Ashley MS; Wynn, Julia MS, MS; Moise, Kenneth J. Jr MD. Cell-Free DNA Analysis for the Determination of Fetal Red Blood Cell Antigen Genotype in Individuals With Alloimmunized Pregnancies. Obstetrics & Gynecology ():10.1097/AOG.0000000000005692, July 25, 2024. | DOI: 10.1097/AOG.0000000000005692