New Study Showed Unnecessary Burden From Continued Monitoring of Alloimmunized Pregnancies With Antigen-Negative Fetuses

New research demonstrates that monitoring with titers frequently leads to burdensome and unnecessary monitoring for pregnancies not at risk of hemolytic disease of the fetus and newborn (HDFN)

MENLO PARK, Calif., Oct. 10, 2025 /PRNewswire/ -- BillionToOne, Inc., a molecular diagnostics company with a mission to create powerful and accurate tests that are accessible to all, today announced a new publication in Pregnancy titled, High frequency of critical and rising titers in alloimmunized pregnancies with antigen-negative fetuses¹. The study validates the clinical utility of fetal antigen cell-free DNA (cfDNA) testing and demonstrates how traditional antibody titer monitoring can lead to unnecessary monitoring and interventions in pregnancies that cfDNA testing determines are not at risk for hemolytic disease of the fetus and newborn (HDFN, a blood disorder).

Fetal antigen cfDNA testing offers a transformative alternative to current monitoring practices and is available for use as early as the ninth week of pregnancy. Previous studies published in Obstetrics & Gynecology and Scientific Reports demonstrated 100% concordance between BillionToOne's fetal antigen testing and neonatal outcomes across 186 total alloimmunized pregnancies^2,3, providing strong evidence that when a fetus tests antigen-negative, the result is accurate and can be relied on for guiding patient care, including discontinuing monitoring of these pregnancies.

This study of 69 pregnancies revealed significant downstream consequences to monitoring with titers when cfDNA has already determined the fetus is antigen negative and therefore not at risk of developing HDFN. Consistent with previous studies, all fetal antigen cfDNA results in these 69 patients were confirmed postnatally, indicating 100% accuracy of BillionToOne's fetal antigen testing. However, in this study, downstream clinical practices were also analyzed. While the usage of serial titers and middle cerebral artery peak systolic velocity (MCA-PSV) Doppler were decreased in the pregnancies identified as fetal antigen-negative, despite cfDNA results, 69% and 62% of fetal antigen-negative patients underwent serial titer monitoring and MCA-PSV Doppler, respectively. Remarkably, 50% of the fetal antigen-negative pregnancies showed rising antibody titer levels over time, prompting additional monitoring and interventions, with one patient receiving a false positive MCA-PSV Doppler result suggesting fetal anemia. Another patient underwent amniocentesis despite receiving negative fetal antigen cfDNA results, because rising titers led to concern for a risk for fetal anemia. Amniocentesis confirmed the fetus was antigen-negative, as originally determined noninvasively by cfDNA testing.

The study also showed that standard antibody titers reached critical levels in 69% of pregnancies even when the fetus was antigen negative, virtually identical to the 70% rate seen in pregnancies where the fetus was antigen positive. Critical and rising titers can trigger intensive monitoring and even invasive procedures to assess for fetal anemia, as seen in antigen-negative pregnancies in this study, despite these fetuses having no expected risk of developing HDFN. Unnecessary monitoring and interventions pose burdens and risks, including the potential for additional antibody sensitization, as well as significant time and financial costs for both the patient and healthcare system.

"The research in this study highlights a critical gap in current clinical practice, where traditional antibody screening methods fail to distinguish between pregnancies that truly require intensive monitoring and those that do not," said Dr. Haywood Brown, Chief Medical Officer, Prenatal at BillionToOne. "Our UNITY Fetal Antigen NIPT provides the precision needed to identify which pregnancies are actually at risk for HDFN, allowing us to spare families from unnecessary anxiety and procedures while ensuring appropriate care for those who need it."

The findings are particularly relevant given recent updates to clinical guidance. In August 2024, the American College of Obstetrics and Gynecologists (ACOG) issued updated recommendations acknowledging that fetal antigen cfDNA "may be considered" for pregnant patients declining amniocentesis, representing a shift toward incorporating this technology into standard of care.

The study data suggest that for alloimmunized pregnancies carrying antigen-negative fetuses, fetal antigen cfDNA testing could potentially eliminate the need for months of intensive monitoring while maintaining excellent clinical outcomes.

About BillionToOne
Headquartered in Menlo Park, California, BillionToOne is a molecular diagnostics company with a mission to create powerful and accurate tests that are accessible to all. The company's patented Quantitative Counting Templates™ (QCT™) molecular counting platform is the only multiplex technology that can accurately count DNA molecules at the single-molecule level. For more information, visit www.billiontoone.com.

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¹  Balogun, Olaide Ashimi, et al. 2025. High frequency of critical and rising titers in alloimmunized pregnancies with antigen-negative fetuses. Pregnancy.
² Rego, S., Ashimi Balogun, O., Emanuel, K., Overcash, R., Gonzalez, J. M., Denomme, G. A., Hoskovec, J., King, H., Wilson, A., Wynn, J., & Moise, K. J. (2024). Cell-Free DNA Analysis for the Determination of Fetal Red Blood Cell Antigen Genotype in Individuals With Alloimmunized Pregnancies. Obstetrics and Gynecology. https://doi.org/10.1097/AOG.0000000000005692
³ Alford B, Landry BP, Hou S, Bower X, Bueno AM, Chen D, Husic B, Cantonwine DE, McElrath TF, Carozza JA, Wynn J, Hoskovec J, Gray KJ. Validation of a non-invasive prenatal test for fetal RhD, C, c, E, K and Fya antigens. Sci Rep. 2023 Aug 7;13(1):12786. doi: 10.1038/s41598-023-39283-3. PMID: 37550335; PMCID: PMC10406947.

SOURCE BillionToOne