Ramu Perni, MD, MBA, explains UNITY's expanded Red Blood Cell Fetal Antigen noninvasive prenatal test

In February 2026, BillionToOne announced the launch of UNITY’s expanded Red Blood Cell (RBC) Fetal Antigen non-invasive prenatal test (NIPT), in addition to a first-and-only Platelet Fetal Antigen NIPT. The tests are designed to determine fetal antigen status in pregnancies affected by or at risk of hemolytic disease of the fetus and newborn (HDFN) and fetal and neonatal alloimmune thrombocytopenia (FNAIT).¹

In the video above, Contemporary OB/GYN spoke with Ramu Perni, MD, MBA, Medical Director, Prenatal, BillionToOne; board-certified sub-specialist in maternal-fetal medicine; American Board of Obstetrics and Gynecology, who discussed how the expansion of the UNITY Fetal Antigen NIPT is moving the specialty toward a more precise, evidence-based standard of care.

Benefits of non-invasive prenatal testing of red blood cell fetal antigens

“To take it a step back a little further, we know that with alloimmunization in general, the traditional monitoring and workflow presented quite a few challenges for patients, obstetricians, and maternal-fetal medicine [MFM] physicians,” said Perni. “This challenge essentially stemmed from the inability to reliably determine the fetal red blood cell antigen status early in pregnancy.”

UNITY, the name of BillionToOne’s product line, now includes the fetal antigen and platelet antigen tests as add-ons to the UNITY aneuploidy assay. “We advise using the Unity aneuploidy assay as a first-line product. If antibodies are identified on a routine antibody screen in pregnancy, the clinician can then add on the RBC antigen test,” Perni explained.

He stated that by determining RBC status, for example, if an antigen-negative test is observed, various parts of continued surveillance are not required.

“When we did not know the fetal RBC antigen status, we performed a lot of extra monitoring with maternal antibody titers and MCA Doppler waveforms. This [caused] a significant utilization of resources, can be anxiety-provoking for patients, and changes the workflow in both ob-gyn and MFM practices,” Perni pointed out. “Now, we can determine the fetal RBC antigen status—for up to 16 antigens—as early as 9 weeks of gestational age. This is massively important because when we know a fetus is antigen-negative and therefore not at risk for HDFN, all of that extra surveillance—monthly maternal antibody titers and frequent Doppler assessments—does not have to occur.”

According to BillionToOne, the 16 red blood cell antigens increase coverage to approximately 99% of antigens associated with HDFN.

JAMA Network Guideline on RBC alloimmunized pregnancy

Support for the use of a cell-free fetal DNA (cffDNA) to determine accurate fetal RBC antigen status is provided in a November 2025 clinical practice guideline published in JAMA Network Open, which was derived from a working group of MFM and obstetrics physicians.²

The first recommendations, which carried a “moderate” confidence label based on quality of evidence, stated, “We recommend the use of maternal cell-free fetal DNA to accurately determine the fetal red blood cell antigen status drawn after 10 weeks’ GA in pregnancies complicated by RhD, RhC, Rhc, RhE, Kell or Fy^a alloimmunization. This recommendation carried a 92.5% agreement.”

“This is a major, practice-changing guideline. It changes things for obstetricians, who may not need to refer these patients out, and for MFM physicians, who may not have to perform heightened surveillance,” said Perni. “Most importantly, it is best for patients and their families. In a situation with a high degree of anxiety and uncertainty, we can reassure the vast majority of patients very early on that there is nothing to worry about and that extra surveillance is not warranted.”

References:

1. BillionToOne announces dual launch of UNITY expanded red blood cell and platelet fetal antigen NIPTs, extending its leadership in setting the new standard in prenatal care. BillionToOne. Press release. Published February 9, 2026. Accessed April 6, 2026. https://www.prnewswire.com/news-releases/billiontoone-announces-dual-launch-of-unity-expanded-red-blood-cell-and-platelet-fetal-antigen-nipts-extending-its-leadership-in-setting-the-new-standard-in-prenatal-care
2. Moise KJ, Markham KB, Spinella PC, et al. A Clinical Practice Guideline for the Management of Pregnancy Alloimmunized to Red Blood Cell Antigens. JAMA Netw Open. 2025;8(11):e2544649. doi:10.1001/jamanetworkopen.2025.44649