Rallybio Terminates Phase 2 FNAIT Pregnancy Study: What Investors Need to Know

Rallybio Corporation (RLYB) announced an update on their ongoing clinical study.

Rallybio’s latest update centers on a Phase 2, multicenter, open-label study titled “A Phase 2, Multicenter, Open-label Study to Evaluate the Pharmacokinetics and Safety of RLYB212 in Pregnant Women at Higher Risk for HPA-1a Alloimmunization.” The study aims to understand how the drug moves through the body and how safe it is for pregnant women at higher risk of developing antibodies that can lead to fetal and neonatal alloimmune thrombocytopenia (FNAIT), a rare but serious condition. While technical in scope, the big-picture goal is to support a preventive option that could lower risk for affected pregnancies.

The study’s intervention is RLYB212, delivered as a subcutaneous (under the skin) injection. RLYB212 is an anti–integrin beta-3 human monoclonal antibody designed to target a specific platelet antigen (HPA-1a). The intent is to prevent or reduce the immune reaction in at-risk pregnant women that can harm the baby’s platelets and lead to bleeding complications.

The trial is interventional, meaning it actively tests a treatment rather than just observing patients. All participants are assigned to a single treatment group that receives RLYB212, so there is no placebo or comparison arm. The study uses an open-label design, which means both doctors and participants know they are getting the drug. The primary purpose is prevention, focusing on safety signals and how the drug behaves in the body rather than direct clinical outcomes like bleeding events at this stage.

The study was first submitted on May 21, 2024, marking the formal start of its regulatory and operational timeline. The most recent update was posted on January 12, 2026, indicating the sponsor has refreshed the listing and study information. The current overall status is listed as “Terminated,” meaning the trial stopped earlier than planned. This status is important for investors because it signals a change in development trajectory and may alter future timelines and costs for the program.

For Rallybio (RLYB), the termination of a Phase 2 study in a key maternal-fetal program can weigh on near-term sentiment and introduce doubts about the path forward for RLYB212, even before full data are public. Investors will watch closely for the reasons behind the termination—whether they relate to safety, feasibility, enrollment, or company strategy—as these details will shape the valuation impact. In the broader rare-disease and maternal-fetal health space, setbacks can shift attention and capital toward competitors working on FNAIT and similar conditions, but they can also highlight the high barriers to entry and potential long-term value for any player that eventually succeeds. This study has been updated and is now terminated, with further details available on the ClinicalTrials portal.

To learn more about RLYB’s potential, visit the Rallybio Corporation drug pipeline page.