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Poster Session 4

Category: Fetal Intervention

Poster Session 4

(1096) Antibody titers rise after transplacental IUT: a hypothesis-generating study

Thursday, February 12, 2026

3:30 PM - 5:00 PM

Submitting Author and Presenting Author(s)

Giulia Bonanni, MD

Postdoctoral Research Fellow
Division of Fetal Medicine and Surgery, Boston Children's Hospital Harvard Medical School
Boston, Massachusetts, United States

Coauthor(s)

EH

Emily Hutson, MSN, RN

Research Associate/Clinical Outcomes & Quality Data Specialist
Department of Women’s Health, Dell Medical School at the University of Texas at Austin
Austin, Texas, United States
EM

Erin E. Moise, PA-C

Research Associate / Clinical Outcomes & Quality Data Specialist
Department of Women’s Health, Dell Medical School at the University of Texas at Austin
Austin, Texas, United States
Alireza A. Shamshirsaz, MD (he/him/his)

Department Director, Professor of Surgery
Boston Children's Hospital, Harvard Medical School
Boston, Massachusetts, United States
Kenneth J. Moise, Jr., MD (he/him/his)

Co-Director, Comprehensive Fetal Care Center; Prof, Women’s Health
Department of Women’s Health, Dell Medical School at the University of Texas at Austin
Austin, Texas, United States

Objective:
To evaluate whether transplacental intrauterine transfusion (IUT) increases maternal alloantibody production. We hypothesized that transplacental IUT enhances maternal exposure to fetal red blood cell (RBC) antigens, increasing the degree of alloimmunization (Fig. 1).

Study Design:
We retrospectively reviewed patients undergoing IUT for RBC alloimmunization at a single center. The primary exposure was placental location (anterior vs posterior), which informs procedural approach and risk of transplacental needle passage. To refine exposure classification, procedural videos were reviewed to confirm whether the needle traversed the placenta, enabling a second exposure definition: verified transplacental vs non-transplacental. A titer increase was defined as any rise in antibody titer between the pre-IUT#1 and the next available post-IUT value. Statistical analyses included Fisher’s exact test and t-tests. Clinical relevance was assessed using Number Needed to Harm (NNH), and power calculations were performed to estimate sample size needs for future studies.

Results:
Among 28 patients, a titer increase occurred in 7/10 (70%) anterior vs 5/18 (28%) posterior placentas (OR 5.63, 95% CI 0.86–48.5, p=0.05; Δlog₂ titer: 1.20±1.03 vs 0.22±1.31, p=0.04). When reclassified by observed transplacental entry, a rise occurred in 8/14 (57%) vs 4/14 (29%) (OR 3.19, 95% CI 0.55–21.7, p=0.25). NNH was 2.5 (95% CI: 1.5–35.1) for anterior placenta and 3.6 (95% CI: 1.6–9.5) for transplacental approach (Table 1).

Conclusion:
Anterior placentation was associated with a higher risk of increase in alloantibody titer after the first IUT. A similar, though non-significant, trend was observed with confirmed transplacental entry. Power analysis suggests 56 patients are needed to detect the observed titer difference, and 92 for a binary outcome. These findings inform IUT counseling and support the need for a larger prospective study. If confirmed, rising titers may justify adjusting the interval between first and second IUT due to the potential for more rapid decline in fetal hematocrit secondary to enhanced alloimmunization.