Alloimmunized individuals who undergo transplacental intrauterine transfusion (IUT) may experience elevated antibody titers, according to a poster presentation at the 2026 Society for Maternal-Fetal Medicine meeting.
Hemolytic disease of the fetus and newborn (HDFN) is caused by a mismatch between proteins in the blood of the mother and fetus. In some cases, patients require IUT in order to treat severe anemia.
The researchers hypothesized that transplacental IUT increases exposure of fetal blood antigens to the mother’s immune system. In response, the mother produces more alloantibodies, which contribute to the breakdown of fetal red blood cells.
The study included 28 pregnant individuals with red blood cell alloimmunization who received IUT at a single center.
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The authors found that 70% of those with anterior placenta experienced an increase in antibody titer after IUT, compared with 29% of those with posterior placenta. Anterior and posterior placenta are both normal variations that describe where the placenta attaches to the uterus. While anterior placenta attaches to the front of the uterine wall, posterior placenta attaches to the back.
Cases with confirmed transplacental entry had a slightly higher antibody titer than those without. This difference was not statistically significant. However, the authors caution that this could be a result of the relatively small sample size.
The researchers also calculated number needed to harm, which is a metric representing the number of individuals who must receive a treatment in order for one additional patient to experience an adverse event. This value was 2.5 among those with anterior placenta and 3.6 among those with posterior placenta.
The results of this study are hypothesis-generating, meaning this association must be investigated further to establish a causal link.
“These findings inform IUT counseling and support the need for a larger prospective study,” the authors concluded. “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 [proportion of red blood cells in the blood] secondary to enhanced alloimmunization.”
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