Effectiveness of antenatal intravenous immunoglobulin treatment in recurrent fetal and neonatal alloimmune thrombocytopenia.

objectiveTo evaluate the effectiveness of antenatal intravenous immunoglobulin (IVIG) treatment for recurrent fetal and neonatal alloimmune thrombocytopenia (FNAIT) and to determine factors associated with a good response to treatment.

methodsThis was a retrospective cohort study of pregnant women diagnosed with FNAIT and managed at a single tertiary referral center between 1992 and 2024. Affected pregnancies were treated non-invasively with weekly IVIG (1 g/kg maternal body weight) from 18-24 weeks until delivery, without platelet count monitoring. All cases were monitored with serial ultrasound for intracranial hemorrhage (ICH). Fetal blood sampling was offered at 37 weeks' gestation to determine the mode of delivery; vaginal delivery was allowed when the fetal platelet count was ≥ 50 000/μL. A good response to treatment was defined by the absence of ICH and a platelet count ≥ 50 000/μL at birth. Neonatal and maternal outcomes were assessed, and clinical characteristics were compared between pregnancies with a good response to treatment vs non-responders.

resultDuring the study period, 91 women (225 pregnancies) were diagnosed with FNAIT. Of these, 121 (53.8%) pregnancies were treated with IVIG: 48 patients had one IVIG-treated pregnancy, 17 had two, six had three, four had four and one patient had five consecutive IVIG-treated pregnancies. Only two women were treated during their first affected pregnancy based on family history; the remaining 89 women were diagnosed after the delivery of an affected neonate. IVIG treatment was declined in 15/134 (11.2%) subsequent pregnancies. Among the IVIG-treated pregnancies, 100/121 (82.6%) exhibited a good response to IVIG, with a median platelet count at birth of 172 000/μL, while 21/121 (17.4%) did not respond to treatment, with a median platelet count at birth of 27 000/μL. None of the treated pregnancies was complicated by ICH. Human platelet antigen (HPA)-1a alloimmunization was significantly more common in the group of non-responders (95.2% vs 60.0%, P < 0.01), while HPA-5 alloimmunization was significantly more common among those who responded to treatment (29.0% vs 4.8%, P = 0.02). A comparison of consecutive IVIG-treated pregnancies (totaling 115 pregnancies) revealed no significant differences between the first, second and third pregnancy with respect to platelet count at birth. However, among 11 women with at least three IVIG-treated pregnancies, four exhibited variable responses to treatment, with some pregnancies resulting in severe thrombocytopenia (platelet count < 50 000/μL) despite a good response in the preceding pregnancy. Five (5.5%) patients experienced ICH, all during their first untreated pregnancy. In subsequent pregnancies, no case of ICH was reported in either treated or untreated pregnancies.

conclusionA good response to IVIG in one FNAIT-affected pregnancy does not guarantee successful treatment in subsequent pregnancies. The reason why IVIG may be effective in one pregnancy but ineffective in a later pregnancy for the same patient remains unclear. © 2025 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.