Neurodevelopmental Outcome After Fetal Neonatal AlloImmune Thrombocytopenia

INTRODUCTION AND RATIONALE Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is the most common cause of thrombocytopenia in otherwise healthy term-born neonates. FNAIT is a rare disease with an incidence estimated around 1 per 1000 live newborns. During pregnancy alloimmunization can occur due to incompatibility of the Human Platelet Antigens (HPA) on the maternal and fetal platelets. Alloimmunization and maternal production of antibodies directed against the HPA-positive fetal platelets, leads to thrombocytopenia and an increased risk of intracranial hemorrhages (ICH) in the fetus. Clinical presentation can vary from skin bleedings to severe ICH leading to lifelong neurologic sequelae or intrauterine death.

In the past, FNAIT was managed with invasive and high-risk interventions including intrauterine platelet transfusion (IUPT). Since the end of the 20th century, invasive intrauterine transfusions (IUT) were replaced by a new, non-invasive therapy: maternal administration of intravenous immunoglobulin (IVIg). This novel therapy resulted in a significant lower risk of intrauterine fetal death and ICH. Intervention with immune modulation in the semi -allogenic environment of the fetus by administration of immunoglobulins (Ig) is successful, especially in preventing ICH. However antenatal treatment with IVIg has been implemented as standard of care without strong methodological follow-up research of children from mothers treated with IVIg. To date, only two follow-up studies have been published in children with anticipated FNAIT cases. The first study of a FNAIT cohort treated with IVIg was done by Ward et al. in 2006. They concluded that development of children treated for FNAIT was better compared to their non-treated siblings. Their conclusions were based on non-validated questionnaires taken by telephone, assessing the behavioral outcome of the children and were limited by a ~40% lost-to-follow-up rate. A second follow-up study including 39 children was published by a research group from our center in 2004. This research stated that the outcome in children with FNAIT and exposed to maternal IVIg treatment was similar to the normal population. However, this study included a heterogenic group of children with different treatment strategies including IUT, hampering definitive conclusions and substantiating the need for more research.

No long-term standardized follow-up studies were performed on FNAIT cases without antenatal treatment and/or ICH. The natural course of the disease and long-term effects of thrombocytopenia on the developing fetus and newborn are unknown. FNAIT is defined as a disease caused by alloantibodies, resulting in thrombocytopenia and a risk of bleeding in the neonate. In the last years, evidence is increasing that the maternal alloantibodies can also bind to the fetal endothelium and may impair angiogenesis in the developing fetuses It is not known at which moment in pregnancy the developing brain is most vulnerable for damage induced by these kind of alloantibodies. The timing in fetal life FNAIT associated ICH ranges from 23 to 42 weeks, but small bleeding may not be diagnosed. It may also be that these type of alloantibodies not lead to ICH but to other type of cerebral damage. These lesions can remain subclinical directly after birth but lead to developmental delay on the long term. This knowledge can be of great interest when counseling parents with a risk of FNAIT or in writing guidelines.

For 3 decades a nationwide screening on FNAIT to detect pregnancies with alloantibodies in time and start treatment to prevent bleedings is being discussed. If alloantibodies lead to cerebral damage on the long term also in patients without large ICH this might have large implications in the debate on the introduction of a national screening programme. Therefore the investigators want to underline that more knowledge about the long-term development of FNAIT survivors is required.

The Leiden University Medical Center (LUMC), a national fetal therapy center in The Netherlands, has a close and long-lasting collaboration with Sanquin. This collaboration offers a unique opportunity to evaluate a large and complete cohort of children with FNAIT. LUMC and Sanquin are both nationwide referral centers for FNAIT and committed to improve timely detection of high-risk cases who need intra-uterine therapy. This research group from the national expertise centers are designated to assess long-term outcome in children with FNAIT and describe the natural history of children affected by FNAIT and the long term effects of a given therapy.