Neonatal alloimmune thrombocytopenia due to a new platelet-specific alloantibody

An infant with severe neonatal alloimmune thrombocytopenia is described in whom an antibody directed at a new platelet-specific alloantigen, Ca (HPA-6b), is implicated. The new alloantigen is of low frequency in the population and was localized to platelet glycoprotein (GP) IIIa. Immunoprecipitation studies using murine monoclonal antibodies specific for the GP complex IIb-IIIa and GPIIIa alone (AP2 and AP3) suggest that the location of the Ca epitope on GPIIIa may be near the binding site for AP3. Neonatal alloimmune thrombocytopenia associated with Ca is likely to be as severe as that seen in cases due to incompatibilities for the HPA-1 (PIA) and HPA-4 (Pen) platelet alloantigen systems, because each is located on GPIIIa, a densely represented molecule on the platelet surface.     

Neonatal alloimmune thrombocytopenia

Neonatal alloimmune thrombocytopenia (NAIT) occurs when maternal alloantibodies to antigens present on fetal platelets cause their immune destruction resulting in thrombocytopenia in the newborn infant or fetus. Bleeding may be severe; intracranial haemorrhage and permanent neurological damage are the most serious complications. Despite the severity of the disease, there is often a delay in making the correct diagnosis and instigating appropriate treatment. Recent evidence that NAIT is more common than has previously been recognised, a better understanding of the molecular basis of platelet serology and advances in technology, which have made it possible to take blood samples from fetuses and transfuse them in utero, have all contributed to a growing interest in this condition. In addition, it is exciting to realise that an aggressive approach to the management of established cases and 'at risk' pregnancies can prevent serious neurological sequelae and dramatically improve the outcome for affected infants.     

Neonatal alloimmune thrombocytopenia: spontaneous in utero intracranial hemorrhage

Neonatal alloimmune thrombocytopenia is an uncommon but important cause of thrombocytopenia in infants. Because of the severity of the thrombocytopenia, some of these infants will have intracranial hemorrhage with resultant long-term disability. Obstetricians and neonatologists have recommended delivery by caesarean section and the rapid institution of appropriate treatment for the infant; however, it is theoretically possible that a hemorrhagic event could precede the delivery and consequently not be prevented by these perinatal interventions. In this report we describe a neonate in whom the diagnosis of alloimmune neonatal thrombocytopenia was suspected because of antenatal ultrasound evidence of intracerebral hemorrhage. This case demonstrates the importance of antenatal fetal assessment and indicates the need for the development of therapeutic strategies to maintain fetal hemostasis.     

Neonatal outcome in alloimmune thrombocytopenia after maternal treatment with intravenous immunoglobulin

Background

Weekly maternal intravenous immunoglobulin (IVIG) is the cornerstone of antenatal treatment of foetal and neonatal alloimmune thrombocytopenia (FNAIT). The aim of this study was to describe the neonatal outcome and management in neonates with FNAIT treated antenatally with IVIG.

Materials and methods

All neonates treated antenatally and delivered at our centre between 2006 and 2012 were included in the study. We assessed the neonatal outcome and management, including the occurrence of intracranial haemorrhage, platelet count at birth and need for postnatal platelet transfusions or postnatal IVIG treatment.

Results

A total of 22 neonates were included of whom 12 (55%) had severe thrombocytopenia at birth (platelet count ≤50×10⁹/L). Most neonates (67%, 8/12) with severe thrombocytopenia received a platelet transfusion after birth. None of the neonates required postnatal treatment with IVIG. Three neonates had petechiae and haematomas, without clinical consequences. One foetus suffered from intracranial haemorrhage, which was detected just before the planned start of antenatal IVIG at 28 weeks’ gestation.

Discussion

Our results suggest that antenatal maternal IVIG and, if necessary, postnatal matched platelet transfusions, are effective and safe for the treatment of FNAIT.     

The management of alloimmune neonatal thrombocytopenia.

Neonatal alloimmune thrombocytopenia (NAITP), defined as thrombocytopenia (platelet count < 150 x 10(9)/l) due to transplacentally acquired maternal platelet alloantibodies, occurs in approximately 1 per 1200 live births in a Caucasian population. In such a population, the majority (> 75 percent) of cases are due to fetomaternal incompatibility for the platelet specific alloantigen, HPA-1a (P1A1, Zwa). Incompatibility for the HPA-5b (Bra) alloantigen is the next most frequent cause of NAITP in Caucasians; much less common is NAITP due to incompatibility for HLA, blood group ABO or other platelet-specific antigens. In non-Caucasian populations (e.g. Orientals) HPA-1a incompatibility is a rare cause of NAITP and other alloantigens e.g. HPA-4b (Penb, Yuka) are implicated. The greatest clinical challenge relates to the antenatal management of pregnant women alloimmunized to the HPA-1a (P1A1, Zwa) antigen, and particularly the subset of such women who have a history of a previously affected infant with severe thrombocytopenia and/or intracranial hemorrhage (ICH). The risk of antenatal ICH in the fetus of such women is high enough to merit intervention, either weekly infusion of high-dose intravenous immunoglobulin G (IVIG) with or without corticosteroids given to the mother (the preferred approach in North American centres), or repeated in-utero fetal platelet transfusions (the preferred treatment approach in some European centres). Post-natal management of severely affected infants centres on the rapid provision of compatible antigen-negative platelets harvested from the mother or a phenotyped donor. The value of antenatal screening programs to detect 'at risk' alloimmunized women during pregnancy continues to be debated.     

Anti-HPA-5b-induced neonatal alloimmune thrombocytopenia: antibody titre as a predictor. Collaborative Study Group

Anti-HPA-5b is the most commonly found platelet-specific antibody among pregnant women, but it does not cause severe fetal-neonatal alloimmune thrombocytopenia in the majority of affected infants. However, as the sequelae of the affected children may become severe, it is necessary to identify the risk factors for neonatal alloimmune thrombocytopenia. Of 21 354 consecutive pregnant women, 138 [0.65%; 95% confidence interval (CI) 0.54-0.75%], corresponding to 13.2% of the 1049 HPA-5b- women calculated by the gene frequency, were positive for anti-HPA-5b at the first trimester. Anti-HPA-5b was titrated in specimens obtained at the third trimester and antibody-positive women and their neonates were HPA-5 genotyped. Platelet counts in cord blood and 3 d after birth were assessed in the infants born to these mothers. Chi-square analysis showed no significant relationship between the titres of maternal antibody to HPA-5b and the number of pregnancies. There was a significant difference in platelet counts at d 3 between neonates who were compatible (267 x 109/l) or incompatible (220 x 109/l, P < 0.05) with maternal anti-HPA-5b. HPA-5b antibody titres >/= 64 were related to the development of thrombocytopenia (< 150 x 109/l) in neonates 1 d and 3 d after birth. A high titre (>/= 64) had a positive predictive value of 50% for thrombocytopenia 3 d after birth when the infant was HPA-5b+ and a negative predictive value of 100%. These results indicate that a high titre (>/= 64) of anti-HPA-5b is associated with a higher risk of neonatal thrombocytopenia, even if anti-HPA-5b-induced severe thrombocytopenia rarely develops.     

HLA antibodies and neonatal alloimmune thrombocytopenia

A female baby with a severe thrombocytopenia at 18 x 10(9)/l was born to a 29-year-old (gestation 2/partum 2) mother. Scattered petechiae were present on her legs, arms, chest and face, but there was no bleeding, infection, fever or hepatosplenomegaly. A platelet antibody screening immunocapture test was positive, which was performed on the mother's serum 3, 12 and 38 days after delivery, but no platelet-specific antibodies were found by the monoclonal-antibody-specific immobilization of platelet antigen assay. The baby's platelets and lymphocytes and the father's platelets reacted strongly with the HLA antibodies present in the mother's serum. The neonate was treated with intravenous human immunoglobulin (Tegeline), 1 g/kg per day) 1, 2 and 3 days after delivery. The platelet count rose from 18 x 10(9)/l on day 0 to 37 x 10(9)/l on day 3 and to 227 x 10(9)/l on day 12. No platelet transfusion was needed. Several factors which developed hereafter lead us to think that this neonatal alloimmune thrombocytopenia is due to the transplacental passage of maternal HLA antibodies to the baby.     

Neonatal thrombocytopenia

Neonatal thrombocytopenia is a common clinical problem. The majority of episodes are early-onset thrombocytopenias due to impaired fetal megakaryocytopoiesis associated with placental insufficiency; the commonest causes of severe early-onset thrombocytopenia are immune thrombocytopenias, congenital infections, and asphyxia. By contrast, about 90% of cases of severe thrombocytopenia presenting after the first few days of life are due to late-onset bacterial sepsis, necrotizing enterocolitis, or both. Although clinically stable neonates tolerate relatively low platelet counts without significant risk of hemorrhage, ill or clinically unstable neonates with profound thrombocytopenia often have a poor outcome. Currently, the only therapy is platelet transfusion. Despite many published guidelines for platelet transfusion in the newborn, however, there have been no randomized trials to define the safe lower limit for platelet counts in sick neonates. The platelet threshold at which the benefits of transfusion outweigh the risks in neonates remains unclear. Well-designed trials are urgently needed.     

High-dose IgG treatment for neonatal alloimmune thrombocytopenia

Summary Twelve children with neonatal alloimmune thrombocytopenia (NAT) due to Zw^a incompatibility were treated with intravenous IgG (IVIG). Total doses ranged between 1 and 9 g. Ten out of 12 infants had a favorable response. It is concluded that IVIG can serve as an emergency treatment in NAT if material (or compatible) platelets are not available.This work was supported by the Deutsche Forschungsgemeinschaft (Mu 277/9–6)Presented at the International Workshop on ITP, August 26 and 27, 1988, Lucerne, Switzerland