Neonatal thrombocytopenia due to passive immunization: prenatal diagnosis and distinction between maternal platelet alloantibodies and autoantibodies

Immune thrombocytopenia in pregnancy

Autoimmune thrombocytopenia (ITP)

1) The risks to mother and fetus have previously been overstated.

2) There is no maternal test which will accurately determine fetal thrombocytopenia.

3) The only reliable test for fetal thrombocytopenia is cordocentesis – this carries a higher morbidity than that of fetal intracerebral haemorrhage from ITP.

4) Contrary to received wisdom, there is no evidence that, even for the most severely thrombocytopenic infant, abdominal delivery protects against intracranial haemorrhage.

5) Management therefore involves keeping the maternal platelet count above 50 × 1091 and choosing the route of delivery on normal obstetric grounds.

Alloimmune thrombocytopenia

1) Alloimmune thrombocytopenia is commoner than hitherto believed (0.15% all neonates).

2) The fetal risks are considerable: intracranial haemorrhage occurs in 4% of cases antenatally and in 10% in labour. The risks are virtually confined to those with a platelet count of less than 30 × 109l−1.

3) Cordocentesis is justified for the ‘at risk’ fetus; fetal immunoglobulin or platelet therapy can be given.

4) When the fetal platelet count is below 50 × 109l−1, abdominal delivery should be planned.

5) A maternal screening test for neonatal alloimmune thrombocytopenia exists (lack of P1A1 antigen).

Serologic analysis of three cases of neonatal alloimmune thrombocytopenia associated with HLA antibodies

BACKGROUND

Neonatal alloimmune thrombocytopenia (NAIT) is caused when maternal alloantibodies react with paternally inherited antigens present on the fetal PLTs, a reaction mainly due to antibodies against human PLT antigens. Cases in which NAIT has been caused by HLA antibodies are relatively rare. In this study, three cases of NAIT associated with HLA antibodies that occurred in a 1-year period are reported.

STUDY DESIGN AND METHODS

The presence of HLA antibodies in these three NAIT case studies was elucidated by examining reactions of the neonatal and maternal sera with lymphocytes, PLTs, and beads from an HLA antibody screening test (FlowPRA, One Lambda Inc.). Absorption and elution tests with paternal cells were also conducted. In addition, the influence of titer and specificity of HLA antibodies on NAIT was analyzed in light of 24 other documented cases in Japan.

RESULTS

In the three case studies presented herein, antibodies against human PLT antigens were found in neither the maternal nor neonatal sera, while specific HLA antibodies were identified in both sera. Absorption of maternal serum with paternal PLTs eliminated the reactivity against paternal PLTs and lymphocytes.

CONCLUSION

Transplacental passage of maternal HLA antibodies was observed in the three neonates cited in the present study.

Feto-maternal alloimmune thrombocytopenia: a literature review and statistical analysis

Exploring prognostic factors that determine outcomes in fetomaternal alloimmune thrombocytopenia (FMAIT), a search of Medline was performed covering the years 1966 to April 1998. 376 articles were collected and reviewed; 140 articles contained the case histories of 297 mothers and 433 pregnancies that fulfilled entry criteria. More than 30 data variables were sought from these cases. The data were analysed using SPSS and Arcus Quickstat Biomedical. Nineteen different antigen incompatibilities were documented, the majority being human platelet antigen (HPA)-1a (77.3%), HPA-3a (3.5%) and HPA-5b (3.5%). The relative risk reduction (RRR) in mortality with any intervention was 57% (0.19-0.77) p = 0.009. Treatment of HPA-1a (PlA1) pregnancies with intravenous immunoglobulin (IVIG) increased the likelihood of a neurologically normal outcome, relative risk (RR) 1.68, confidence interval (1.3-2.2) p = 0.0003. Treatment of HPA-1a (PlA1) pregnancies with only antenatal complementary platelet transfusions increased the likelihood of a neurologically normal outcome, RR 1.63 (1.1-2.1) p = 0.01. Despite reviews of more than 400 cases of FMAIT, few prognostic variables are identifiable. Although IVIG appears to reduce the risk of intracranial haemorrhage (ICH), the dosage and timing of IVIG treatment was varied. This study highlights the need for standardised and directed research.

Gestational thrombocytopenia and immune thrombocytopenias in pregnancy

Appropriate management of thrombocytopenia in the pregnant patient is important for the well-being of both mother and fetus. The healthy-appearing mother with mild thrombocytopenia may have either gestational benign thrombocytopenia, which does not produce fetal thrombocytopenia, or immune-mediated thrombocytopenia, which can produce fetal thrombocytopenia. These two types of pregnancy-associated thrombocytopenias can be differentiated. Gestational benign thrombocytopenia is initially discovered during pregnancy, and in these patients a reliable test for antiplatelet antibody is usually negative. Conversely, patients with immune-mediated thrombocytopenia may have a history of thrombocytopenia before the pregnancy, and these patients usually have a detectable antiplatelet antibody. The pregnancy patient who presents with a normal platelet count and a history of neonatal alloimmune thrombocytopenia in a prior pregnancy or with a history of an infant of a close relative with NAT must be carefully monitored. Antiplatelet antibody assays performed on mother's and baby's blood will help determine if an antiplatelet antibody is present in maternal plasma, if the antibody reacts with the baby's platelets, and (with appropriate typing plasma) the antigenic specificity of the maternal and fetal platelets. In addition, antigenic typing of the father's platelets will help determine the risk of NAT in the current pregnancy. If a fetus is at risk for severe immune-mediated thrombocytopenia from either an autoantibody or an alloantibody, the fetal platelet count should be measured, if possible, from blood obtained by umbilical cord puncture. If the fetal platelet count is less than 50,000/microL or cannot be measured but is thought to have a high probability of being less than 50,000/microL, strong consideration should be given to a cesarean delivery.

Perinatal diagnosis of passive ITP: use of percutaneous umbilical blood sampling (PUBS)

Fetal blood samples can be obtained in utero by direct sampling of the umbilical cord vessels, using an ultrasound guided technique termed percutaneous umbilical sampling (PUBS). This procedure is being used more frequently in high risk pregnancies to obtain direct fetal laboratory data. In specialized centers, with trained personnel, the technique can be used with a high degree of safety and efficiency. Direct access to the fetal circulation can also allow an accurate determination of the fetal platelet count in cases of suspected fetal thrombocytopenia. The technique may be used to plan appropriate clinical management of maternal ITP as well as to diagnose the presence of fetal alloimmune thrombocytopenia. A logical strategy for obstetric management and evaluation of fetal risk can be planned. The procedure also has the potential to allow direct fetal treatment as has been the case in the management of severe fetal anemia.

Platelet antibody: review of detection methods

The driving force behind development of in vitro methods for platelet antibodies is identification of plasma factors causing platelet destruction. Early methods relied on measurement of platelet activation. Current methods are more specific and use a purified antibody against immunoglobulin or complement, which is usually labeled with 125I or tagged with an enzyme or fluorescein. Comparisons of quantitation of platelet-associated IgG show wide variability between different methods. The disparate results can be related both to differences in binding of secondary antibodies to immunoglobulin in solution compared to immunoglobulins attached to platelets and to the improper assumption that the binding ratio between the secondary detecting and primary antiplatelet antibody is one. Most assays can 1) identify neonatal isoimmune thrombocytopenia and posttransfusion purpura, 2) help to differentiate between immune and nonimmune thrombocytopenias, 3) help to sort out the offending drug when drug-induced thrombocytopenia is suspected, and 4) identify platelet alloantibodies and potential platelet donors via a cross match assay for refractory patients. However, the advantages of quantitative assays over qualitative methods with respect to predictions of patients clinical course and response to different treatments remain to be investigated.

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.

The current status of antiplatelet antibodies

The importance of antiplatelet antibodies in clinical medicine was first recognized in 1951. Since that time, a number of syndromes have been described, including autoimmune thrombocytopenia purpura, posttransfusion purpura, neonatal alloimmune thrombocytopenia, and drug-induced thrombocytopenia purpura, that fit into the category of immunologic thrombocytopenias. The laboratory methods for detecting the antiplatelet antibodies present in these diseases are enumerated and discussed along with the currently recognized platelet-specific antigens. Because of the complexities of performance and the lack of agreement among many of the available procedures, it is recommended that antiplatelet antibody testing remain primarily a research tool for the present time.

Neonatal alloimmune thrombocytopenic purpura: a case report

We report a case of a sibling pair with neonatal alloimmune thrombocytopenic purpura. Serial antepartum platelet alloantibody quantitation by an enzyme-linked immunoabsorbent assay revealed rising antibody titers during advancing gestation. We discuss the implications of this finding in the antepartum diagnosis of neonatal alloimmune thrombocytopenic purpura, a rare, but frequently fatal disorder.

Autoimmune thrombocytopenic purpura: current concepts and recommended practices

Autoimmune thrombocytopenic purpura is the most common autoimmune disorder encountered in the pregnant patient. It is potentially fatal for the mother and fetus yet treatable and potentially curable. Analysis of current perinatal literature reveals not only a great deal of interest and activity in the study of this syndrome and its special problems during pregnancy but also significant controversy. The disease can be acute or chronic and vary in time of onset and severity of manifestations. If not forewarned with an awareness of this disorder's pathogenesis and potential fetal effects particularly in the pregnant woman who has undergone splenectomy, the obstetrician cannot respond appropriately. The usefulness of platelet antibody determinations to facilitate obstetric management decisions is discussed. The importance of cooperative care among the obstetrician, hematologist, and neonatologist is emphasized. Recommendations for management of autoimmune thrombocytopenic purpura in pregnancy are derived from a review of current concepts of the disorder's pathogenesis, pathophysiology, criteria for diagnosis, and modes of therapy as well as special maternal/fetal considerations of antepartum, intrapartum, and postpartum care.

The prenatal prediction of thrombocytopenia in infants of mothers with clinically diagnosed immune thrombocytopenia

The management of the pregnant patient with immune thrombocytopenia is complicated by the unavailability of the fetal platelet count. Since the transplacental passage of antiplatelet antibodies mediates infant thrombocytopenia, measurement of maternal platelet-associated IgG might predict infant outcome. We related the maternal platelet count and platelet-associated IgG level to the infant's platelet count in 41 pregnancies in 38 patients who were clinically diagnosed as having immune thrombocytopenia. Fifteen of 39 live-born infants were thrombocytopenic at delivery. Maternal platelet-associated IgG was predictive of infant platelet count but maternal platelet count was not; only one of the 20 infants delivered of the 18 thrombocytopenic mothers with normal platelet-associated IgG was affected, whereas 11 of 12 thrombocytopenic mothers with elevated platelet-associated IgG had thrombocytopenic infants. Five infants died in utero between 18 and 28 weeks' gestation, but otherwise there was no significant morbidity in the live births. Measurement of platelet associated IgG in mothers with immune thrombocytopenia during pregnancy can be used to predict infant thrombocytopenia, although it does not predict the severity of the thrombocytopenia.

Immune thrombocytopenic purpura and pregnancy

Neonatal thrombocytopenia is a potentially life-threatening complication of immune thrombocytopenic purpura (ITP). We followed 23 pregnant women who had either a history of ITP (11 women) or clinically active disease (12 women) to delineate the factors responsible for neonatal thrombocytopenia. No relation was observed between maternal and neonatal platelet counts (P greater than 0.5). Eleven women delivered thrombocytopenic children; antiplatelet antibodies were detectable in each mother, including five who were in clinical remission at delivery. The level of platelet-associated IgG in the mothers did not identify the neonates at risk for thrombocytopenia (P greater than 0.05). However, the level of maternal circulating antiplatelet antibody correlated with both the presence and the extent of neonatal thrombocytopenia (P less than 0.005). A discrepancy between maternal platelet count and maternal antibody level may be especially notable in mothers treated with steroids or splenectomy. Monitoring the level of circulating antiplatelet antibody may help in identifying and managing pregnant women with ITP at risk of delivering neonates with serious thrombocytopenia.

The obstetrical management of patients with immunologic thrombocytopenic purpura

Pregnant women with immunologic thrombocytopenic purpura (ITP) run the risk of complications during pregnancy and labor, mainly due to the possibility of hemorrhage. Antibodies pass through the placenta, causing a transient, but dangerous thrombocytopenia in the fetus and infant. Four women with ITP, having five deliveries, are presented, showing that the modern treatment of these patients includes corticosteroids during pregnancy, thrombocyte transfusion during labor, and splenectomy being or after the pregnancy in selected cases. Cesarean section is not indicated for the disease per se, and fetal scalp blood sampling for thrombocyte count during labor is not necessary. The newborn needs immediate, careful control and, if necessary, thrombocyte transfusion and even steroids. Prolonged follow-up of the infants is necessary.