Antenatal management of fetomaternal alloimmune thrombocytopenia--report of 15 affected pregnancies

Preparation and storage characteristics of white cell-reduced high-concentration platelet concentrates collected by anapheresis system for transfusions in utero

BACKGROUND

Important concerns with regard to in utero platelet transfusions are avoidance of volume overload and the immunomodulatory effects of residual white cells (WBCs). This study evaluated a modification of a leukocyte-reduction system (LRS, Spectra, COBE BCT) for apheresis, which collects high-concentration WBC-reduced platelets (HCPs) for in utero transfusion.

STUDY DESIGN AND METHODS

The LRS procedure was modified by running the platelet collection pump at specified low flow rates (Q(col)) for the first part of the procedure, collecting HCPs by gently purging them from the LRS chamber into a designated collection bag and then restoring the original LRS procedure settings to collect a second standard apheresis platelet concentrate (PC). Two centers carried out 32 procedures. Platelet yield, residual WBCs, and in vitro platelet function studies were evaluated.

RESULTS

Platelet concentrations in 60 mL of HCPs were predictable according to Q(col) (r(2) = 0.735). HCP yields varied from 0.9 to 3.2 x 10(11), depending on the desired final platelet concentrations in 60 mL, with an overall average of 1. 92 x 10(11) (n = 32). Apheresis PCs had a mean platelet yield of 2.9 x 10(11) (1.3-4.4 x 10(11), n = 20) and 3.9 x 10(11) (2.2-5.8 x 10(11), n = 12) at concentrations of 1.3 x 10(12) per L for single-needle and dual- needle procedures, respectively. Median WBC counts were 5.6 x 10(3) for HCPs and 2.0 x 10(4) for apheresis PCs, with >99 percent expected to be less than 1 x 10(6). HCP in vitro characteristics were equivalent to those of apheresis PCs at 24 hours after collection. In vitro performance declined over storage as a function of HCP yield. HCP pH at 22(o)C was maintained at a level of >6.2 for more than 3 days for yields >1.6 x 10(11), less than 2 days for yields 1.6 to 2.2 x 10(11), and less than 24 hours for yields >2.2 x 10(11). HCPs showed good in vitro characteristics and could be stored for 1 to 3 days, depending on the total number of platelets collected.

CONCLUSION

A standard apheresis PC and an HCP requiring no secondary processing can be collected with the Spectra LRS. The platelet concentration may be determined by clinical need. HCPs meet the requirements for components that are transfused in utero.

Prenatal treatment of severe fetomaternal alloimmune thrombocytopenia

Prenatal treatment of fetomaternal alloimmune thrombocytopenia (FMAIT) in previously affected families is of great clinical importance. We report here our experience in the prenatal treatment of 15 severely thrombocytopenic fetuses. Thrombocytopenia was in 13 cases due to immunization to HPA-1a, in one case to HPA-5b, and in one case to HPA-6b. Thirteen fetuses received altogether 34 intrauterine platelet transfusions, seven of them in combination with maternal-administered intravenous gammaglobulin (IVIG) and two in combination with IVIG and prednisone. Six of the 13 fetuses had only one transfusion just prior to delivery. In our experience, IVIG seemed to be less effective than reported; only two fetuses of eight treated initially with weekly maternal-administered IVIG responded, and these were the mildest affected cases in the study. On the other hand, owing to the short survival time, weekly platelet transfusions could only partly maintain a safe platelet count in the four fetuses treated with serial intrauterine platelet transfusions. The number of transfusions needed to be limited because of the high cumulative risk associated with repeated procedures. Three of 34 intrauterine platelet transfusions were associated with near-loss of three different fetuses due to prolonged fetal bradycardia after the transfusion. In conclusion, overall neonatal outcome was good, with no mortality; among the study group there was no intracranial haemorrhage (evaluated by postnatal ultrasonography) compared with one case in their untreated siblings. However, the problem of the optimal treatment of FMAIT remains to be solved. For the moment, the treatment of choice is a combination of maternal IVIG and platelet transfusions in severely affected cases. Serial fetal blood samplings (FBS) are needed in order to monitor the fetus with sufficient care.

Use of HLA- and HPA--matched platelets in alloimmunized patients

Refractoriness for platelet transfusion is mostly due to clinical factors but may also be caused by alloimmunization. Use of leukocyte-depleted blood cells for transfusions of patients with hematological diseases has reduced if not eliminated HLA-alloimmunization. HLA-antibodies reduce the survival time of incompatible platelets complicating seriously the platelet transfusion support in at least 5% of patients. If consecutive transfusions of HLA matched platelets also fail without identifiable clinical causes, HPA-alloimmunization may have occurred. Platelets from donors phenotyped for both HLA and HPA may produce good platelet count increments and allow optimal treatment of the basic disease despite broad spectrum alloimmunization. Additional cross-matching of phenotyped platelets with patient serum may be needed to circumvent platelet-specific antibodies of unknown specificity.

Clinical aspects and typing of platelet alloantigens

Platelet alloantigens can induce the formation of corresponding alloantibodies when exposed to phenotypically negative individuals. These antibodies are responsible for fetal and neonatal alloimmune thrombocytopenia, posttransfusion purpura, passive alloimmune thrombocytopenia and transplantation-associated thrombocytopenia and may contribute to platelet transfusion refractoriness together with HLA antibodies. Besides antibody detection laboratory diagnosis of the clinical syndromes requires alloantigen typing. Furthermore, typed platelet donors are a prerequisite for effective platelet transfusion therapy. Different techniques for phenotyping are well established and easy to perform but they rely on the availability of antisera. Since the molecular genetic background of the clinically most relevant alloantigens has been elucidated during the last years various genotyping methods have been applied to the platelet membrane polymorphisms and thus facilitated widespread platelet alloantigen typing. Generation of antibodies from phage display libraries and of lymphoblastoid cell lines from donors with all genetic variants will allow further developments.

The fetal and neonatal consequences of maternal alloimmune thrombocytopenia

Alloimmune thrombocytopenia is a relatively common and under-recognized entity. Prospective screening studies have suggested that at least 1 in every 1000 babies will be affected. While the severity of prospectively identified neonates is not as great as those 'routinely' identified as newborns, the incidence of intracranial haemorrhage in the fetus and neonate is the highest for any immune thrombocytopenia. Diagnosis is complex for the laboratory in view of the large number of platelet antigens and the importance of having sufficient numbers of typed controls. The importance of identifying the affected newborn extends to the likely need for antenatal management of the subsequent affected fetus. Studies to determine the optimal approach to this problem are ongoing. Ideally, prenatal screening of all pregnant women could be performed but this is not currently in practice.

Feto-maternal alloimmune thrombocytopenia: antenatal therapy with IvIgG and steroids--more questions than answers. European Working Group on FMAIT

The optimal antenatal therapy for fetal thrombocytopenia has not been determined. We analysed 37 cases managed by maternal therapy and observed a successful outcome of maternal treatment in 26% of IvIgG cases and in 10% of steroid-treated cases. The significance of a plateau of the fetal platelet counts during pregnancy, 41% of IvIgG cases and 20%, of cases treated with steroids, is uncertain. It may indicate a stabilization of thrombocytopenia, hence a beneficial effect of therapy, or the natural course of the platelet count in a low-risk pregnancy. Overall outcome was unpredictable, but amongst the therapy failures there were proportionally more severely affected siblings. Further multicentre studies are necessary to establish the optimal antenatal management of high-risk pregnancies.

Immune thrombocytopenia in pregnancy: autoimmune and alloimmune

Auto- and alloimmune thrombocytopenias in pregnancy may seriously impact on both mother and fetus. Autoimmune thrombocytopenia (ITP) affects both mothers and fetuses but is considered to be quite benign for both groups. The 'facts' are that: 1) ITP occurs commonly in pregnancy; 2) there has been no reported maternal mortality in more than 20 years; 3) management, except at delivery, is similar to management in the non-pregnant state; 4) splenectomy is virtually never required during pregnancy; 5) significant neonatal thrombocytopenia occurs in approximately 10% of cases and intra-cranial hemorrhage (ICH) 1%; 6) the course of the first sibling predicts that of the next sibling; and 7) the fetal platelet count can be successfully determined (if desired) by either fetal blood sampling (FBS) or by fetal scalp sampling. Many other important considerations remain undetermined: 1) non-invasive prediction of severe fetal thrombocytopenia; 2) the appropriate mode of delivery for a thrombocytopenic fetus; 3) the role of anti-platelet antibody testing; and 4) the effects on the fetal platelet count of maternal therapy. Alloimmune thrombocytopenia (AIT) is easier to outline because it is a far more serious fetal disorder: 1) neonatal platelet counts < 20,000/microliter are common in AIT; 2) there is a 10-30% ICH rate in first affected newborns, some of which occur antenatally; 3) there is no universal prenatal screening although this would be scientifically feasible; 4) testing is complex and requires an experienced laboratory that can test at least five platelet antigens and has sufficient typed controls to confirm the specificity of any anti-platelet antibodies detected; 5) the second affected sibling in a family is usually more severely affected than the first; 6) treatment of the thrombocytopenic neonate can be accomplished with intravenous (i.v.) gammaglobulin and/or platelet transfusions; and 7) treatment of the fetal platelet count can be accomplished in most instances by infusing the mother with i.v. gammaglobulin with or without steroids; platelet transfusions to the fetus is another option.

Fetal alloimmune thrombocytopenia

BACKGROUND

Alloimmune thrombocytopenia is a serious fetal disorder resulting from platelet-antigen incompatibility between the mother and fetus. The diagnosis is usually made after the discovery of unexpected neonatal thrombocytopenia. Approximately 10 to 20 percent of affected fetuses have intracranial hemorrhages, one quarter to one half of which occur in utero. We studied the correlates of thrombocytopenia in affected fetuses.

METHODS

We studied 107 fetuses with alloimmune thrombocytopenia at a mean (+/-SD) gestational age of 25+/-4 weeks, before their entry into one of three treatment protocols. The fetuses were initially evaluated because an older sibling had been given this diagnosis at birth. We compared the initial platelet counts in utero in these 107 fetuses with the platelet count at birth and the history of intracranial hemorrhage in the affected sibling.

RESULTS

The initial platelet count was < or =20,000 per cubic millimeter in 53 of the 107 fetuses (50 percent), including 21 of 46 fetuses (46 percent) studied before 24 weeks of gestation. The 97 fetuses with PI(A1) incompatibility had more severe thrombocytopenia than the 10 fetuses with other antigen incompatibilities. Among seven fetuses with platelet counts of more than 80,000 per cubic millimeter that were not treated initially, the counts decreased by more than 10,000 per cubic millimeter per week. Although 41 fetuses had initial platelet counts that were lower than those measured at birth in an older affected sibling, only a history of antenatal intracranial hemorrhage in the sibling predicted greater severity of thrombocytopenia in the fetus. Only one treated fetus had an intracranial hemorrhage, and the thrombocytopenia resolved after birth in all cases.

CONCLUSIONS

Fetal alloimmune thrombocytopenia occurs early in gestation, is severe, and is more severe in fetuses with an older affected sibling who had had an antenatal intracranial hemorrhage.

[Neonatal alloimmune thrombopenia in anti-HPA-3a (Baka) immunization]

BACKGROUND

Neonatal alloimmune thrombocytopenia (NAIT) in the HPA-3a system is responsible for less than 5% of all cases of NAIT.

CASE REPORT

Thomas, a male infant, was born at 39 weeks of gestation after an uncomplicated pregnancy. Delivery was normal. The Apgar score was 9 at 1 minute, and 10 at 5 and 10 minutes. At 1 hour of age, he displayed extensive petechiae and purpura over the back. The platelet count was 8,000/mm3. Hematesis and extensive petechiae were noted, leading to an exchange transfusion followed by a transfusion of 0.5 U/kg of random donor platelets, 0.4 g/kg/d of intravenous immunoglobulin (IVIg) and 10 mg/kg/d of corticosteroids. IVIg were discontinued on d5 and corticosteroids on d10. There was no relapse of thrombocytopenia. A neonatal alloimmune thrombocytopenia with an HPA-3a (Baka) incompatibility was confirmed.

CONCLUSION

HPA-3a incompatibility is certainly more frequent than the rare cases reported and must be searched for in all cases of neonatal thrombocytopenia.

Severe fetomaternal alloimmune thrombocytopenia presenting with fetal hydrocephalus

We report two patients where the finding of isolated fetal hydrocephalus led to the detection of severe fetal thrombocytopenia, using fetal blood sampling. Serological investigation led to the diagnosis of fetomaternal alloimmune thrombocytopenia (FMAIT) due to anti-HPA-1a. Both women had had previous unsuccessful pregnancies probably due to FMAIT; one had had four miscarriages at 17-18 weeks' gestation. The other had had one previous pregnancy complicated by severe fetal anaemia, and eventually hydrocephalus developed and the fetus died without the diagnosis of FMAIT being considered. Subsequent pregnancies in the two women were also affected by FMAIT, but prenatal treatment, predominantly with serial fetal platelet transfusions, resulted in a successful outcome in both cases. These observations suggest that FMAIT should be suspected if there is isolated fetal hydrocephalus, unexplained fetal anaemia, or recurrent miscarriages. The accurate diagnosis of FMAIT is important because recent advances in prenatal management can improve the outcome of subsequently affected pregnancies.

Fetal transfusion therapy

Rapid advances are occurring in the diagnosis and treatment of the fetus with a red blood cell or platelet cytopenia. Noninvasive methods of monitoring the alloimmunized pregnancy, invasive methods such as amniocentesis and cordocentesis, and intrauterine transfusion therapy of both red cells and platelets, are being further refined to allow the prompt recognition and treatment of fetal cytopenias. Specialized centers have now accrued a large experience in the management of the fetus severely affected by alloimmunization. Advances in ultrasound, blood banking techniques, and genetic engineering technology have spurred the most recent advances. The indications for diagnosis, timing and frequency of invasive procedures for treatment, and technical considerations regarding preparation of blood products and volume of transfusion, are outlined in this review. Polymerase chain reaction (PCR) determination of fetal Rh(D) genotype by chorionic villus sampling or amniocentesis in the first or second trimesters is a recent clinically useful advance. The advent of hematopoietic stem cell transplantation and the potential for gene therapy are exciting advances in the treatment and prevention of hematopoietic diseases, including, but not limited, to the fetal cytopenias.

The prenatal identification of fetal compatibility in neonatal alloimmune thrombocytopenia using amniotic fluid and variable number of tandem repeat (VNTR) analysis

Most severe episodes of neonatal alloimmune thrombocytopenic purpura (NATP) are caused by antiplatelet alloantibodies against the HPA-1a (PlA1) antigen. However, half of subsequent fetuses produced from a HPA-1a/b father (genotypic frequency 28%) will result in a child who is not affected. Some investigators manage NATP by confirming the fetal platelet phenotype using percutaneous umbilical cord sampling, a procedure that carries a low but real risk of fetal morbidity and mortality. More recently, physicians determine the fetal platelet antigen genotype using DNA derived from amniotic fluid or chorionic villus samples. All therapy is withdrawn for a fetus who genotypes as HPA-1b/b. However, since the fetus is the same genotype as the mother, there can be uncertainty about the origin of the genetic material and thus the validity of the fetal genotype. The inappropriate withdrawal of therapy for a erroneously genotyped fetus could be fatal, and consequently many physicians advocate fetal HPA-1 phenotyping with confirmation using percutaneous umbilical blood sampling. In this report we describe the management of two pregnancies with previously affected infants due to anti-HPA-1a alloantibodies. Both husbands were HPA-1a/b. For the current pregnancies, amniotic fluid was collected at 20 or 29 weeks of gestation, and the platelet genotype indicated that the fetuses were HPA-1b/b. The fetal origin of the amniotic fluid derived DNA was confirmed by the forensic technique of DNA profiling using variable number of tandem repeat (VNTR) analysis. All therapy was withdrawn, percutaneous umbilical blood sampling was not performed, and both women vaginally delivered healthy non-thrombocytopenic infants. The application of platelet alloantigen genotyping using DNA from amniotic fluid cells identified the HPA-1b/b fetus, and VNTR analysis confirmed that the tissue was fetal derived, thus avoiding the necessity for percutaneous umbilical blood sampling. The use of this approach in patients at risk will avoid additional investigation and treatment in approximately one-seventh of all NATP pregnancies involving the HPA-1a antigen.

Antenatal screening for fetal alloimmune thrombocytopenia: the results of a pilot study

Feto-maternal incompatibility for the human platelet antigen HPA-1a is an important cause of severe fetal thrombocytopenia. The incidence is 1 in 1000-2000 pregnancies, which is more common than other conditions for which screening is presently carried out. Antenatal diagnosis and management are now available, but only for subsequent siblings following diagnosis of a previously affected infant. This study describes a pilot prospective screening programme for the antenatal detection of fetomaternal alloimmune thrombocytopenia (FMAIT) due to HPA-1a incompatibility. 3473 women were typed for HPA-1a using a method designed for large-scale typing. 71 women found to be HPA-1a negative were further tested for HLA-DR52a as a risk factor for alloimmunization. All women were monitored for the development of anti-HPA-1a throughout pregnancy and a cord full blood count was taken at delivery. Two affected pregnancies were found and treated: a singleton pregnancy was treated antenatally and a twin pregnancy after delivery. The study showed that screening for FMAIT could be established within the pre-existing antenatal red cell serology programme. It was concluded that screening should be based on platelet typing and offered regardless of parity. Further stratification, combining DR52a typing and HPA-1a antibody screening, although focusing on the group of women at greater risk, may not identify all affected pregnancies. Confirmation of the diagnosis and severity of FMAIT continues to depend on fetal blood sampling during pregnancy or cord blood samples after birth.