Very early intracranial haemorrhage in alloimmune fetal thrombocytopenia

Pregnant Women at Low Risk of Having a Child with Fetal and Neonatal Alloimmune Thrombocytopenia Do Not Require Treatment with Intravenous Immunoglobulin

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a rare condition in which maternal alloantibodies to fetal platelets cause fetal thrombocytopenia that may lead to intracranial hemorrhage (ICH). Off-label intravenous immunoglobulin (IVIg) has for 30 years been the standard of care for pregnant women who previously have had a child with FNAIT. The efficacy of this treatment has never been tested in a placebo-controlled clinical trial. Although IVIg treatment may improve the neonatal outcome in women who previously have had a child with FNAIT-associated ICH, the question is whether IVIg is necessary for all immunized pregnant women at risk of having a child with FNAIT. The results from some recent publications suggest that antenatal IVIg treatment is not necessary for women who are (1) HPA-1a-immunized and HLA-DRB3*01:01-negative, (2) HPA-1a-immunized with a previous child with FNAIT but without ICH or (3) HPA-5b-immunized. If IVIg is not used for these categories of pregnant women, the amount of IVIg used in pregnant women with platelet antibodies would be reduced to less than ¼ of today's use. This is important because IVIg is a scarce resource, and the collection of plasma for the treatment of one pregnant woman is not only extremely expensive but also requires tremendous donor efforts.

Preclinical evaluation of immunotherapeutic regimens for fetal/neonatal alloimmune thrombocytopenia

Fetal/neonatal alloimmune thrombocytopenia (FNAIT) is a life-threatening bleeding disorder caused by maternal antibodies directed against paternally inherited antigens present on the surface of fetal platelets. The human platelet alloantigen HPA-1a (formerly known as the PlA1 alloantigen), is the most frequently implicated HPA for causing FNAIT in Whites. A single Leu33Pro amino acid polymorphism residing within the ∼50-amino-acid plexin-semaphorin-integrin domain near the N-terminus of the integrin β3 subunit (platelet membrane glycoprotein IIIa [GPIIIa]) is responsible for generating the HPA-1a and HPA-1b epitopes in human GPIIIa and serves as the central target for alloantibody-mediated platelet destruction. To simulate the etiology of human FNAIT, wild-type female mice were pre-immunized with platelets derived from transgenic mice engineered to express the human HPA-1a epitope on a murine GPIIIa backbone. These mice developed a strong alloimmune response specific for HPA-1a, and when bred with HPA-1a+ males, gave birth to severely thrombocytopenic pups that exhibited an accompanying bleeding phenotype. Administering either polyclonal intravenous immunoglobulin G or a human monoclonal blocking antibody specific for the HPA-1a epitope into pregnant female mice resulted in significant elevation of the neonatal platelet count, normalized hemostasis, and prevented bleeding. The establishment of an alloantigen-specific murine model that recapitulates many of the clinically important features of FNAIT should pave the way for the preclinical development and testing of novel therapeutic and prophylactic modalities to treat or prevent FNAIT in humans.

Risk factors for severity of thrombocytopenia in full term infants: a single center study

Background

Neonatal thrombocytopenia (NT) (platelet count < 150 × 10⁹/L) is a common finding in the neonatal intensive care unit (NICU). The main aim of this study was to assess the prevalence, risk factors, and outcomes of severe NT in full term (FT) infants.

Methods

During the study period, all FT infants who met the inclusion criteria for NT on two occasions were included. Maternal data, such as maternal age, weight, gestational age, mode of delivery, and history of systemic diseases, including diabetes mellitus, pre-eclampsia, systemic lupus erythematosus, and immune thrombocytopenic purpura, were recorded. Furthermore, neonatal data, such as gender, neonatal weight, causes/duration of admission, types of respiratory support used, complete blood count measurements, and outcomes for neonates admitted to the NICU, were recorded.

Results

In total, 55 FT infants with NT met the inclusion criteria, and 29 (52.73%) cases had severe NT. The most common cause of NT was neonatal sepsis (20 cases, 36.35%), followed by a postoperative state (5 cases, 9.09%). Moreover, in cases of positive blood cultures, the most commonly isolated organism was Escherichia coli (6 cases, 10.90%), followed by Klebsiella (5 cases, 9.09%). Cases of severe NT needed more platelet transfusions (P = 0.001) and had higher rates of mortality (P = 0.001) when compared to cases of mild/moderate NT associated with signs of bleeding and pulmonary/intraventricular hemorrhage (IVH) (P = 0.001).

Conclusion

Severe NT compared to mild/moderate NT, associated with signs of bleeding and pulmonary/IVH, needed more platelet transfusions, and had increased mortality. Further research is needed to explain which of these complications related to severity of thrombocytopenia or were associated with original disease of the babies.

High-resolution mapping of the polyclonal immune response to the human platelet alloantigen HPA-1a (PlA1)

Antibodies to platelet-specific antigens are responsible for 2 clinically important bleeding disorders: posttransfusion purpura and fetal/neonatal alloimmune thrombocytopenia (FNAIT). The human platelet-specific alloantigen 1a/1b (HPA-1a/1b; also known as PlA1/A2) alloantigen system of human platelet membrane glycoprotein (GP) IIIa is controlled by a Leu33Pro polymorphism and is responsible for ∼80% of the cases of FNAIT. Local residues surrounding polymorphic residue 33 are suspected to have a profound effect on alloantibody binding and subsequent downstream effector events. To define the molecular requirements for HPA-1a alloantibody binding, we generated transgenic mice that expressed murine GPIIIa (muGPIIIa) isoforms harboring select humanized residues within the plexin-semaphorin-integrin (PSI) and epidermal growth factor 1 (EGF1) domains and examined their ability to support the binding of a series of monoclonal and polyclonal HPA-1a-specific antibodies. Humanizing the PSI domain of muGPIIIa was sufficient to recreate the HPA-1a epitope recognized by some HPA-1a-specific antibodies; however, humanizing distinct amino acids within the linearly distant but conformationally close EGF1 domain was required to enable binding of others. These results reveal the previously unsuspected complex heterogeneity of the polyclonal alloimmune response to this clinically important human platelet alloantigen system. High-resolution mapping of this alloimmune response may improve diagnosis of FNAIT and should facilitate the rational design and selection of contemplated prophylactic and therapeutic anti-HPA-1a reagents.

The Sonographic Detection of Intracranial Hemorrhage Due to Alloimmune Thrombocytopenia

Alloimmune thrombocytopenia is a rare condition in which antibodies from the mother's circulation cross the placenta and destroy the platelets in the fetus. Approximately 14% of affected fetuses or neonates develop intracranial hemorrhage, leading to death or long-term central nervous system disabilities. After treating two such cases, 26 previously reported cases of alloimmune thrombocytopenia with intracranial hemorrhage were examined to discover if these hemorrhages exhibit a typical sonographic appearance, course, and time of hemorrhage. When intracranial hemorrhage occurs in cases of alloimmune thrombocytopenia, it has a typical appearance in 76% of cases: a large hematoma in the center of the cerebral hemisphere. There is no difference between genders in the occurrence of alloimmune thrombocytopenia unless hemorrhage occurs: 72% of neonates with alloimmune thrombocytopenia and intracranial hemorrhage are male. Intracranial hemorrhage occurs before labor and delivery in 76% of cases. Sonographers cannot depend on a history of the condition in previous pregnancies as an indication of alloimmune thrombocytopenia: only 35% of neonates with alloimmune thrombocytopenia and hemorrhage have previously affected siblings.

CRISPR/Cas9-mediated conversion of human platelet alloantigen allotypes

Human platelet alloantigens (HPAs) reside on functionally important platelet membrane glycoproteins and are caused by single nucleotide polymorphisms in the genes that encode them. Antibodies that form against HPAs are responsible for several clinically important alloimmune bleeding disorders, including fetal and neonatal alloimmune thrombocytopenia and posttransfusion purpura. The HPA-1a/HPA-1b alloantigen system, also known as the Pl(A1)/Pl(A2) polymorphism, is the most frequently implicated HPA among whites, and a single Leu33Pro amino acid polymorphism within the integrin β3 subunit is responsible for generating the HPA-1a/HPA-1b alloantigenic epitopes. HPA-1b/b platelets, like those bearing other low-frequency platelet-specific alloantigens, are relatively rare in the population and difficult to obtain for purposes of transfusion therapy and diagnostic testing. We used CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR associated protein 9) gene-editing technology to transform Leu33 (+) megakaryocytelike DAMI cells and induced pluripotent stem cells (iPSCs) to the Pro33 allotype. CD41(+) megakaryocyte progenitors derived from these cells expressed the HPA-1b (Pl(A2)) alloantigenic epitope, as reported by diagnostic NciI restriction enzyme digestion, DNA sequencing, and western blot analysis using HPA-1b-specific human maternal alloantisera. Application of CRISPR/Cas9 technology to genetically edit this and other clinically-important HPAs holds great potential for production of designer platelets for diagnostic, investigative, and, ultimately, therapeutic use.

Platelets and platelet alloantigens: Lessons from human patients and animal models of fetal and neonatal alloimmune thrombocytopenia

Platelets play critical roles in hemostasis and thrombosis. Emerging evidence indicates that they are versatile cells and also involved in many other physiological processes and disease states. Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a life threatening bleeding disorder caused by fetal platelet destruction by maternal alloantibodies developed during pregnancy. Gene polymorphisms cause platelet surface protein incompatibilities between mother and fetus, and ultimately lead to maternal alloimmunization. FNAIT is the most common cause of intracranial hemorrhage in full-term infants and can also lead to intrauterine growth retardation and miscarriage. Proper diagnosis, prevention and treatment of FNAIT is challenging due to insufficient knowledge of the disease and a lack of routine screening as well as its frequent occurrence in first pregnancies. Given the ethical difficulties in performing basic research on human fetuses and neonates, animal models are essential to improve our understanding of the pathogenesis and treatment of FNAIT. The aim of this review is to provide an overview on platelets, hemostasis and thrombocytopenia with a focus on the advancements made in FNAIT by utilizing animal models.

Inhibition of HPA-1a alloantibody-mediated platelet destruction by a deglycosylated anti-HPA-1a monoclonal antibody in mice: toward targeted treatment of fetal-alloimmune thrombocytopenia

Fetal/neonatal alloimmune thrombocytopenia (FNAIT) is often caused by maternal alloantibodies against the human platelet antigen (HPA)-1a, which opsonizes fetal platelets (PLTs). Subsequent PLT destruction is mediated via the Fc part of the alloantibodies. The monoclonal antibody (mAb) SZ21 binds to the HPA-1a epitope and inhibits the binding of maternal alloantibodies. However, it also promotes complement activation and phagocytosis. Deglycosylation of antibodies abrogates the Fc-related effector functions. We modified the N-glycan of SZ21 by endoglycosidase F. The in vivo transplacental transport of N-glycan-modified (NGM)-SZ21 was not impaired. When injected into pregnant mice, both native-SZ21 and NGM-SZ21 were transported equally into fetal circulation (8.9% vs 8.7%, respectively, P = .58). Neither the binding properties of NGM-SZ21 to HPA-1a in surface plasmon resonance, nor the inhibition of anti-HPA-1a-induced PLT phagocytosis, were affected by N-glycan modification. NGM-SZ21 prevented PLT destruction induced by maternal anti-HPA-1a antibodies in vivo in a mouse model (PLT clearance after 5 hours; 18% vs 62%, in the presence or absence of NGM-SZ21, respectively, P = .013). Deglycosylation of SZ21 abrogates Fc-effector functions without interfering with placental transport or the ability to block anti-HPA-1a binding. Humanized, deglycosylated anti-HPA-1a mAbs may represent a novel treatment strategy to prevent anti-HPA-1a-mediated PLT destruction in FNAIT.

Determination of human platelet antigen typing by molecular methods: Importance in diagnosis and early treatment of neonatal alloimmune thrombocytopenia

Neonatal alloimmune thrombocytopenia (NAIT) is the most common cause of severe thrombocytopenia and intracranial hemorrhage in the perinatal period. While the gold standard for making a diagnosis of NAIT is detection of a human platelet antigen (HPA)-specific antibody in maternal serum, together with identifying an incompatibility between the parents for the cognate HPA antigen, platelet genotyping is the gold standard method for HPA typing. Platelet genotyping is critical in screening at-risk fetuses for the presence ofthe HPA corresponding to the maternal antibody. In addition, platelet genotyping may play a role in population screening to identify women at risk for sensitization, and thus, fetuses at risk for NAIT. The most commonly used methods of platelet genotyping are sequence-specific primer-polymerase chain reaction (PCR-SSP), restriction fragment length polymorphism-PCR (PCR-RFLP), and TaqMan real-time PCR. PCR-SSP and PCR-RFLP are relatively inexpensive and technically simple methods, but they are not easily automated and require expertise for reliable interpretation of results. Newer methods that allow for multiplexing, automation, and easily interpretable results, such as bead arrays, are currently in development and available for research purposes.

How I manage neonatal thrombocytopenia

Although neonatal thrombocytopenia (platelet count < 150×10(9) /l) is a common finding in hospital practice, a careful clinical history and examination of the blood film is often sufficient to establish the diagnosis and guide management without the need for further investigations. In preterm neonates, early-onset thrombocytopenia (<72h) is usually secondary to antenatal causes, has a characteristic pattern and resolves without complications or the need for treatment. By contrast, late-onset thrombocytopenia in preterm neonates (>72h) is nearly always due to post-natally acquired bacterial infection and/or necrotizing enterocolitis, which rapidly leads to severe thrombocytopenia (platelet count<50×10(9) /l). Thrombocytopenia is much less common in term neonates and the most important cause is neonatal alloimmune thrombocytopenia (NAIT), which confers a high risk of perinatal intracranial haemorrhage and long-term neurological disability. Prompt diagnosis and transfusion of human platelet antigen-compatible platelets is key to the successful management of NAIT. Recent studies suggest that more than half of neonates with severe thrombocytopenia receive platelet transfusion(s) based on consensus national or local guidelines despite little evidence of benefit. The most pressing problem in management of neonatal thrombocytopenia is identification of safe, effective platelet transfusion therapy and controlled trials are urgently needed.

Reconsidering fetal and neonatal alloimmune thrombocytopenia with a focus on screening and prevention

Uncertainty regarding the pathophysiology of fetal and neonatal alloimmune thrombocytopenia (FNAIT) has hampered the decision regarding how to identify, follow-up and treat the women and children with this potentially serious condition. Since knowledge of the condition is derived mainly from retrospective studies, understanding of the natural history of this condition remains incomplete. General screening programs for FNAIT have still not been introduced, mainly because of a lack of reliable risk factors and effective treatment. Now, several prospective screening studies involving up to 100,000 pregnant women have been published and the results have changed the understanding of the pathophysiology of FNAIT and, thereby, the approach toward diagnostics, prevention and treatment in a more appropriate way.

Repeated intrauterine IgG infusions in foetal alloimmune thrombocytopenia do not increase foetal platelet counts

BACKGROUND AND OBJECTIVES

Foetal alloimmune thrombocytopenia (FNAIT) is often treated transplacentally with maternally administered i.v. immunoglobulins, but not all foetuses show a consistent platelet increase during such treatment.

MATERIALS AND METHODS

We retrospectively analysed data from a cohort of ten foetuses with FNAIT treated by direct foetal immunoglobulin infusion. Foetal treatment was begun between 17 and 25 weeks and continued until 36 weeks with weekly cordocenteses and foetal immunoglobulin infusions.

RESULTS

While foetal IgG levels increased steadily during weekly IgG infusions, foetal platelet counts remained unchanged.

CONCLUSION

Our retrospective study presents a unique analysis of a historical cohort, contributing to the ongoing debate about the treatment of choice for foetal alloimmune thrombocytopenia.

Intracranial hemorrhage in alloimmune thrombocytopenia: stratified management to prevent recurrence in the subsequent affected fetus

OBJECTIVE

We sought to prevent intracranial hemorrhage (ICH) through antenatal management of alloimmune thrombocytopenia.

STUDY DESIGN

A total of 33 women (37 pregnancies) with alloimmune thrombocytopenia and ICH in a previous child were stratified according to the timing of the previous child's ICH: extremely high risk (HR) (n = 8) had ICH <28 weeks, very HR (n = 17) between 28-36 weeks, and HR (n = 12) in the perinatal period. Treatment was initiated at 12 weeks with intravenous immunoglobulin 1 or 2 g/kg/wk, and if the fetal platelet count by cordocentesis was <30,000/mL despite treatment, prednisone and/or more intravenous immunoglobulin were added.

RESULTS

Five of 37 fetuses suffered ICHs. Two ICHs had platelet counts >100,000/mL, and 1 was grade I. The other 2 ICHs were unequivocal treatment failures; both were grade III-IV and resulted in fetal demise.

CONCLUSION

These findings demonstrate the success of stratified treatment in these HR patients, which tailored interventions according to the timing of the sibling's ICH.

Fetal alloimmune thrombocytopenia and maternal intravenous immunoglobulin infusion

BACKGROUND

Different therapeutic approaches have been used in fetal-neonatal alloimmune thrombocytopenia, but many centers administer immunoglobulin G infusions to the pregnant woman. We studied the effect of maternal antenatal immunoglobulin infusions on fetal platelet counts in pregnancies with fetal alloimmune thrombocytopenia.

DESIGN AND METHODS

We retrospectively analyzed the clinical courses of fetuses with fetal alloimmune thrombocytopenia whose mothers were treated with immunoglobulin G infusions in a single center between 1999 and 2005. In a center-specific protocol, weekly maternal immunoglobulin G infusions were given to 25 pregnant women with previously affected neonates and four women with strong platelet antibodies, but no previous history of fetal alloimmune thrombocytopenia; before each infusion diagnostic fetal blood sampling was performed to determine fetal platelet counts and immunoglobulin G levels.

RESULTS

There were 30 fetuses with fetal alloimmune thrombocytopenia, confirmed by initial fetal blood sampling showing fetal platelet counts between 4×10(9)/L and 130×10(9)/L and antibody-coated fetal platelets using a glycoprotein specific assay. Despite weekly antenatal maternal immunoglobulin G infusions fetal platelet counts did not change significantly. Maternal and fetal immunoglobulin G levels, measured before every infusion, increased significantly with the number of maternal immunoglobulin G infusions.

CONCLUSIONS

In this group of fetuses with fetal alloimmune thrombocytopenia no consistent increase of fetal platelets was achieved as a result of regular maternal immunoglobulin G infusions.

Neonatal alloimmune thrombocytopenia is not what it was: a lesson learned from a large prospective screening and intervention program

Controversies regarding the pathophysiology of neonatal alloimmune thrombocytopenia (NAIT) has hampered the development of consensus about how to identify, follow up and treat the women and children with this serious complication. One reason for this is that knowledge about the condition derived from previous retrospective studies do not necessarily conform with data derived from prospective investigations. The main obstacle to introduction of general screening programs to identify the pregnancies to treat, have been lack of reliable risk factors, and an effective treatment. Now, several recent prospective screening programs including up to 100,000 pregnant women has changed the understanding of the NAIT-pathology, and has shown that we are close to answering these critical questions.

Developing recombinant HPA-1a-specific antibodies with abrogated Fcgamma receptor binding for the treatment of fetomaternal alloimmune thrombocytopenia

Fetomaternal alloimmune thrombocytopenia (FMAIT) is caused by maternal generation of antibodies specific for paternal platelet antigens and can lead to fetal intracranial hemorrhage. A SNP in the gene encoding integrin beta3 causes a clinically important maternal-paternal antigenic difference; Leu33 generates the human platelet antigen 1a (HPA-1a), whereas Pro33 generates HPA-1b. As a potential treatment to prevent fetal intracranial hemorrhage in HPA-1a alloimmunized pregnancies, we generated an antibody that blocks the binding of maternal HPA-1a-specific antibodies to fetal HPA-1a1b platelets by combining a high-affinity human HPA-1a-specific scFv (B2) with an IgG1 constant region modified to minimize Fcgamma receptor-dependent platelet destruction (G1Deltanab). B2G1Deltanab saturated HPA-1a+ platelets and substantially inhibited binding of clinical HPA-1a-specific sera to HPA-1a+ platelets. The response of monocytes to B2G1Deltanab-sensitized platelets was substantially less than their response to unmodified B2G1, as measured by chemiluminescence. In addition, B2G1Deltanab inhibited chemiluminescence induced by B2G1 and HPA-1a-specific sera. In a chimeric mouse model, B2G1 and polyclonal Ig preparations from clinical HPA-1a-specific sera reduced circulating HPA-1a+ platelets, concomitant with transient thrombocytopenia. As the Deltanab constant region is uninformative in mice, F(ab')2 B2G1 was used as a proof of principle blocking antibody and prevented the in vivo platelet destruction seen with B2G1 and polyclonal HPA-1a-specific antibodies. These results provide rationale for human clinical studies.

Neonatal thrombocytopenia

Thrombocytopenia (platelets <150 x 10(9)/L) is one of the most common haematological problems in neonates, particularly those who are preterm and sick. In those preterm neonates with early thrombocytopenia who present within 72 h of birth, the most common cause is reduced platelet production secondary to intrauterine growth restriction and/or maternal hypertension. By contrast, the most common causes of thrombocytopenia arising after the first 72 h of life, both in preterm and term infants, are sepsis and necrotizing enterocolitis. The most important cause of severe thrombocytopenia (platelets <50 x 10(9)/L) is neonatal alloimmune thrombocytopenia (NAIT), as diagnosis can be delayed and death or long-term disability due to intracranial haemorrhage may occur. Platelet transfusion is the mainstay of treatment for severe thrombocytopenia. However, the correlation between thrombocytopenia and bleeding is unclear and no studies have yet shown clinical benefit for platelet transfusion in neonates. Studies to identify optimal platelet transfusion practice for neonatal thrombocytopenia are urgently required.

Thrombocytopenia in the neonate

Thrombocytopenia is one of the commonest haematological problems in neonates, affecting at least 25% of all admissions to neonatal intensive care units (NICUs) [Murray NA, Howarth LJ, McCloy MP et al. Platelet transfusion in the management of severe thrombocytopenia in neonatal intensive care unit patients. Transfus Med 2002;12:35-41; Garcia MG, Duenas E, Sola MC et al. Epidemiologic and outcome studies of patients who received platelet transfusions in the neonatal intensive care unit. J Perinatol 2001;21:415-20; Del Vecchio A, Sola MC, Theriaque DW et al. Platelet transfusions in the neonatal intensive care unit: factors predicting which patients will require multiple transfusions. Transfusion 2001;41:803-8]. Although a long list of disorders associated with neonatal thrombocytopenia can be found in many textbooks, newer classifications based on the timing of onset of thrombocytopenia (early vs. late) are more useful for planning diagnostic investigations and day-to-day management. The mainstay of treatment of neonatal thrombocytopenia remains platelet transfusion although it is important to note that no studies have yet shown clinical benefit of platelet transfusion in this setting. Indeed some reports even suggest that there may be significant adverse effects of platelet transfusion in neonates, including increased mortality, and that the effects of transfusion may differ in different groups of neonates with similar degrees of thrombocytopenia [Bonifacio L, Petrova A, Nanjundaswamy S, Mehta R. Thrombocytopenia related neonatal outcome in preterms. Indian J Pediatr 2007;74:269-74; Kenton AB, Hegemier S, Smith EO et al. Platelet transfusions in infants with necrotizing enterocolitis do not lower mortality but may increase morbidity. J Perinatol 2005;25:173-7]. There is also considerable variation in transfusion practice between different countries and between different neonatal units. Here we review recent progress in understanding the prevalence, causes and pathogenesis of thrombocytopenia in the newborn, the clinical consequences of thrombocytopenia and developments in neonatal platelet transfusion.

Fetal and neonatal alloimmune thrombocytopenia: progress and ongoing debates

Fetal and neonatal alloimmune thrombocytopenia (AIT) is a result of a parental incompatibility of platelet-specific antigens and the transplacental passage of maternal alloantibodies against the platelet antigen shared by the father and the fetus. It occurs in approximately 1 in 1000 live births and is the most common cause of severe thrombocytopenia in fetuses and term neonates. As screening programs are not routinely performed, most affected fetuses are identified after birth when neonatal thrombocytopenia is recognized. In severe cases, the affected fetus is identified as a result of suffering from an in utero intracranial hemorrhage. Once diagnosed, AIT must be treated antenatally as the disease can be more severe in subsequent pregnancies. While there have been many advances regarding the diagnosis and treatment of AIT, it is still difficult to predict the severity of disease and which therapy will be effective.

HPA-1a antibody potency and bioactivity do not predict severity of fetomaternal alloimmune thrombocytopenia

BACKGROUND

The antenatal management of fetomaternal alloimmune thrombocytopenia (FMAIT) due to HPA-1a antibodies remains controversial, and a test identifying pregnancies that do not require therapy would be of clinical value.

STUDY DESIGN AND METHODS

The statistical correlation was analyzed between clinical outcome and 1) anti-HPA-1a potency in maternal serum samples determined by a monoclonal antibody immobilization of platelet (PLT) antigen assay with an international anti-HPA-1a potency standard and 2) anti-HPA-1a biological activity measured by a monocyte chemiluminescence (CL) assay.

RESULTS

A total of 133 pregnancies with FMAIT due to anti-HPA-1a were analyzed. In 97 newly diagnosed cases, there was no difference in antibody potency or CL signal between cases with intracranial hemorrhage (ICH; n = 15), those with no ICH but a PLT count of less than 20 x 10(9) per L (n = 52), and those with a PLT count of at least 20 x 10(9) per L (n = 30). In 22 previously known pregnancies, the positive predictive value of maternal anti-HPA-1a of greater than 30 IU per mL for a PLT count of less than 20 x 10(9) per L was 90 percent, but the negative predictive value was only 66 percent. Antibody potency tended to stay stable throughout pregnancy (n = 16) and from one pregnancy to the next (n = 16).

CONCLUSION

Neither severe thrombocytopenia nor ICH in HPA-1a-alloimmunized pregnancies can be predicted with sufficient sensitivity and specificity for clinical application from maternal anti-HPA-1a potency or bioactivity.

Management and outcome of 200 cases of fetomaternal alloimmune thrombocytopenia

BACKGROUND

Fetomaternal alloimmune thrombocytopenia (FMAIT) is the commonest cause of severe thrombocytopenia in term neonates but its management remains controversial.

STUDY DESIGN AND METHODS

A 7-year prospective observational study of 200 cases of FMAIT evaluated the relationship between human platelet antigen (HPA) antibody specificity, clinical presentation, morbidity, mortality, and therapeutic interventions in the antenatal and postnatal period, with long-term follow-up of neonates with intracranial hemorrhage (ICH).

RESULTS

In 1148 referrals for FMAIT, HPA antibodies were confirmed in 200 (17%). The commonest specificities were anti-HPA-1a, 150 (75%); anti-HPA-5b, 31 (15.5%); and anti-HPA-15b, 8 (4%). Of 123 (62%) cases (two sets of twins) with no previous history of FMAIT, intrauterine deaths occurred in 5: anti-HPA-1a alone, 3; in combination with anti-HPA-5b, 1; and anti-HPA-15b, 1. Of the 120 live neonates, 103 had severe thrombocytopenia and 17 (14%) developed ICH (anti-HPA-1a, 13; anti-HPA-5b, 3; anti-HPA-15b, 1). Postnatal care varied widely with 37 percent of neonates receiving random rather than HPA-1a and -5b-negative platelets. Of the remaining 77 cases with a history of FMAIT, 40 received intrauterine transfusions. Six (15%) of these fetuses died in utero and an additional 2 developed ICH postnatally. Of the 19 children with ICH, 1 (anti-HPA-15b) died on Day +1, and neurologic sequelae persist in 13 (mean follow-up, 2.5 years).

CONCLUSION

HPA-1a antibodies are most commonly implicated in severe thrombocytopenia but HPA-5b and HPA-15b antibodies can also result in poor outcome. Postnatal transfusion management is extremely variable, and fetal transfusions are associated with significant morbidity and mortality.

Advances in the management of alloimmune thrombocytopenia

There have been considerable advances in the clinical and laboratory diagnosis of alloimmune thrombocytopenia (AIT), and its postnatal and antenatal management. The antenatal management of AIT has been particularly problematic, because severe haemorrhage occurs as early as 16 weeks gestation and there is no non-invasive investigation that reliably predicts the severity of AIT in utero. The strategies for antenatal treatment have included the use of serial platelet transfusions that, while effective, are invasive and associated with significant morbidity and mortality. Maternal therapy involving the administration of intravenous immunoglobulin and/or steroids is also effective and associated with fewer risks to the fetus. Significant recent progress has involved refinement of maternal treatment, stratifying it according to the likely severity of AIT based on the history in previous pregnancies. However, the ideal antenatal treatment, which is effective without causing significant side-effects to the mother or fetus, has yet to be determined, and further clinical trials are needed.

[Is a non-invasive management allowed for maternofetal alloimmune thrombocytopenia? Experience over a 10-year period]

OBJECTIVES

Our purpose was to study a non-invasive management of fetomaternal alloimmune thrombocytopenia (FMAIT).

PATIENTS AND METHODS

Between 1996 and 2005, 18 women were treated. The population was divided into 2 groups: patients with a history of intracranial haemorrhage (ICH) in the older sibling received weekly intravenous immunoglobulin (IVIG) therapy to the mother (1 g/kg per week) without initial cordocentesis whereas patients with a history of neonatal thrombocytopenia did not undergo any treatment.

RESULTS

All pregnancies with a previous FMAIT were monitored with serial ultrasound scans without cordecentesis. 15 patients had HPA-1, 2 HPA-3 and 1 HPA-5 immunizations. Weekly intravenous immunoglobulin therapy was administered in 5 patients with a history of ICH in the older sibling. Two of these delivered thrombocytopenic children; one had a platelet count < 50 x 10(9)/l. For the 13 women (one twin) who had a sibling with neonatal thrombocytopenia, 11/14 newborns had a platelet count < 50 x 10(9)/l. Predelivery fetal blood sampling were performed in 8/18 pregnancies. The neonatal periods of the 19 children were uncomplicated and no ICHs were observed.

DISCUSSION AND CONCLUSION

Our results suggest that a non-invasive strategy avoiding serial cordocentesis may be an effective therapy in patients who are at risk of fetal and neonatal alloimmune thrombocytopenia.

Foetal and neonatal alloimmune thrombocytopaenia

Foetal/neonatal alloimmune thrombocytopaenia (NAIT) results from maternal alloimmunisation against foetal platelet antigens inherited from the father and different from those present in the mother, and usually presents as a severe isolated thrombocytopaenia in otherwise healthy newborns. The incidence has been estimated at 1/800 to 1/1000 live births. NAIT has been considered to be the platelet counterpart of Rh Haemolytic Disease of the Newborn (RHD). Unlike RHD, NAIT can occur during a first pregnancy. The spectrum of the disease may range from sub-clinical moderate thrombocytopaenia to life-threatening bleeding in the neonatal period. Mildly affected infants may be asymptomatic. In those with severe thrombocytopaenia, the most common presentations are petechiae, purpura or cephalohaematoma at birth, associated with major risk of intracranial haemorrhage (up to 20% of reported cases), which leads to death or neurological sequelae. Alloimmune thrombocytopaenia is more often unexpected and is usually diagnosed after birth. Once suspected, the diagnosis is confirmed by demonstration of maternal antiplatelet alloantibodies directed against a paternal antigen inherited by the foetus/neonate. Post-natal management involves transfusion of platelets devoid of this antigen, and should not be delayed by biological confirmation of the diagnosis (once the diagnosis is suspected), especially in case of severe thrombocytopaenia. Prompt diagnosis and treatment are essential to reduce the chances of death and disability due to haemorrhage. Due to the high rate of recurrence and increased severity of the foetal thrombocytopaenia in successive pregnancies, antenatal therapy should be offered. However, management of high-risk pregnancies is still a matter of discussion.

Management of bleeding disorders in children

Diagnosis and management of congenital and acquired bleeding disorders in children requires not only an understanding of the unique characteristics of pediatric hemostasis but also the natural course of bleeding disorders in children, which may differ substantially from the course observed in adult patients. In this article, three bleeding disorders of great importance to the pediatric hematologist are reviewed: neonatal alloimmune thrombocytopenia (NAIT), hemophilia and immune-mediated thrombocytopenic purpura (ITP). Current aspects of management are outlined. The unique physiology of transplacental transfer of maternally derived anti-platelet antibodies can result in neonatal immune thrombocytopenia, a significant cause of morbidity and mortality from bleeding in affected infants. For patients with hemophilia, approaches to treatment have shifted over the past decade from on-demand therapy to prophylaxis, either primary of secondary, resulting in delay of onset or complete avoidance of hemophilic arthropathy. Hemophilic inhibitors often develop in young children, prompting the need for a thorough understanding of the use of bypassing agents as well as immune tolerance induction in the young child. Finally, although several management strategies for ITP of childhood have been shown to improve the platelet count, side effects associated with corticosteroids, IVIg, anti-D and splenectomy force the practitioner to also consider the option of carefully observing, but not treating, the child with ITP.

Longitudinal thrombopoietin plasma concentrations in fetuses with alloimmune thrombocytopenia treated with intrauterine PLT transfusions

BACKGROUND

The purpose of this study was to describe longitudinal thrombopoietin (TPO) plasma concentrations in fetuses with fetomaternal alloimmune thrombocytopenia (FMAIT).

STUDY DESIGN AND METHODS

Group 1 was the control group, 8 fetuses with normal hematopoiesis. Group 2 consisted of 4 nonthrombocytopenic fetuses with fetomaternal human PLT antigen incompatibility. Group 3 consisted of 14 fetuses with prenatal-diagnosed severe FMAIT owing to human PLT antigen-1a incompatibility. Fetal PLT counts, MoAb-specific immobilization of PLT antigen score, and TPO plasma concentrations were measured in a total number of 94 serial samples taken by cordocentesis before intrauterine PLT transfusion.

RESULTS

Normal fetal TPO plasma concentrations ranged between 15 and 119 pg per mL (Group 1 median, 67 pg/mL). In fetuses with risk of FMAIT but normal PLT counts, TPO concentrations were normal (Group 2 median, 72 pg/mL; range, <15-158 pg/mL). In FMAIT with thrombocytopenia, the median TPO concentration was significantly higher than in Groups 1 and 2 (Group 3 median, 172 pg/mL; range, 15-623 pg/mL; p < 0.001). In the longitudinal analysis, TPO concentrations remained constant (n = 8), peaked only transiently (n = 3), or increased at the end of gestation (n = 3). Elevated TPO concentrations (592 and 623 pg/mL) were detected in one patient, who already had intracranial hemorrhage in utero.

CONCLUSION

TPO concentrations are normal or slightly elevated in FMAIT. Further clinical information can be provided by the longitudinal analysis of TPO concentrations in severe FMAIT.

Outcome of antenatally diagnosed intracranial hemorrhage: case series and review of the literature

OBJECTIVES

Prenatal diagnosis of intracranial hemorrhage (ICH) has been widely reported. Hemorrhages may occur either within the cerebral ventricles, subdural space or infratentorial fossa. The aim of this study was to determine the sonographic criteria for the diagnosis of fetal ICH, the role of in utero magnetic resonance imaging (MRI) and the outcome of this condition.

METHODS

The archives of our ultrasound laboratory and the literature were searched for all cases of antenatally diagnosed ICH. A grading system was used to classify the intraventricular lesions as suggested in postnatal sonographic studies.

RESULTS

Adding our series of 16 fetuses to the 93 cases identified in the literature, a group of 109 fetal ICHs was obtained: 89 were intracerebral (79 intraventricular and 10 infratentorial) and 20 were subdural hemorrhages. Intraventricular lesions were mostly classified as severe (32 each for Grades III and IV). In 27 cases antenatal MRI was performed additionally to ultrasound and confirmed the sonographic findings. Of the entire group, 65 infants (59%) were reported to be alive 1 month after birth (51 intraventricular hemorrhages, three infratentorial hemorrhages, 11 subdural hematomas). At 12 months, of the 48 infants whose follow-up was available, 25 or 52% were judged neurologically normal (17/36 or 47% among the intraventricular hemorrhages, 6/9 or 66% among the hematomas, and 2/3 or 66% among the infratentorial hemorrhages).

CONCLUSIONS

Fetal ICH may be accurately identified and categorized by antenatal sonography. The outcome is usually poor, especially for those fetuses affected by higher-grade intraventricular hemorrhages.

Will it ever be possible to balance the risk of intracranial haemorrhage in fetal or neonatal alloimmune thrombocytopenia against the risk of treatment strategies to prevent it?

BACKGROUND AND OBJECTIVES

Intracranial haemorrhage (ICH) of the fetus or newborn is a severe complication of fetal or neonatal alloimmune thrombocytopenia (FNAIT). In order to attain management decisions to prevent ICH, the risk of ICH in successive pregnancies with thrombocytopenia, with or without a history of ICH, must be established.

MATERIALS AND METHODS

We performed a search of medline for ICH cases in untreated FNAIT pregnancies. After exclusion of cases with confounding factors, 24 reports, describing 62 pregnancies of 27 mothers, were eligible. In addition, two mothers with five pregnancies were included from our own case records. Observational studies were examined to estimate the risk of ICH in subsequent FNAIT pregnancies without a history of ICH. Finally, medline was searched for complication rates in the treatment of FNAIT pregnancies.

RESULTS

In 52% of the ICH cases, a previous sibling suffered from ICH. The recurrence rate of ICH in the subsequent offspring of women with a history of FNAIT with ICH was 72%[confidence interval (CI): 46-98%] without inclusion of fetal deaths and 79% (CI: 61-97%) with inclusion of fetal deaths. In 48% of the ICH cases, the previous sibling had thrombocytopenia but not ICH. Population studies revealed an overall ICH risk in thrombocytopenic infants of 11% (CI: 0.8-23%) without inclusion of fetal deaths and 15% (CI: 1.5-19%) with inclusion of fetal deaths. Assuming occurrence in 48%, the risk of ICH in a subsequent pregnancy following a history of FNAIT without ICH, was estimated to be 7% (CI: 0.5-13%). Invasive treatment strategies carry a risk of 2.8% (CI: 1.2-4.4%) on complications.

CONCLUSIONS

The number of eligible publications on ICH in untreated FNAIT pregnancies is strikingly limited. The recurrence rate is high. As sufficient data on successive FNAIT cases without ICH are lacking, the occurrence of ICH in pregnancies with thrombocytopenia, but without ICH in a previous sibling, cannot be predicted. We estimate this risk to be 7%. This risk must be balanced against the risk of interventions in treatment strategies.

A less invasive treatment strategy to prevent intracranial hemorrhage in fetal and neonatal alloimmune thrombocytopenia

OBJECTIVE

The purpose of this study was to evaluate whether a less invasive treatment strategy results in a higher platelet count of the neonate and prevents intracranial hemorrhage in pregnant women who are at risk for fetal or neonatal alloimmune thrombocytopenia.

STUDY DESIGN

Between March 1989 and August 2000, 48 women with 56 pregnancies were treated. The population was divided into groups. A diagnostic fetal blood sample was taken in 7 cases that had a history of a sibling with an intracranial hemorrhage (group I; n = 8); treatment was provided, when necessary, with platelet transfusions and maternal administration of immunoglobulin. The other 48 cases, with a history of a sibling with severe thrombocytopenia but without intracranial hemorrhage, were retrospectively divided into group IIa (n = 16) and IIb (n = 32). In group IIa, at least 2 diagnostic fetal blood samples were taken, and when necessary, intrauterine platelet transfusion and immunoglobulin were administered (invasive treatment). In group IIb, no initial diagnostic fetal blood sampling was performed (noninvasive treatment). In 23 cases, immunoglobulin was administered, which was followed by predelivery fetal blood sampling in 8 cases. In 9 cases, only predelivery fetal blood sampling was performed, when necessary, followed by intrauterine platelet transfusion.

RESULTS

Results of our noninvasive treatment strategy were comparable to results of the invasive method in the prevention of intracranial hemorrhage (intracranial hemorrhage was not observed). In addition, there was an increasing trend in median platelet count and a lower number of cases with severe thrombocytopenia (<50 x 10(9)/L) in the noninvasive compared with the invasive treatment group (median platelet count, 92 and 31 x 10(9)/L, respectively).

CONCLUSION

Our results indicate that a less invasive treatment strategy in patients who are at risk for fetal or neonatal alloimmune thrombocytopenia and who have no history of a previous child who was affected with intracranial hemorrhage seems justified.

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.

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.

Neonatal alloimmune thrombocytopenia: antenatal management

OBJECTIVE

The optimal management of pregnancies at risk for neonatal alloimmune thrombocytopenia is debated. Proposed management includes the administration of intravenous immunoglobulin and serial determination of the fetal platelet count. The aims of our study were to determine the effectiveness and likely mechanism of action of intravenous immunoglobulin and to evaluate the safety of cordocentesis in cases of neonatal alloimmune thrombocytopenia.

STUDY DESIGN

Eighteen mother-infant pairs were studied. All were at risk for neonatal alloimmune thrombocytopenia on the basis of delivery of a previously affected infant and confirmation of specific maternal antiplatelet antibodies. The pertinent antigen was HPA-1a in 13 cases, HPA-3a in 2 cases, and undetermined in 3 cases. Serial cordocenteses were used to determine fetal platelet counts. If the platelet count was <50,000/microL before 37 weeks' gestation, treatment was initiated with intravenous immunoglobulin administered to either the fetus (n = 2) or the mother (n = 8). In 3 cases fetal and maternal immunoglobulin G levels were determined before and after treatment.

RESULTS

Seven (39%) fetuses had adequate platelet counts, were not treated, and were delivered of infants with normal platelet counts. Eleven (61%) fetuses were thrombocytopenic. Eight thrombocytopenic infants were treated with maternally administered intravenous immunoglobulin. In 6 (75%) of 8 cases the fetal platelet count increased after administration of intravenous immunoglobulin, but 2 fetuses remained severely thrombocytopenic. Two thrombocytopenic fetuses were treated with intravenous immunoglobulin infusion directly into the umbilical vein; both remained thrombocytopenic. Moreover, fetal immunoglobulin G levels did not correlate well with the response to intravenous immunoglobulin. Two (5.3%) of 38 cordocenteses were complicated by hemorrhagic complications, necessitating immediate cesarean delivery despite the use of prophylactic platelet transfusion in one case.

CONCLUSION

Severe fetal alloimmune thrombocytopenia does not always occur in subsequent fetuses. Thus either fetal antigen status or platelet counts or both of these are necessary to determine whether treatment is needed. The effect of intravenous immunoglobulin on raising the fetal platelet count is inconsistent and appears to be caused by maternal or placental factors rather than a direct inhibition of fetal platelet destruction by immunoglobulin. The risk of hemorrhagic complications from cordocentesis in pregnancies complicated by neonatal alloimmune thrombocytopenia is higher than generally appreciated and is not always avoided by platelet transfusion at the time of the procedure.

Clinical uses of intravenous immunoglobulin in pregnancy

The obstetric literature contains numerous reports of IVIG therapy for various conditions encountered during pregnancy. The mechanisms of action of IVIG are uncertain and may vary depending on the specific disorder. Immunoglobulin G infusions appear to be well tolerated by the parturient. The occurrence of major and minor side effects is uncommon, and infectious morbidity is low. Further research will be necessary to elucidate the specific mechanisms of action of IVIG in certain disease states. Determining the exact "therapeutic agent" in IVIG for each specific disease state may allow for a more tailored approach to treatment (i.e., isolation or production of the particular antibody). Outcome assessment, long-term positive and negative effects, cost-benefit analysis, and effects on fetal and neonatal immune function require further study through randomized trials.

The Natural History of Fetomaternal Alloimmunization to the Platelet-Specific Antigen HPA-1a (PlA1, Zwa) as Determined by Antenatal Screening

Immunization against the human platelet antigen (HPA)-1 alloantigen is the most common cause of severe fetal and neonatal thrombocytopenia. Fetal therapy has substantial risks and its indications need better definition. Of 24,417 consecutive pregnant women, 618 (2.5%) were HPA-1a negative of whom 385 entered an observational study. All were HLA-DRB3*0101 genotyped and screened for anti–HPA-1a. Their partners and neonates were HPA-1 genotyped and the latter were assessed by cord blood platelet counts and cerebral ultrasound scans. Anti–HPA-1a was detected in 46 of 387 pregnancies (12.0%; 95% CI 8.7%-15.2%). All but one were HLA-DRB3*0101 positive (odds ratio 140; 95% CI 19-1035;P< .00001). One baby died in utero, and of 26 HPA-1a–positive babies born to women with persistent antenatal antibodies, 9 were severely thrombocytopenic (8 with a count <10 × 109/L, 1 with a large porencephalic cyst), 10 were mildly thrombocytopenic, whereas 7 had normal platelet counts. Severe thrombocytopenia was significantly associated with a third trimester anti–HPA-1a titer ≥ 1:32 (P = .004), but was not observed in babies of women with either transient or postnatal-only antibodies. HPA-1a alloimmunization complicates 1 in 350 unselected pregnancies, resulting in severe thrombocytopenia in 1:1,200. HPA-1a and HLA-DRB3*0101 typing combined with anti–HPA-1a titration allows selection of the majority of pregnancies at risk of severe thrombocytopenia.

The Natural History of Fetomaternal Alloimmunization to the Platelet-Specific Antigen HPA-1a (PlA1, Zwa) as Determined by Antenatal Screening

Immunization against the human platelet antigen (HPA)-1 alloantigen is the most common cause of severe fetal and neonatal thrombocytopenia. Fetal therapy has substantial risks and its indications need better definition. Of 24,417 consecutive pregnant women, 618 (2.5%) were HPA-1a negative of whom 385 entered an observational study. All were HLA-DRB3*0101 genotyped and screened for anti–HPA-1a. Their partners and neonates were HPA-1 genotyped and the latter were assessed by cord blood platelet counts and cerebral ultrasound scans. Anti–HPA-1a was detected in 46 of 387 pregnancies (12.0%; 95% CI 8.7%-15.2%). All but one were HLA-DRB3*0101 positive (odds ratio 140; 95% CI 19-1035;P< .00001). One baby died in utero, and of 26 HPA-1a–positive babies born to women with persistent antenatal antibodies, 9 were severely thrombocytopenic (8 with a count <10 × 109/L, 1 with a large porencephalic cyst), 10 were mildly thrombocytopenic, whereas 7 had normal platelet counts. Severe thrombocytopenia was significantly associated with a third trimester anti–HPA-1a titer ≥ 1:32 (P = .004), but was not observed in babies of women with either transient or postnatal-only antibodies. HPA-1a alloimmunization complicates 1 in 350 unselected pregnancies, resulting in severe thrombocytopenia in 1:1,200. HPA-1a and HLA-DRB3*0101 typing combined with anti–HPA-1a titration allows selection of the majority of pregnancies at risk of severe thrombocytopenia.

Screening programmes for foetomaternal alloimmune thrombocytopenia

Screening to detect pregnancies at risk of severe thrombocytopenia due to Foetomaternal alloimmunisation to Human Platelet Alloantigens (FAIT) is not yet a standard of care. Screening may be performed antenatally with the possibility of early intervention/therapy. Post natal measurement of cord platelet count may not always prevent fetal damage but may detect severe thrombocytopenia from other causes. Assessment of FAIT screening against World Health Organisation standards for screening programmes helps define areas where knowledge is still lacking and where research effort should be directed. Limitations to screening have been lack of reliable assays for typing and antibody detection, a limited understanding of the relationship between the presence of alloantibodies and clinical disease, inability to predict non-invasively which cases will have a severe outcome, and controversy as to which antenatal therapy is optimal for cases at high risk of a poor outcome.

Fetal thrombocytopenia

In idiopathic thrombocytopenic purpura, the low risk of fetal bleeding in the perinatal period does not justify routine cordocentesis. Platelet counts of second newborns correlates well with that of their siblings. In neonatal alloimmune thrombocytopenia, the initial platelet count at cordocentesis in the second trimester is low in the next pregnancy. Weekly high doses of intravenous gammaglobulin to the mother results in a rise of fetal platelet count in approximately 70% of cases and may protect the fetus against intracranial haemorrhage in cases without significant platelet rise. With the exception of cases with a prior infant with spontaneous fetal intracranial haemorrhage, the use of diagnostic fetal blood sampling to confirm neonatal alloimmune thrombocytopenia is controversial.