Alloimmunization to the PlA1 platelet antigen: results of a prospective study

Natural history of human platelet antigen 1a-alloimmunised pregnancies: a prospective observational cohort study

BACKGROUND

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a rare disease that untreated can lead to intracranial haemorrhage or death. The natural history of FNAIT is still unclear; therefore, the benefits of screening cannot be estimated and no routine screening is yet in place. We aimed to assess the incidence of clinically detectable FNAIT among pregnancies in human platelet antigen-1a (HPA-1a)-immunised women.

METHODS

We did a prospective observational cohort study of pregnant women negative for rhesus D (RhD) and rhesus c (Rhc) antigens, without age limits, who underwent routine antenatal screening for red cell antibodies at 27 weeks' gestation and were typed for HPA-1a between March 1, 2017, and May 1, 2020. HPA-1a-negative women were tested for HPA alloantibodies. Health-care professionals were masked to all test results. The main outcome was the proportion of neonates with severe, clinically detectable FNAIT, defined as having an intracranial bleed, organ bleed, or bleeding-related death observed during pregnancy or within the first week of life. Cases of clinically detectable FNAIT not categorised as severe were categorised as mild. This study is registered with ClinicalTrials.gov (NCT04067375).

FINDINGS

Of 153 106 women typed for HPA-1a, 3722 (2·4%) were negative for HPA-1a. 913 HPA-1a-negative women gave informed consent, underwent HPA-1a antibody screening, and were included in the study. Anti-HPA-1a antibodies were detected in 85 HPA-1a-negative participants, among whom three with HPA-1a-negative fetuses and one with a previous child with FNAIT were excluded. As controls, 820 HPA-1a-negative, non-immunised pregnancies and 2704 randomly selected pregnancies of women negative for RhD and Rhc who were typed HPA-1a positive were included. Of 81 fetuses included, one (1·2%) was diagnosed with severe HPA-1a-mediated intracranial haemorrhage and three (3·7%) had mild FNAIT. Gravidity and parity did not seem to be risk factors for HPA-1a immunisation. 73 (90·1%) of 81 HPA-1a-immunised women were positive for HLA-DRB3*01:01.

INTERPRETATION

Our data suggest that, without intervention, the incidence of major clinically detectable bleeding in FNAIT is estimated as 11 (95% CI 0-32) per 10 000 HPA-1a-negative pregnancies. These findings imply that severe bleeding is a rare event that potentially could be prevented by a screening programme.

FUNDING

Landsteiner Foundation for Blood Transfusion Research and Sanquin.

Maternal and foetal outcomes following natural vaginal versus caesarean section (c-section) delivery in women with bleeding disorders and carriers

BACKGROUND

Bleeding disorders are uncommon but may pose significant bleeding complications during pregnancy, labour and following delivery for both the woman and the foetus. While many bleeding disorders in women tend to improve in pregnancy, thus decreasing the haemorrhagic risk to the mother at the time of delivery, some do not correct or return quite quickly to their pre-pregnancy levels in the postpartum period. Therefore, specific measures to prevent maternal bleeding and foetal complications during childbirth, are required. The safest method of delivery to reduce morbidity and mortality in these women is controversial. This is an update of a previously published review.

OBJECTIVES

To assess the optimal mode of delivery in women with, or carriers of, bleeding disorders.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Coagulopathies Trials Register, compiled from electronic database searches and handsearching of journals and conference abstract books. We also searched the Cochrane Pregnancy and Childbirth Group's Trials Register as well as trials registries and the reference lists of relevant articles and reviews. Date of last search of the Group's Trials Registers: 21 June 2021.

SELECTION CRITERIA

Randomised controlled trials and quasi-randomised controlled clinical trials investigating the optimal mode of delivery in women with, or carriers of, any type of bleeding disorder during pregnancy were eligible for the review.

DATA COLLECTION AND ANALYSIS

No trials matching the selection criteria were eligible for inclusion.

MAIN RESULTS

No trials matching the selection criteria were eligible for inclusion.

AUTHORS' CONCLUSIONS

The review did not identify any randomised controlled trials investigating the safest mode of delivery and associated maternal and foetal complications during delivery in women with, or carriers of, a bleeding disorder. In the absence of high quality evidence, clinicians need to use their clinical judgement and lower level evidence (e.g. from observational trials, case studies) to decide upon the optimal mode of delivery to ensure the safety of both mother and foetus. Given the ethical considerations, the rarity of the disorders and the low incidence of both maternal and foetal complications, future randomised controlled trials to find the optimal mode of delivery in this population are unlikely to be carried out. Other high quality controlled studies (such as risk allocation designs, sequential design, and parallel cohort design) are needed to investigate the risks and benefits of natural vaginal and caesarean section in this population or extrapolation from other clinical conditions that incur a haemorrhagic risk to the baby, such as platelet alloimmunisation.

Hemostatic Challenges in Neonates

The neonatal hemostatic system is strikingly different from that of adults. Among other differences, neonates exhibit hyporeactive platelets and decreased levels of coagulation factors, the latter translating into prolonged clotting times (PT and PTT). Since pre-term neonates have a high incidence of bleeding, particularly intraventricular hemorrhages, neonatologists frequently administer blood products (i.e., platelets and FFP) to non-bleeding neonates with low platelet counts or prolonged clotting times in an attempt to overcome these "deficiencies" and reduce bleeding risk. However, it has become increasingly clear that both the platelet hyporeactivity as well as the decreased coagulation factor levels are effectively counteracted by other factors in neonatal blood that promote hemostasis (i.e., high levels of vWF, high hematocrit and MCV, reduced levels of natural anticoagulants), resulting in a well-balanced neonatal hemostatic system, perhaps slightly tilted toward a prothrombotic phenotype. While life-saving in the presence of active major bleeding, the administration of platelets and/or FFP to non-bleeding neonates based on laboratory tests has not only failed to decrease bleeding, but has been associated with increased neonatal morbidity and mortality in the case of platelets. In this review, we will present a clinical overview of bleeding in neonates (incidence, sites, risk factors), followed by a description of the key developmental differences between neonates and adults in primary and secondary hemostasis. Next, we will review the clinical tests available for the evaluation of bleeding neonates and their limitations in the context of the developmentally unique neonatal hemostatic system, and will discuss current and emerging approaches to more accurately predict, evaluate and treat bleeding in neonates.

Thrombocytopenia in Neonates

Thrombocytopenia defined as platelet count below 150,000/μL is not an uncommon event at the neonatal intensive care unit (NICU). In our region we calculated a prevalence of nearly 2 of 1000 live births. Early-onset neonatal thrombocytopenia (NT) occurring within the first 72 hours of life is more common than late-onset NT. Preterm infants are affected more often than term infants and bacterial infection is the most common diagnosis associated with NT. There are a lot of maternal, perinatal, and neonatal causes associated with NT and complications include bleedings with potentially life-threatening intracranial hemorrhage. Alloimmune thrombocytopenia (NAIT) often presents with severe thrombocytopenia (<30,000/μL) in otherwise healthy newborns and needs careful evaluation regarding HPA-1a antigen status and HLA typing. Platelet transfusions are needed in severe NT and threshold platelet counts might be at ≤25,000/μL irrespective of bleeding or not. Immune mediated NT recovers within 2 weeks with a good prognosis when there happened no intracranial hemorrhage. This short review gives an overview on etiology and causes of NT and recommendations regarding platelet transfusions.

HIP (HPA-screening in pregnancy) study: protocol of a nationwide, prospective and observational study to assess incidence and natural history of fetal/neonatal alloimmune thrombocytopenia and identifying pregnancies at risk

INTRODUCTION

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) may lead to severe fetal or neonatal bleeding and/or perinatal death. Maternal alloantibodies, targeted against fetal human platelet antigens (HPAs), can result thrombocytopenia and bleeding complications. In pregnancies with known immunisation, fetal bleeding can be prevented by weekly maternal intravenous immunoglobulin infusions. Without population-based screening, immunisation is only detected after birth of an affected infant. Affected cases that might have been prevented, when timely identified through population-based screening. Implementation is hampered by the lack of knowledge on incidence, natural history and identification of pregnancies at high risk of bleeding. We designed a study aimed to obtain this missing knowledge.

METHODS AND ANALYSIS

The HIP (HPA-screening in pregnancy) study is a nationwide, prospective and observational cohort study aimed to assess incidence and natural history of FNAIT as well as identifying pregnancies at high risk for developing bleeding complications. For logistic reasons, we invite rhesus D-negative or rhesus c-negative pregnant women, who take part in the Dutch population-based prenatal screening programme for erythrocyte immunisation, to participate in our study. Serological HPA-1a typing is performed and a luminex-based multiplex assay will be performed for the detection of anti-HPA-1a antibodies. Results will not be communicated to patients or caregivers. Clinical data of HPA-1a negative women and an HPA-1a positive control group will be collected after birth. Samples of HPA-1a immunised pregnancies with and without signs of bleeding will be compared with identify parameters for identification of pregnancies at high risk for bleeding complications.

ETHICS AND DISSEMINATION

Ethical approval for this study has been obtained from the Medical Ethical Committee Leiden-The Hague-Delft (P16.002). Study enrolment began in March 2017. All pregnant women have to give informed consent for testing according to the protocol. Results of the study will be disseminated through congresses and publication in relevant peer-reviewed journals.

TRIAL REGISTRATION NUMBER

NCT04067375.

Epidemiology and management of fetal and neonatal alloimmune thrombocytopenia

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a disease in pregnancy characterized by maternal alloantibodies directed against the human platelet antigen (HPA). These antibodies can cause intracranial hemorrhage (ICH) or other major bleeding resulting in lifelong handicaps or death. Optimal fetal care can be provided by timely identification of pregnancies at risk. However, this can only be done by routinely antenatal screening. Whether nationwide screening is cost-effective is still being debated. HPA-1a alloantibodies are estimated to be found in 1 in 400 pregnancies resulting in severe burden and fetal ICH in 1 in 10.000 pregnancies. Antenatal treatment is focused on the prevention of fetal ICH and consists of weekly maternal IVIg administration. In high-risk FNAIT treatment should be initiated at 12-18 weeks gestational age using high dosage and in standard-risk FNAIT at 20-28 weeks gestational age using a lower dosage. Postnatal prophylactic platelet transfusions are often given in case of severe thrombocytopenia to prevent bleedings. The optimal threshold and product for postnatal transfusion is not known and international consensus is lacking. In this review practical guidelines for antenatal and postnatal management are offered to clinicians that face the challenge of reducing the risk of bleeding in fetuses and infants affected by FNAIT.

Fetal and neonatal alloimmune thrombocytopenia: recommendations for evidence-based practice, an international approach

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) may result in severe bleeding, particularly fetal and neonatal intracranial haemorrhage (ICH). As a result, FNAIT requires prompt identification and treatment; subsequent pregnancies need close surveillance and management. An international panel convened to develop evidence-based recommendations for diagnosis and management of FNAIT. A rigorous approach was used to search, review and develop recommendations from published data for: antenatal management, postnatal management, diagnostic testing and universal screening. To confirm FNAIT, fetal human platelet antigen (HPA) typing, using non-invasive methods if quality-assured, should be performed during pregnancy when the father is unknown, unavailable for testing or heterozygous for the implicated antigen. Women with a previous child with an ICH related to FNAIT should be offered intravenous immunoglobulin (IVIG) infusions during subsequent affected pregnancies as early as 12 weeks gestation. Ideally, HPA-selected platelets should be available at delivery for potentially affected infants and used to increase the neonatal platelet count as needed. If HPA-selected platelets are not immediately available, unselected platelets should be transfused. FNAIT studies that optimize antenatal and postnatal management, develop risk stratification algorithms to guide management and standardize laboratory testing to identify high risk pregnancies are needed.

Maternal HPA-1a antibody level and its role in predicting the severity of Fetal/Neonatal Alloimmune Thrombocytopenia: a systematic review

BACKGROUND AND OBJECTIVES

In Caucasians, fetal/neonatal alloimmune thrombocytopenia (FNAIT) is most commonly due to maternal HPA-1a antibodies. HPA-1a typing followed by screening for anti-HPA-1a antibodies in HPA-1bb women may identify first pregnancies at risk. Our goal was to review results from previous published studies to examine whether the maternal antibody level to HPA-1a could be used to identify high-risk pregnancies.

MATERIALS AND METHODS

The studies included were categorized by recruitment strategies: screening of unselected pregnancies or samples analyzed from known or suspected FNAIT patients.

RESULTS

Three prospective studies reported results from screening programmes, and 10 retrospective studies focused on suspected cases of FNAIT. In 8 studies samples for antibody measurement, performed by the monoclonal antibody immobilization of platelet antigen (MAIPA) assay, and samples for determining fetal/neonatal platelet count were collected simultaneously. In these 8 studies, the maternal antibody level correlated with the risk of severe thrombocytopenia. The prospective studies reported high negative predictive values (88-95%), which would allow for the use of maternal anti-HPA-1a antibody level as a predictive tool in a screening setting, in order to identify cases at low risk for FNAIT. However, due to low positive predictive values reported in prospective as well as retrospective studies (54-97%), the maternal antibody level is less suited for the final diagnosis and for guiding antenatal treatment.

CONCLUSION

HPA-1a antibody level has the potential to predict the severity of FNAIT.

Massive Fetomaternal Hemorrhage Remote from Term: Favorable Outcome after Fetal Resuscitation and Conservative Management

Fetomaternal hemorrhage (FMH) is a rare condition that requires early diagnosis and appropriate treatment due to its potentially severe consequences. We report a case of massive FMH presenting as decreased fetal movement, fetal hydrops, and intracranial hemorrhage at 24 weeks. Treatment considerations were made and amniocentesis, fetal blood sampling, and fetal blood transfusion via cordocentesis were performed. Recurrent FMH required subsequent fetal transfusion 2 days later. Surveillance was continued twice weekly until the patient delivered a viable infant at 38 weeks after spontaneous labor. Recurrent FMH was unpredictable due to its unclear etiology and absence of precipitating events, however close surveillance proved effective.

Maternal and foetal outcomes following natural vaginal versus caesarean section (c-section) delivery in women with bleeding disorders and carriers

BACKGROUND

Bleeding disorders are uncommon but may pose significant bleeding complications during pregnancy, labour and following delivery for both the woman and the foetus. While many bleeding disorders in women tend to improve in pregnancy, thus decreasing the haemorrhagic risk to the mother at the time of delivery, some do not correct or return quite quickly to their pre-pregnancy levels in the postpartum period. Therefore, specific measures to prevent maternal bleeding and foetal complications during childbirth, are required. The safest method of delivery to reduce morbidity and mortality in these women is controversial. This is an update of a previously published review.

OBJECTIVES

To assess the optimal mode of delivery in women with, or carriers of, bleeding disorders.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Coagulopathies Trials Register, compiled from electronic database searches and handsearching of journals and conference abstract books. We also searched the Cochrane Pregnancy and Childbirth Group's Trials Register as well as trials registries and the reference lists of relevant articles and reviews.Date of last search of the Group's Trials Registers: 16 February 2017.

SELECTION CRITERIA

Randomised controlled trials and all types of controlled clinical trials investigating the optimal mode of delivery in women with, or carriers of, any type of bleeding disorder during pregnancy were eligible for the review.

DATA COLLECTION AND ANALYSIS

No trials matching the selection criteria were eligible for inclusion MAIN RESULTS: No results from randomised controlled trials were found.

AUTHORS' CONCLUSIONS

The review did not identify any randomised controlled trials investigating the safest mode of delivery and associated maternal and foetal complications during delivery in women with, or carriers of, a bleeding disorder. In the absence of high quality evidence, clinicians need to use their clinical judgement and lower level evidence (e.g. from observational trials, case studies) to decide upon the optimal mode of delivery to ensure the safety of both mother and foetus.Given the ethical considerations, the rarity of the disorders and the low incidence of both maternal and foetal complications, future randomised controlled trials to find the optimal mode of delivery in this population are unlikely to be carried out. Other high quality controlled studies (such as risk allocation designs, sequential design, and parallel cohort design) are needed to investigate the risks and benefits of natural vaginal and caesarean section in this population or extrapolation from other clinical conditions that incur a haemorrhagic risk to the baby, such as platelet alloimmunisation.

Triplets with neonatal alloimmune thrombocytopenia due to antibodies against human platelet antigen 1a

BACKGROUND

Neonatal alloimmune thrombocytopenia (NAIT) has been reported only rarely in twins and not at all, to our knowledge, in triplets.

CASE REPORT

Nonidentical triplets were born with severe thrombocytopenia. Nadir platelet (PLT) counts were 17 × 10⁹ , 12 × 10⁹ , and 10 × 10⁹ /L. NAIT was confirmed by an incompatibility for human PLT antigen (HPA)-1a and the presence of maternal anti-HPA-1a. The maternal genotype was HPA-1bb and the paternal genotype was HPA-1aa; thus, all children were affected.

RESULTS

PLT counts for each infant improved with the administration of random-donor PLT transfusions. All three infants also received intravenous immunoglobulin. None had major bleeding. A small isolated subependymal hemorrhage was found incidentally in one infant; this remained stable on repeat imaging.

CONCLUSIONS

This is the first report of triplets with NAIT. Anti-HPA-1a is sufficiently potent to affect three infants simultaneously. Random-donor PLTs were effective in improving PLT counts in all three infants.

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.

Maternal and foetal outcomes following natural vaginal versus caesarean section (c-section) delivery in women with bleeding disorders and carriers

BACKGROUND

Bleeding disorders are uncommon but may pose significant bleeding complications during pregnancy, labour and following delivery for both the woman and the foetus. While many bleeding disorders in women tend to improve in pregnancy, thus decreasing the haemorrhagic risk to the mother at the time of delivery, some do not correct or return quite quickly to their pre-pregnancy levels in the postpartum period. Therefore, specific measures to prevent maternal bleeding and foetal complications during childbirth, are required. The safest method of delivery to reduce morbidity and mortality in these women is controversial.

OBJECTIVES

To assess the optimal mode of delivery in women with, or carriers of, bleeding disorders.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Coagulopathies Trials Register, compiled from electronic database searches and handsearching of journals and conference abstract books. We also searched the Cochrane Pregnancy and Childbirth Group's Trials Register as well as trials registries and the reference lists of relevant articles and reviews.Date of last search of the Group's Trials Registers: 13 January 2015.

SELECTION CRITERIA

Randomised controlled trials and all types of controlled clinical trials investigating the optimal mode of delivery in women with, or carriers of, any type of bleeding disorder during pregnancy were eligible for the review.

DATA COLLECTION AND ANALYSIS

No trials matching the selection criteria were eligible for inclusion

MAIN RESULTS

No results from randomized controlled trials were found.

AUTHORS' CONCLUSIONS

The review did not identify any randomised controlled trials investigating the safest mode of delivery and associated maternal and foetal complications during delivery in women with, or carriers of, a bleeding disorder. In the absence of high quality evidence, clinicians need to use their clinical judgement and lower level evidence (e.g. from observational trials, case studies) to decide upon the optimal mode of delivery to ensure the safety of both mother and foetus.Given the ethical considerations, the rarity of the disorders and the low incidence of both maternal and foetal complications, future randomised controlled trials to find the optimal mode of delivery in this population are unlikely to be carried out. Other high quality controlled studies (such as risk allocation designs, sequential design, and parallel cohort design) are needed to investigate the risks and benefits of natural vaginal and caesarean section in this population or extrapolation from other clinical conditions that incur a haemorrhagic risk to the baby, such as platelet alloimmunisation.

Human platelet antigen (HPA)-1a peptides do not reliably suppress anti-HPA-1a responses using a humanized severe combined immunodeficiency (SCID) mouse model

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) occurs most frequently when human platelet antigen (HPA)-1a-positive fetal platelets are destroyed by maternal HPA-1a immunoglobulin (Ig)G antibodies. Pregnancies at risk are treated by administration of high-dose intravenous Ig (IVIG) to women, but this is expensive and often not well tolerated. Peptide immunotherapy may be effective for ameliorating some allergic and autoimmune diseases. The HPA-1a/1b polymorphism is Leu/Pro33 on β3 integrin (CD61), and the anti-HPA-1a response is restricted to HPA-1b1b and HLA-DRB3*0101-positive pregnant women with an HPA-1a-positive fetus. We investigated whether or not HPA-1a antigen-specific peptides that formed the T cell epitope could reduce IgG anti-HPA-1a responses, using a mouse model we had developed previously. Peripheral blood mononuclear cells (PBMC) in blood donations from HPA-1a-immunized women were injected intraperitoneally (i.p.) into severe combined immunodeficient (SCID) mice with peptides and HPA-1a-positive platelets. Human anti-HPA-1a in murine plasma was quantitated at intervals up to 15 weeks. HPA-1a-specific T cells in PBMC were identified by proliferation assays. Using PBMC of three donors who had little T cell reactivity to HPA-1a peptides in vitro, stimulation of anti-HPA-1a responses by these peptides occurred in vivo. However, with a second donation from one of these women which, uniquely, had high HPA-1a-specific T cell proliferation in vitro, marked suppression of the anti-HPA-1a response by HPA-1a peptides occurred in vivo. HPA-1a peptide immunotherapy in this model depended upon reactivation of HPA-1a T cell responses in the donor. For FNAIT, we suggest that administration of antigen-specific peptides to pregnant women might cause either enhancement or reduction of pathogenic antibodies.

Neonatal alloimmune thrombocytopenia: pathogenesis, diagnosis and management

Neonatal alloimmune thrombocytopenia, (NAIT) is caused by maternal antibodies raised against alloantigens carried on fetal platelets. Although many cases are mild, NAIT is a significant cause of morbidity and mortality in newborns and is the most common cause of intracranial haemorrhage in full-term infants. In this report, we review the pathogenesis, clinical presentation, laboratory diagnosis and prenatal and post-natal management of NAIT and highlight areas of controversy that deserve the attention of clinical and laboratory investigators.

Crosstalk between Platelets and the Immune System: Old Systems with New Discoveries

Platelets are small anucleate cells circulating in the blood. It has been recognized for more than 100 years that platelet adhesion and aggregation at the site of vascular injury are critical events in hemostasis and thrombosis; however, recent studies demonstrated that, in addition to these classic roles, platelets also have important functions in inflammation and the immune response. Platelets contain many proinflammatory molecules and cytokines (e.g., P-selectin, CD40L, IL-1β, etc.), which support leukocyte trafficking, modulate immunoglobulin class switch, and germinal center formation. Platelets express several functional Toll-like receptors (TLRs), such as TLR-2, TLR-4, and TLR-9, which may potentially link innate immunity with thrombosis. Interestingly, platelets also contain multiple anti-inflammatory molecules and cytokines (e.g., transforming growth factor-β and thrombospondin-1). Emerging evidence also suggests that platelets are involved in lymphatic vessel development by directly interacting with lymphatic endothelial cells through C-type lectin-like receptor 2. Besides the active contributions of platelets to the immune system, platelets are passively targeted in several immune-mediated diseases, such as autoimmune thrombocytopenia, infection-associated thrombocytopenia, and fetal and neonatal alloimmune thrombocytopenia. These data suggest that platelets are important immune cells and may contribute to innate and adaptive immunity under both physiological and pathological conditions.

Review of neonatal alloimmune thrombocytopenia

Neonatal alloimmune thrombocytopenia (NAIT), with an incidence of one in 1000 live births, is the most common cause of severe thrombocytopenia and intra-cerebral haemorrhage in term neonates. NAIT results from trans-placental passage of maternal antibodies against a paternally derived fetal platelet alloantigen. Clinical presentation varies from unexpected thrombocytopenia on a blood film in a well newborn to intracranial haemorrhage (ICH). In contrast to haemolytic disease of the newborn, NAIT can present in a first pregnancy, and subsequent pregnancies are usually more severely affected. The role of antenatal screening for maternal alloantibodies instead of fetal blood sampling to identify at-risk fetuses remains uncertain, but there is a trend towards less invasive maternally directed treatment for at-risk pregnancies. Neonatal management is aimed at preventing or limiting thrombocytopenic bleeding with transfusion of antigen-matched platelets.

The maternal immune response to fetal platelet GPIbα causes frequent miscarriage in mice that can be prevented by intravenous IgG and anti-FcRn therapies

Fetal and neonatal immune thrombocytopenia (FNIT) is a severe bleeding disorder caused by maternal antibody-mediated destruction of fetal/neonatal platelets. It is the most common cause of severe thrombocytopenia in neonates, but the frequency of FNIT-related miscarriage is unknown, and the mechanism(s) underlying fetal mortality have not been explored. Furthermore, although platelet αIIbβ3 integrin and GPIbα are the major antibody targets in immune thrombocytopenia, the reported incidence of anti-GPIbα-mediated FNIT is rare. Here, we developed mouse models of FNIT mediated by antibodies specific for GPIbα and β3 integrin and compared their pathogenesis. We found, unexpectedly, that miscarriage occurred in the majority of pregnancies in our model of anti-GPIbα-mediated FNIT, which was far more frequent than in anti-β3-mediated FNIT. Dams with anti-GPIbα antibodies exhibited extensive fibrin deposition and apoptosis/necrosis in their placentas, which severely impaired placental function. Furthermore, anti-GPIbα (but not anti-β3) antiserum activated platelets and enhanced fibrin formation in vitro and thrombus formation in vivo. Importantly, treatment with either intravenous IgG or a monoclonal antibody specific for the neonatal Fc receptor efficiently prevented anti-GPIbα-mediated FNIT. Thus, the maternal immune response to fetal GPIbα causes what we believe to be a previously unidentified, nonclassical FNIT (i.e., spontaneous miscarriage but not neonatal bleeding) in mice. These results suggest that a similar pathology may have masked the severity and frequency of human anti-GPIbα-mediated FNIT, but also point to possible therapeutic interventions.

Antenatal interventions for fetomaternal alloimmune thrombocytopenia

BACKGROUND

Fetomaternal alloimmune thrombocytopenia results from the formation of antibodies by the mother which are directed against a fetal platelet alloantigen inherited from the father. The resulting fetal thrombocytopenia (reduced platelet numbers) may cause bleeding, particularly into the brain, before or shortly after birth. Antenatal treatment of fetomaternal alloimmune thrombocytopenia includes the administration of intravenous immunoglobulin (IVIG) and/or corticosteroids to the mother to prevent severe fetal thrombocytopenia. IVIG and corticosteroids both have short-term and possibly long-term side effects. IVIG is also costly and optimal regimens need to be identified.

OBJECTIVES

To determine the optimal antenatal treatment of fetomaternal alloimmune thrombocytopenia to prevent fetal and neonatal haemorrhage and death.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (28 February 2011) and bibliographies of relevant publications and review articles.

SELECTION CRITERIA

Randomised controlled studies comparing any intervention with no treatment, or comparing any two interventions.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed eligibility, trial quality and extracted data.

MAIN RESULTS

We included four trials involving 206 people. One trial involving 39 people compared a corticosteroid (prednisone) versus IVIG alone. In this trial, where analysable data were available, there was no statistically significant differences between the treatment arms for predefined outcomes. Three trials involving 167 people compared IVIG plus a corticosteroid (prednisone in two trials and dexamethasone in one trial) versus IVIG alone. In these trials there was no statistically significant difference in the findings between the treatment arms for predefined outcomes (intracranial haemorrhage; platelet count at birth and preterm birth). Lack of complete data sets and important differences in interventions precluded the pooling of data from these trials.

AUTHORS' CONCLUSIONS

The optimal management of fetomaternal alloimmune thrombocytopenia remains unclear. Lack of complete data sets for two trials and differences in interventions precluded the pooling of data from these trials which may have enabled a more developed analysis of the trial findings. Further trials would be required to determine optimal treatment (the specific medication and its dose and schedule). Such studies should include long-term follow up of all children and mothers.

A review of pathophysiology and current treatment for neonatal alloimmune thrombocytopenia (NAIT) and introducing the Australian NAIT registry

Fetomaternal or neonatal alloimmune thrombocytopenia (NAIT) is a rare but serious condition associated with significant fetal and neonatal morbidity and mortality. The most useful predictor of severe disease is a history of a sibling with an antenatal intracranial haemorrhage. However, NAIT can occur during the first pregnancy and may not be diagnosed until the neonatal period. Antenatal treatment options include maternal intravenous immunoglobulin (IVIG) and corticosteroid treatment, fetal blood sampling (FBS) and intrauterine platelet transfusion (IUT) and early delivery. FBS (with or without IUT) can be used to direct and monitor response to therapy, and to inform mode and timing of delivery. However, this procedure is associated with significant risks, including fetal death, and is generally now reserved for high-risk pregnancies. This review highlights the current understanding of the epidemiology and pathophysiology of NAIT and summarises current approaches to investigation and management. It also introduces the newly established Australian NAIT registry. Owing to the relative rarity of NAIT, accruing sufficient patient numbers for studies and clinical trials at an institutional level is difficult. This national registry will provide an opportunity to collect valuable information and inform future research on this condition.

New low-frequency platelet glycoprotein polymorphisms associated with neonatal alloimmune thrombocytopenia

BACKGROUND

Recent reports suggest that maternal immunization against low-frequency, platelet (PLT)-specific glycoprotein (GP) polymorphisms is a more common cause of neonatal alloimmune thrombocytopenia (NATP) than previously thought.

STUDY DESIGN AND METHODS

Serologic and molecular studies were performed on PLTs and DNA from three families in which an infant was born with apparent NATP not attributable to maternal immunization against known PLT-specific alloantigens.

RESULTS

Antibodies reactive only with paternal PLTs were identified in each mother. In Cases 2 (Kno) and 3 (Nos), but not Case 1 (Sta), antibody recognized paternal GPIIb/IIIa in solid-phase assays. Unique mutations encoding amino acid substitutions in GPIIb (Case 2) or GPIIIa (Cases 1 and 3) were identified in paternal DNA and in DNA from two of the affected infants. Antibody from all three cases recognized recombinant GPIIIa (Case 1 [Sta] and Case 3 [Nos]) and GPIIb (Case 2, Kno) mutated to contain the polymorphisms identified in the respective fathers. None of 100 unselected normal subjects possessed the paternal mutations. Enzyme-linked immunosorbent assay and flow cytometric studies suggested that failure of maternal serum from Case 1 (Sta) to react with paternal GPIIIa in solid-phase assays resulted from use of a monoclonal antibody AP2, for antigen immobilization that competed with the maternal antibody for binding to the Sta epitope.

CONCLUSION

NATP in the three cases was caused by maternal immunization against previously unreported, low-frequency GP polymorphisms. Maternal immunization against low-frequency PLT-specific alloantigens should be considered in cases of apparent NATP not resolved by conventional serologic and molecular testing.

Management of fetal alloimmune thrombocytopenia-a less invasive option?

Fetal alloimmune thrombocytopenia (FAITP) is a condition associated with significant infant morbidity and mortality. We report on the West of Scotland experience of 30 pregnancies complicated by FAITP over a 17-year period (1982-98). Management options included serial cordocentesis together with platelet transfusion, and maternal intravenous gammaglobulin (IVIgG) therapy. Of those pregnancies managed by serial cordocentesis all had poor outcomes. Weekly IVIgG was administered to the remaining pregnancies, all of which had a good outcome although four infants were thrombocytopenic at birth. None of these cases had previously been complicated by intracranial haemorrhage. In the milder end of the spectrum of FAITP we would suggest that IVIgG is an alternative treatment option.

Diagnosis and management of the fetus and neonate with alloimmune thrombocytopenia

Fetal and neonatal alloimmune thrombocytopenia (AIT) is the commonest cause of severe thrombocytopenia in neonates, and of intracranial hemorrhage (ICH) in term neonates [1] (J Trop Pediatr, 1999; 45: 237). If a newborn is affected with AIT, the next child will likely be more severely affected, and therefore fetal thrombocytopenia will begin early in gestation [2, 3] (Arch Neurol, 1984; 41: 30; N Engl J Med 1997; 337: 22). This creates a risk of in utero ICH even if there was not one in the previous pregnancy. There are new developments in AIT in regard to diagnosis, treatment, and screening which will be the focus of this review.

Current approaches to the evaluation and management of the fetus and neonate with immune thrombocytopenia

Fetal and neonatal alloimmune thrombocytopenia is not a well-known disease, except among specialists in maternal-fetal medicine, neonatologists, and certain pediatricians (ie, hematologists). However, this is by far the most common cause of early severe thrombocytopenia in neonates and of intracranial hemorrhage in term neonates. In addition, if a newborn is affected with alloimmune thrombocytopenia, the next child in the family will likely be more severely affected. Thus, the accurate diagnosis and appropriate management of this disorder are of extreme importance in perinatal medicine and will constitute the focus of this review.

Fetal thrombocytopenia

Fetal thrombocytopenia is most often caused by maternal alloantibodies against fetal platelets crossing the placenta and resulting in platelet destruction. This condition, known as fetal and neonatal alloimmune thrombocytopenia, is usually detected after the birth of a symptomatic child who shows signs of bleeding in the skin or in the brain. In the most severe cases, intracranial hemorrhage leads to severe handicap or death. The challenge for the clinician is to provide preventive treatment in the next pregnancy. The current cornerstone of this treatment is maternal intravenous administration of immunoglobulins during the second half of pregnancy.

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.

A screening and intervention program aimed to reduce mortality and serious morbidity associated with severe neonatal alloimmune thrombocytopenia

The study's objective was to identify HPA 1a-negative women and to offer them an intervention program aimed to reduce morbidity and mortality of neonatal alloimmune thrombocytopenia (NAIT). HPA 1 typing was performed in 100 448 pregnant women. The HPA 1a-negative women were screened for anti-HPA 1a. In immunized women, delivery was performed by Cesarean section 2 to 4 weeks prior to term, with platelets from HPA 1a-negative donors reserved for immediate transfusion if petechiae were present and/or if platelet count was less than 35 x 10(9)/L. Of the women screened, 2.1% were HPA 1a negative, and anti-HPA 1a was detected in 10.6% of these. One hundred seventy pregnancies were managed according to the intervention program, resulting in 161 HPA 1a-positive children. Of these, 55 had severe thrombocytopenia (< 50 x 10(9)/L), including 2 with intracranial hemorrhage (ICH). One woman with a twin pregnancy missed the follow-up and had one stillborn and one severely thrombocytopenic live child. In 15 previous prospective studies (136 814 women) there were 51 cases of severe NAIT (3 intrauterine deaths and 7 with ICH). Acknowledging the limitation of comparing with historic controls, implementation of our screening and intervention program seemed to reduce the number of cases of severe NAIT-related complications from 10 of 51 to 3 of 57.

Noninvasive antenatal management of fetal and neonatal alloimmune thrombocytopenia: safe and effective

OBJECTIVE

To describe the outcome of pregnancies with fetal and neonatal alloimmune thrombocytopenia (FNAIT) in relation to the invasiveness of the management protocol.

DESIGN

Retrospective analysis of prospectively collected data from a national cohort.

SETTING

Leiden University Medical Centre, the national centre for management of severe red cell and platelet alloimmunisation in pregnancy.

POPULATION

Ninety-eight pregnancies in 85 women with FNAIT having a previous child with thrombocytopenia with (n= 16) or without (n= 82) an intracranial haemorrhage (ICH).

METHODS

Our management protocol evolved over time from (1) serial fetal blood samplings (FBS) and platelet transfusion (n= 13) via (2) combined FBS with maternal intravenous immunoglobulins (n= 33) to (3) completely noninvasive treatment with immunoglobulins only (n= 52 pregnancies, resulting in 53 neonates). Perinatal outcome was assessed according to the three types of management.

MAIN OUTCOME MEASURES

Occurrence of ICH, perinatal survival, gestational age at birth and complications of FBS.

RESULTS

All but one of 98 pregnancies ended in a live birth; none of the neonates had an ICH. The median gestational age at birth was 37 weeks (range 32-40). In groups 1 and 2, three emergency caesarean sections were performed after complicated FBS, resulting in two healthy babies and one neonatal death.

CONCLUSION

Noninvasive antenatal management of pregnancies complicated by FNAIT appears to be both effective and safe.

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.

Antenatal noninvasive treatment of patients at risk for alloimmune thrombocytopenia without a history of intracranial hemorrhage

OBJECTIVE

The purpose of this study was to evaluate noninvasive management of alloimmune thrombocytopenia that included only the blind administration of immunoglobulin.

STUDY DESIGN

Seventeen women with 30 pregnancies that were at risk of neonatal alloimmune thrombocytopenia were included. Except for 6 cases, in which the women refused treatment, 24 pregnancies were managed by the weekly administration of intravenous immunoglobulin without monitoring platelet count.

RESULTS

The mean platelet count at birth after intravenous immunoglobulin treatment was 118,000/microL, compared with 25,000/microL among the 17 first affected infants and 24,000/microL among the 6 infants whose mothers refused treatment (P < .05). Only 8% of the treated fetuses had platelet counts of <30,000/microL at birth, compared with 70% of the untreated infants (P < .05). None of the treated and nontreated fetuses had an intracranial hemorrhage.

CONCLUSION

Noninvasive management of alloimmune thrombocytopenia that consists of only immunoglobulin administration is highly effective and seems safe in women without a history of fetal/neonatal intracranial hemorrhage.

Prospective epidemiologic study of the outcome and cost-effectiveness of antenatal screening to detect neonatal alloimmune thrombocytopenia due to anti-HPA-1a

BACKGROUND

To assess the value of antenatal screening to detect neonatal alloimmune thrombocytopenia (NAIT) due to anti-HPA-1a, a prospective study was carried out to quantify the potential clinical benefits and determine whether screening would be cost-effective.

STUDY DESIGN AND METHODS

An observational prospective controlled study was carried out on 26,506 pregnant women over 2 years. HPA-1a phenotyping was performed in the first trimester and women confirmed HPA-1a-negative were tested for anti-HPA-1a during pregnancy, at delivery, and 10 to 14 days after birth. Babies of HPA-1a-negative women were tested at delivery for thrombocytopenia and examined for signs of bleeding. Economic evaluation was undertaken on the basis of the data collected during the study.

RESULTS

Twenty-five of 318 women (7.9%) had anti-HPA-1a detected for the first time. Eight women (43 per 100,000) gave birth to babies with NAIT, and 5 (27 per 100,000) had severe thrombocytopenia. Three babies had mild signs of bleeding, and no cases of intracranial hemorrhage (ICH) or fetal loss were detected. It is estimated that it would cost 60,596 pounds (98,771 US dollars) to detect a case of severe NAIT, where anti-HPA-1a has been identified for the first time, and 1,151,323 pounds (1,876,656 US dollars) to prevent a case of ICH, assuming that detection allowed successful intervention.

CONCLUSIONS

Our data suggest that severe HPA-1a NAIT is underdiagnosed in the absence of routine antenatal screening. Serious bleeding complications and ICH, however, occur less frequently in first cases of NAIT than suspected from the literature, and the costs of screening and possible intervention must be balanced against the procedural risks.

Intravenous Immunoglobulins without Initial and Follow-Up Cordocentesis in Alloimmune Fetal and Neonatal Thrombocytopenia at High Risk for Intracranial Hemorrhage

OBJECTIVE

To report on a less invasive treatment strategy in alloimmune fetal and neonatal thrombocytopenia (FNAIT) at high risk for either in utero or neonatal intracranial hemorrhage (ICH).

METHODS

In 7 pregnancies, with a history of ICH in the older sibling, weekly intravenous immunoglobulin (IVIG) therapy to the mother (1 g/kg) without initial cordocentesis was started at a median gestational age of 16 weeks.

RESULTS

In 4 pregnancies cordocentesis was avoided. One predelivery cordocentesis with platelet transfusion was performed in 3 further cases. Although none of the cases had a platelet count of >50 x 10(9)/l at cordocentesis, predelivery or birth, no ICHs were observed. The neonatal periods of the infants were uncomplicated.

CONCLUSION

IVIG treatment alone might be considered in patients with both severe platelet alloimmunization and an increased risk for morbidity and mortality at cordocentesis.

Maternal alloimmunization against the rare platelet-specific antigen HPA-9b (Max a) is an important cause of neonatal alloimmune thrombocytopenia

BACKGROUND

Neonatal alloimmune thrombocytopenia (NATP) is an important cause of morbidity and mortality in the newborn. Optimal management of subsequent pregnancies requires knowledge of the alloantigen that caused maternal immunization, but this is possible only in a minority of cases. This study investigated whether this can be explained in part by maternal immunization against the "rare" alloantigen HPA-9b (Max(a)), implicated previously only in a single NATP case.

STUDY DESIGN AND METHODS

Archived paternal DNA from unresolved cases of NATP and normal individuals was typed for platelet (PLT)-specific antigens with real-time polymerase chain reaction and direct sequencing. PLT-specific alloantibodies were characterized by flow cytometry and solid-phase enzyme-linked immunosorbent assay. Recombinant GPIIb/IIIa was expressed in stably transfected Chinese hamster ovary cells. Clinical information was obtained directly from attending physicians.

RESULTS

Six of 217 fathers were positive for the presence of HPA-9b (Max(a)), an incidence about seven times that in the general population. In each of five cases studied, maternal serum samples reacted with intact paternal PLTs and paternal GPIIb/IIIa. Only one of three serum samples tested recognized recombinant GPIIb/IIIa carrying the HPA-9b (Max(a)) mutation. These seemingly discrepant reactions may reflect different requirements for oligosaccharides linked to residues close to the mutation in GPIIb that determines HPA-9b (Max(a)). NATP in the affected children was severe and was associated with intracranial hemorrhage in three of six infants on whom information was obtained.

CONCLUSIONS

Maternal immunization against HPA-9b (Max(a)) is an important cause of NATP and should be considered in cases of apparent NATP not resolved on the basis of maternal-fetal incompatibility for "common" PLT antigens.

Clinical and diagnostic comparison of neonatal alloimmune thrombocytopenia to non-immune cases of thrombocytopenia

BACKGROUND

Affected patients with neonatal alloimmune thrombocytopenia (AIT) are often severely thrombocytopenic and, if so, may suffer an intracranial hemorrhage (ICH). This study was undertaken to compare the outcome of cases of AIT to cases of neonatal thrombocytopenia shown not to be AIT and to identify clinical features that would facilitate the diagnosis.

PROCEDURE

Two hundred twenty two cases of neonatal thrombocytopenia for which serologic testing was obtained by the referring physician were accrued for this study from 11 testing laboratories. The relevant clinical information was pursued.

RESULTS

The mean birth platelet count in 110 neonates with AIT was 26,000/mm(3) x 10(9)/L and the rate of ICH was 11% (not all neonates had head sonos). Three criteria distinguished cases of AIT from other causes of neonatal thrombocytopenia (n = 56): (1) severe thrombocytopenia <50,000/mm(3) x 10(9)/L; (2) ICH associated with 1 or more of: a 1-min Apgar score >5, birthweight >2,200 g, grade >1, antenatal occurrence, or signs of bleeding, that is, petechiae, ecchymoses; and (3) no additional, non-hemorrhagic neonatal medical problems.

CONCLUSIONS

AIT is a unique type of neonatal thrombocytopenia with significant hemorrhagic consequences. Identification of AIT at the bedside should guide institution of appropriate treatment and lead to serologic testing for confirmation.

Frequency distribution of human platelet antigens in the Indian population

This study was undertaken with an aim of establishing the frequency distribution of various human platelet antigens (HPA) in Indian populations by means of DNA-based technology. A total of 1164 people belonging to various population groups were studied for the frequency distribution of HPA. DNA extraction was performed from peripheral venous blood samples. Polymerase chain reaction allele-specific amplification technique was used for HPA genotyping. The HPA bands were visualized by using ethidium bromide-stained agarose gel, after electrophoresis. The homozygosity of the HPA-1b/1b genotype was found to be significantly higher (P < 0.05) in the Parsi population group and Vatalia Prajapati population group, compared to Maharashtrians. Frequency distribution of HPA-1b in our populations was found to be slightly lower than that reported in some western populations. This study has established a DNA technique to diagnose cases of NAITP definitively and to treat these cases during the neonatal period, and also gives the frequency distribution of HPA in some of the Indian population.

Antenatal interventions for fetomaternal alloimmune thrombocytopenia

BACKGROUND

Fetomaternal alloimmune thrombocytopenia occurs when the mother produces antibodies against a platelet alloantigen that the fetus has inherited from the father. A consequence of this can be a reduced number of platelets (thrombocytopenia) in the fetus, which can result in bleeding whilst in the womb or shortly after birth. In severe cases this bleeding may lead to long-lasting disability or death. Antenatal management of fetomaternal alloimmune thrombocytopenia centres on preventing severe thrombocytopenia in the fetus. Available management options include administration of intravenous immunoglobulins or corticosteroids to the mother or intrauterine transfusion of antigen compatible platelets to the fetus. All options are costly and need to be assessed in terms of potential risk and benefit to both the mother and an individual fetus.

OBJECTIVES

To determine the optimal antenatal treatment of fetomaternal alloimmune thrombocytopenia to prevent fetal and neonatal haemorrhage and death.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group trials register (February 2004), EMBASE (1980 to February 2004) and bibliographies of relevant publications and review articles.

SELECTION CRITERIA

Randomised controlled studies comparing any intervention, including corticosteroids with no treatment, or comparing any two interventions.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed eligibility, trial quality and extracted data.

MAIN RESULTS

One study met the inclusion criteria (54 pregnant women). This trial compared intravenous immunoglobulins plus corticosteroid (dexamethasone) with intravenous immunoglobulins alone. No significant differences were reported between the treatment and control groups, in any outcome measured: mean platelet count at birth (weighted mean difference (WMD) 14.10 x 10 9/l, 95% confidence interval (CI) -30.26 to 58.46), mean gestational age at birth (WMD -0.50 weeks, 95% CI -2.69 to 1.69), mean rise in platelet count from first to second fetal blood screen (WMD -3.50 x 10 9/l, 95% CI -24.62 to 17.62) and mean rise in platelet count from birth to first fetal blood screen (WMD 24.40 x 10 9/l (95% CI -14.17 to 62.97)). This trial had adequate methodological quality; however the method used to calculate sample size was inappropriate: therefore the power calculation was not sufficient to determine any significance in differences between the treatment groups.

AUTHORS' CONCLUSIONS

There are insufficient data from randomised controlled trials to determine the optimal antenatal management of fetomaternal alloimmune thrombocytopenia. Future trials should consider the dose of intravenous immunoglobulins, the timing of initial treatment, monitoring of response to treatment by fetal blood sampling, laboratory measures to define pregnancies with a high risk of intercranial haemorrhage, management of non-responders and long-term follow up of children.

The natural history of maternal immunization against foetal platelet alloantigens

Foetomaternal alloimmune thrombocytopenia (FMAIT) occurs when maternal antibodies of an antigen-negative mother cause destruction of sensitized foetal platelets. In Caucasian populations, 6-12% of human platelet antigen (HPA)-1a-negative women develop anti-HPA-1a, and the incidence of clinically affected cases is estimated to be 10-20% of immunized women. This study was performed in order to elucidate the rate of maternal immunization, incidence of FMAIT and the likely outcome of the condition in Asians. Excluding two or more pregnancies during the period, serum samples from 24 630 pregnant women, mainly Japanese, were screened for antibodies against platelet alloantigens by means of mixed passive haemagglutination (MPHA) (Anti-HPA-MPHA, Olympus, Tokyo). Antibodies were detected in 0.91% (223/24 630) of the women's samples and the immunization rate was correlated with the number of pregnancies. Antibody specificity included anti-HPA-4b (49), anti-HPA-5a (three), anti-HPA-5b (168), anti-HPA-4b + 5b (one) and anti-Nak(a) (CD36) (two). No alloimmunization was observed within the HPA-1, HPA-2, HPA-3 or HPA-6 systems. Among HPA-4b- or HPA-5b-negative women, 24% or 14% estimated, respectively, had antibodies and 26% (10/38) or 10% (12/125) of neonates, respectively, born to these mothers developed thrombocytopenia. Two neonates born to mothers having anti-HPA-4b developed generalized purpura. No cases of intracranial bleeding or death due to FMAIT were recorded. Generalized purpura due to FMAIT occurs in one in 9359 (95% CI: 1 in 77 519-1 in 2591) pregnancies solely because of HPA-4b incompatibility.