Antenatal immunoglobulin for fetal red blood cell alloimmunization

  • Review
  • Intervention

Authors


Abstract

Background

Red blood cell alloimmunization in pregnancy can lead to fetal anaemia with potentially disastrous consequences. Traditional management involves the use of intrauterine transfusion, which is associated with significant procedure-related risks. An alternative treatment that has been trialled is the use of immunoglobulin administered intravenously to the mother.

Objectives

The objective of this review was to assess the efficacy and safety of the use of intravenous immunoglobulin antenatally to women with severe fetal red blood cell alloimmunization.

Search methods

We searched the Cochrane Pregnancy and Childbirth Group trials register (19 December 2012), and reference lists of articles.

Selection criteria

Randomized trials assessing the antenatal use of intravenous immunoglobulin administered at any dose, frequency or duration with a control group (using any other, or no treatment) in the management of fetal red blood cell alloimmunization.

Data collection and analysis

Two review authors independently assessed the available evidence.

Main results

There are no included studies.

Authors' conclusions

No information is available from randomized trials to indicate whether the antenatal use of intravenous immunoglobulin is effective in the management of fetal red blood cell alloimmunization. Several case series suggest a beneficial role in delaying the onset of fetal anaemia requiring invasive intrauterine transfusion.

Résumé scientifique

L'immunoglobuline prénatale pour l'allo-immunisation des globules rouges fœtaux

Contexte

L'allo-immunisation des globules rouges pendant la grossesse peut entraîner une anémie fœtale avec des conséquences potentiellement désastreuses. La prise en charge traditionnelle implique l'utilisation de la procédure de transfusion intra-utérine qui est associée à des risques importants. Un traitement alternatif, l'administration intraveineuse d'immunoglobuline à la mère, a été essayé.

Objectifs

L'objectif de cette revue était d'évaluer l'efficacité et l'innocuité de l'administration intraveineuse d'immunoglobuline pendant la période prénatale aux femmes avec allo-immunisation grave des globules rouges du fœtus.

Stratégie de recherche documentaire

Nous avons effectué des recherches dans le registre d'essais du groupe Cochrane sur la grossesse et l'accouchement (le 19 décembre 2009) et dans les références bibliographiques d'articles.

Critères de sélection

Des essais randomisés évaluant l'administration prénatale d'immunoglobuline par voie intraveineuse, quelles que soient la dose, la fréquence ou la durée, en comparaison avec un groupe de contrôle (autre traitement ou absence de traitement), dans la prise en charge de l'allo-immunisation des globules rouges fœtaux.

Recueil et analyse des données

Deux auteurs de la revue ont évalué les données disponibles de façon indépendante.

Résultats principaux

Il n'y a pas d'études incluses.

Conclusions des auteurs

On ne dispose pas d'informations issues d'essais randomisés indiquant si l'administration intraveineuse prénatale d'immunoglobuline est efficace dans la prise en charge de l'allo-immunisation des globules rouges fœtaux. Plusieurs séries de cas laissent apparaitre un rôle bénéfique par l'apparition retardée de l'anémie fœtale nécessitant une transfusion intra-utérine invasive.

Plain language summary

Antenatal immunoglobulin for fetal red blood cell alloimmunization

Pregnant women may develop antibodies in response to antigens on fetal red blood cells. The antibodies that result can cross the placenta to the fetus and break down red blood cells, leading to fetal anaemia. This has become less common with the routine use of anti D immunoglobulin in pregnant women with a Rhesus D-negative blood group and no pre-existing anti-D antibodies, but remains a cause of fetal death. Currently, standard management involves monitoring antibody titres in conjunction with ultrasound assessment of fetal well-being, and the use of intrauterine transfusion when fetal anaemia is diagnosed. Unfortunately, intrauterine transfusion poses significant risks because of its inherent invasiveness and procedure-related risks, including a risk of perinatal death.

Intravenous immunoglobulin has been proposed as an alternative form of treatment, with the advantage of being less invasive. There are no randomized trials of intravenous immunoglobulin given antenatally to women with severe fetal red blood cell alloimmunization to show if this offers any benefit over other forms of treatment or no treatment, but there are case series suggesting a possible role in delaying the onset of fetal anaemia requiring invasive intrauterine transfusion.

Résumé simplifié

L'immunoglobuline prénatale pour l'allo-immunisation des globules rouges du fœtus

Les femmes enceintes sont susceptibles de développer des anticorps en réponse à des antigènes sur les globules rouges du fœtus. Ces anticorps peuvent traverser le placenta et détruire les globules rouges du fœtus, entraînant une anémie fœtale. Cela est devenu moins fréquent avec l'utilisation systématique de l'immunoglobuline anti-D chez les femmes enceintes de Rhésus D négatif et sans anticorps anti-D pré-existants, mais cela reste une cause de mort du fœtus. Actuellement, la prise en charge standard consiste à surveiller les titres d'anticorps en conjonction avec l'évaluation échographique du bien-être fœtal, et à recourir à la transfusion intra-utérine lorsqu'une anémie fœtale est diagnostiquée. Malheureusement, la transfusion intra-utérine présente des risques importants en raison de son caractère envahissant inhérent et de risques liés à la procédure, y compris le risque de mort périnatale.

L'immunoglobuline intraveineuse a été proposée comme alternative moins invasive de traitement. Il n'y a pas d'essais randomisés sur l'immunoglobuline intraveineuse administrée pendant la période prénatale aux femmes avec allo-immunisation grave des globules rouges du fœtus qui permettent de voir si cela présente un avantage par rapport aux autres formes de traitement ou à l'absence de traitement, mais il y a des séries de cas suggérant que cela pourrait retarder l'apparition de l'anémie fœtale nécessitant une transfusion intra-utérine invasive.

Notes de traduction

Traduit par: French Cochrane Centre 3rd June, 2013
Traduction financée par: Pour la France : Minist�re de la Sant�. Pour le Canada : Instituts de recherche en sant� du Canada, minist�re de la Sant� du Qu�bec, Fonds de recherche de Qu�bec-Sant� et Institut national d'excellence en sant� et en services sociaux.

Background

Antigens on the red blood cell (erythrocyte) include the Rhesus antigens D, C, c, E, and e, as well as less common antigens such as Kell, MNS, and P antigens. Red blood cell alloimmunization has become less common with the routine use of anti D immunoglobulin during pregnancy and after delivery, but it may still occur with either D or non-D red blood cell antigens. Maternal antibodies may develop as a result of exposure to foreign red blood cell antigens via mechanisms including blood transfusion and transplacental fetomaternal haemorrhage. Since many of the red blood cell antigens are expressed on the fetal erythrocyte by the end of the first trimester, these maternal antibodies can cross the placenta. If they activate fetal red blood cell destruction (or, in the case of Kell antibodies, additionally suppress erythropoiesis), fetal anaemia can result, ultimately leading to hydrops or death, or both.

Traditionally, management of pregnant women demonstrating these antibodies has involved monitoring their antibody titres. In the past, once a titre reached a critical level, further evaluation via amniotic fluid bilirubin levels as an indirect measure of fetal haemolysis would be performed. Such evaluation is generally deemed mandatory when titres reach 32, as these levels correlate with a possibility of severe fetal anaemia in all antibody cases except Kell-alloimmunization. In the case of Kell-alloimmunization, antibodies not only activate fetal haemolysis, but also act independently to suppress erythropoiesis at the progenitor cell level, making the critical titre difficult to estimate (van Wamelen 2007). In the last decade, diagnosis of fetal anaemia via Doppler assessment of the fetal middle cerebral artery (MCA) peak systolic velocity has revolutionized practice in many centres, eliminating the need for amniotic fluid evaluation and thus rendering the management of alloimmunization far less invasive (Mari 2000; Oepkes 2006).

Despite the almost universal use of Doppler ultrasound in the evaluation of fetal red cell alloimmunization, the invasive requirement of the established therapy of choice, intrauterine transfusion (IUT), remains. Whilst experience in this field has improved greatly, complication rates are still impressive, with procedure-related perinatal mortality rates of up to 5% (van Kamp 2005).

Alternative treatment modalities have been proposed and trialled. These include plasmapheresis, oral erythrocyte membrane therapy, various medical agents such as azathioprine, promethazine and prednisolone, and intravenous immunoglobulin (IVIG) (Odendaal 1986; Ruma 2007). The latter has been used successfully in haematological and other obstetric settings, most notably and analogously in the area of platelet alloimmunization (Clark 1999; Rayment 2005). IVIG use was reported in isolated cases of red blood cell alloimmunization in the 1980s (e.g. Berlin 1985), and only began to be trialled more extensively in case series from 1990 onward (Chitkara 1990). As a proposed alternative treatment to IUT, IVIG is particularly attractive in the management of women with a history of severe alloimmunization in previous pregnancies. These women are at risk of alloimmunization and consequent fetal anaemia early in their subsequent pregnancy, when the technical difficulty and potential morbidity associated with IUT is at its highest. The use of IVIG instead of IUT, or to enable a delay in IUT, also reduces the risk of iatrogenic induction of maternal red cell alloimmunization (Watson 2006).

IVIG has proved safe in many applications, but is not free from adverse effects. Transmission of blood-borne diseases is now rare in most centres due to rigorous infectious control measures, but other serious reactions remain a real, if rare possibility. These include severe headaches, renal dysfunction, and maternal cardiovascular compromise (Cantu 1995; Duhem 1994).

There have been no randomized controlled trials comparing the use of IVIG either compared with no treatment or other treatments for fetal red blood cell alloimmunization. There have been 11 case series since 1990, with the majority (eight) examining the maternal administration of IVIG rather than fetal administration (Chitkara 1990; Connan 2009; Deka 1996; Dooren 1994; Fox 2008; Gottvall 1995; Kriplani 2007; Margulies 1991; Ruma 2007; Ulm 1999; Voto 1997). Ten of these studies concluded that IVIG offers benefit. The first (Chitkara 1990) reported a reduction in disease severity only in one case (involving anti-Kell antibodies), otherwise no benefit of IVIG was identified. Several authors (e.g. Gottvall 1995) have postulated that the reason for this lack of benefit was the lack of early commencement of therapy, suggesting the importance of commencing IVIG treatment before the onset of fetal anaemia.

The largest case series to date included 69 cases retrospectively, and concluded that adjuvant IVIG followed by IUT improved fetal outcomes (Voto 1997). The latest case series was reported in 2009 (Connan 2009), with all six women receiving IVIG as well as intrauterine and/or intraperitoneal transfusions. The use of these treatments in conjunction with serial Doppler ultrasound monitoring led to a delay in the onset of expected invasive therapy in five of the six women, as compared with poor outcomes in previous pregnancies. The majority (five) of women commenced IVIG in the second trimester.

All case series thus far have predominantly involved anti-D alloimmunization. Three studies included women with anti-Kell antibodies (Chitkara 1990; Connan 2009; Fox 2008); one also included a woman with anti-c antibodies as the causal factor for disease (Connan 2009). Based on current limited evidence, there appears to be a potential role for IVIG administration in the management of fetal red blood cell alloimmunization. However, there is a notable lack of comparative trials.

Description of the condition

Since the widespread introduction of routine anti D immunoglobulin prophylactic administration, the incidence of Rhesus D allommunization has decreased dramatically (from 43.3 per 1000 samples of women of reproductive age in the United States in 1967, to 2.6 per 1000 in 1996; Geifman-Holtzman 1997; Queenan 1969). Overall, 1.1% of women in one study from the United States were identified to carry an antibody previously reported to be associated with haemolytic disease of the fetus/newborn (Geifman-Holtzman 1997). When allommunization does occur, it can result in a very difficult disease to treat, often relying on the diagnosis of fetal anaemia and then usually serial invasive procedures to correct the anaemia in-utero. In the absence of treatment, this disease can lead to fetal death.

Current treatment involves IUT, which although potentially life-saving, unfortunately also involves intrinsic procedure-related risks including perinatal mortality.

Description of the intervention

The use of IVIG administered to the mother during the antenatal period.

How the intervention might work

The use of IVIG during the antenatal period may ameliorate the disease and allow later and less frequent red blood cell transfusions to the fetus, thus reducing the invasive procedure-related risk to the pregnancy.

Postulated mechanisms for the efficacy of IVIG in this area include the inhibition of transplacental passage of red blood cell antibodies, and/or a direct Fc blockade of the fetal reticuloendothelial system, thus reducing the degree of fetal phagocytosis of sensitised fetal red blood cells (Clark 1999). Some authors have also suggested that IVIG can downregulate the maternal immune response, for example by increasing suppressor T cell function, thereby inhibiting antibody synthesis (Berlin 1985; Porter 1997). Additionally, IVIG may bind maternal antibodies or enhance their dissociation from antigenic components, decreasing their destructive effects (Ballow 1991).

Why it is important to do this review

A systematic review of the available literature is needed to establish if there is sufficient evidence to establish that IVIG for severe red cell alloimmunization is an efficacious treatment which should be recommended for women with this disease or, if not, to dissuade clinicians from continuing with its use.

Objectives

To systematically review the available evidence on the efficacy and safety of the use of intravenous immunoglobulin (IVIG) antenatally to women with severe fetal red blood cell alloimmunization.

Methods

Criteria for considering studies for this review

Types of studies

Randomized controlled trials and quasi-randomized controlled trials, with parallel study design. Trials with cross-over study design will not be included. If cluster-randomized trials are available, these will also be included. Trials that are published only in abstract form will only be included if the authors are contactable for further details.

Types of participants

Women with red blood cell group antibodies and fetuses at risk of alloimmunization, as defined by past perinatal death secondary to fetal alloimmunization and/or early requirement for intrauterine transfusion (IUT) in previous pregnancies (at less than 20 weeks' gestation).

Types of interventions

  • IVIG(at any dose, frequency or duration) versus no therapy

  • IVIG (at any dose, frequency or duration) versus plasmapheresis (using any regimen)

  • IVIG (at any dose, frequency or duration) versus phenobarbital (at any dose, frequency or duration)

  • IVIG (at any dose, frequency or duration) versus any other therapy

Types of outcome measures

These outcome measures will be applied to all the comparisons, if the trial data allow it.

Primary outcomes
Pregnancy-related
  • Fetal anaemia as diagnosed via cardiotocography (CTG), middle cerebral artery (MCA) Doppler assessment, amniocentesis, fetal blood sampling, or hydrops on ultrasound

  • Gestation at first transfusion

  • Gestation at delivery

Secondary outcomes
Pregnancy-related
  • Number of transfusions

Neonatal
  • Haemoglobin at delivery

  • Admissions to neonatal intensive care unit (NICU) or special care nursery (SCN), and length of stay

  • Treatment after delivery - phototherapy, exchange transfusions, top-ups, IVIG

  • Peak serum bilirubin (corresponding to age in hours)

  • Neonatal survival

  • Complications of treatment

Search methods for identification of studies

Electronic searches

We searched the Cochrane Pregnancy and Childbirth Group’s Trials Register by contacting the Trials Search Co-ordinator (19 December 2012). 

The Cochrane Pregnancy and Childbirth Group’s Trials Register is maintained by the Trials Search Co-ordinator and contains trials identified from: 

  1. monthly searches of the Cochrane Central Register of Controlled Trials (CENTRAL);

  2. weekly searches of MEDLINE;

  3. weekly searches of EMBASE;

  4. handsearches of 30 journals and the proceedings of major conferences;

  5. weekly current awareness alerts for a further 44 journals plus monthly BioMed Central email alerts.

Details of the search strategies for CENTRAL, MEDLINE and EMBASE, the list of handsearched journals and conference proceedings, and the list of journals reviewed via the current awareness service can be found in the ‘Specialized Register’ section within the editorial information about the Cochrane Pregnancy and Childbirth Group

Trials identified through the searching activities described above are each assigned to a review topic (or topics). The Trials Search Co-ordinator searches the register for each review using the topic list rather than keywords. 

Searching other resources

We planned to search reference lists of retrieved articles.

We did not apply any language restrictions.

Data collection and analysis

Methods of data collection and analysis to be used in future updates of this review are provided in Appendix 1.

Results

Description of studies

Results of the search

No trials were found.

Risk of bias in included studies

There are no included studies.

Effects of interventions

There are no included studies.

Discussion

There are no randomized controlled trials examining the administration of immunoglobulin antenatally to prevent complications of red blood cell alloimmunization, although there are some data from case series to suggest its potential benefit. Ten of the 11 case series that have been reported since 1990 produced promising results, with a reduction in disease severity and/or improvement in fetal outcomes. The latest of these series was reported in 2009, with a delay in the onset of expected invasive therapy in five of six patients.

This review demonstrates the continued reliance on case series and first principles in the management of severe fetal red blood cell alloimmunization during pregnancy.

Authors' conclusions

Implications for practice

There is no information currently available from randomized trials to conclude whether the maternal administration of immunoglobulin in the antenatal period confers any benefit compared with other or 'no treatment' for fetal red blood cell alloimmunization. Although this obstetric complication has become less prevalent with the routine use of anti D immunoglobulin, there are still a significant number of cases of fetal anaemia that develop and which can ultimately lead to hydrops or death.

Implications for research

Whilst intrauterine transfusion (IUT) is an effective treatment, its invasiveness and potential risk of procedure-related perinatal mortality justifies further research in this area. In an era when fetal middle cerebral artery (MCA) Doppler assessment has eliminated the need for amniotic fluid evaluation, thus rendering the assessment of alloimmunization far less invasive, further reduction of the need for intrauterine manipulation would be the logical next step. Trials are needed to establish an evidence base toward this prospect. Of relevance would be whether proposed treatments such as intravenous immunoglobulin can be administered safely, and whether such treatment may be effective in successive pregnancies.

Acknowledgements

As part of the pre-publication editorial process, this review has been commented on by three peers (an editor and two referees who are external to the editorial team) and the Group's Statistical Adviser.

The National Institute for Health Research (NIHR) is the largest single funder of the Cochrane Pregnancy and Childbirth Group.  The views and opinions expressed therein are those of the authors and do not necessarily reflect those of the NIHR, NHS or the Department of Health.

Data and analyses

Download statistical data

This review has no analyses.

Appendices

Appendix 1. Methods to be used in future updates of this review

Data collection and analysis

Selection of studies

Two review authors will independently assess for inclusion all the potential studies we identify as a result of the search strategy. We will resolve any disagreement through discussion or, if required, we will consult third review author.

Data extraction and management

We will design a form to extract data. For eligible studies, two review authors will extract the data using the agreed form. We will resolve discrepancies through discussion or, if required, we will consult a third review author. We will enter data into Review Manager software (RevMan 2011) and check for accuracy.

When information regarding any of the above is unclear, we will attempt to contact authors of the original reports to provide further details.

Assessment of risk of bias in included studies

Two review authors will independently assess risk of bias for each study using the criteria outlined in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011). We will resolve any disagreement by discussion or by involving a third assessor.

(1) Random sequence generation (checking for possible selection bias)

We will describe for each included study the method used to generate the allocation sequence in sufficient detail to allow an assessment of whether it should produce comparable groups.

We will assess the method as:

  • low risk of bias (any truly random process, e.g. random number table; computer random number generator);

  • high risk of bias (any non-random process, e.g. odd or even date of birth; hospital or clinic record number);

  • unclear risk of bias.   

(2) Allocation concealment (checking for possible selection bias)

We will describe for each included study the method used to conceal allocation to interventions prior to assignment and will assess whether intervention allocation could have been foreseen in advance of, or during recruitment, or changed after assignment.

We will assess the methods as:

  • low risk of bias (e.g. telephone or central randomization; consecutively numbered sealed opaque envelopes);

  • high risk of bias (open random allocation; unsealed or non-opaque envelopes, alternation; date of birth);

  • unclear risk of bias.   

(3.1) Blinding of participants and personnel (checking for possible performance bias)

We will describe for each included study the methods used, if any, to blind study participants and personnel from knowledge of which intervention a participant received. We will consider that studies are at low risk of bias if they were blinded, or if we judge that the lack of blinding would be unlikely to affect results. We will assess blinding separately for different outcomes or classes of outcomes.

We will assess the methods as:

  • low, high or unclear risk of bias for participants;

  • low, high or unclear risk of bias for personnel;

(3.2) Blinding of outcome assessment (checking for possible detection bias)

We will describe for each included study the methods used, if any, to blind outcome assessors from knowledge of which intervention a participant received. We will assess blinding separately for different outcomes or classes of outcomes.

We will assess methods used to blind outcome assessment as:

  • low, high or unclear risk of bias.

(4) Incomplete outcome data (checking for possible attrition bias due to the amount, nature and handling of incomplete outcome data)

We will describe for each included study, and for each outcome or class of outcomes, the completeness of data including attrition and exclusions from the analysis. We will state whether attrition and exclusions were reported and the numbers included in the analysis at each stage (compared with the total randomized participants), reasons for attrition or exclusion where reported, and whether missing data were balanced across groups or were related to outcomes. Where sufficient information is reported, or can be supplied by the trial authors, we will re-include missing data in the analyses which we undertake.

We will assess methods as:

  • low risk of bias (e.g. no missing outcome data; missing outcome data balanced across groups);

  • high risk of bias (e.g. numbers or reasons for missing data imbalanced across groups; ‘as treated’ analysis done with substantial departure of intervention received from that assigned at randomization);

  • unclear risk of bias.

(5) Selective reporting (checking for reporting bias)

We will describe for each included study how we investigated the possibility of selective outcome reporting bias and what we found.

We will assess the methods as:

  • low risk of bias (where it is clear that all of the study’s pre-specified outcomes and all expected outcomes of interest to the review have been reported);

  • high risk of bias (where not all the study’s pre-specified outcomes have been reported; one or more reported primary outcomes were not pre-specified; outcomes of interest are reported incompletely and so cannot be used; study fails to include results of a key outcome that would have been expected to have been reported);

  • unclear risk of bias.

(6) Other bias (checking for bias due to problems not covered by (1) to (5) above)

We will describe for each included study any important concerns we have about other possible sources of bias. We will assess whether each study was free of other problems that could put it at risk of bias:

  • low risk of other bias;

  • high risk of other bias;

  • unclear whether there is risk of other bias.

(7) Overall risk of bias

We will make explicit judgements about whether studies are at high risk of bias, according to the criteria given in the Cochrane Handbook (Higgins 2011). With reference to (1) to (6) above, we will assess the likely magnitude and direction of the bias and whether we consider it is likely to impact on the findings. We will explore the impact of the level of bias through undertaking sensitivity analyses - see 'Sensitivity analysis'. 

Measures of treatment effect

Dichotomous data

For dichotomous data, we will present results as summary risk ratio with 95% confidence intervals. 

Continuous data

For continuous data, we will use the mean difference if outcomes are measured in the same way between trials. We will use the standardised mean difference to combine trials that measure the same outcome, but use different methods.  

Ordinal data

For ordinal data, we will use the mean difference if outcomes are measured in the same way between trials. We will use the standardised mean difference to combine trials that measure the same outcome, but use different methods. The outcome 'Number of transfusions' will be treated this way.

Unit of analysis issues

Cluster-randomized trials

We will include cluster-randomized trials in the analyses along with individually-randomized trials. We will adjust their standard errors using the methods described in the Cochrane Handbook using an estimate of the intracluster correlation co-efficient (ICC) derived from the trial (if possible), from a similar trial or from a study of a similar population. If we use ICCs from other sources, we will report this and conduct sensitivity analyses to investigate the effect of variation in the ICC. If we identify both cluster-randomized trials and individually-randomized trials, we plan to synthesise the relevant information. We will consider it reasonable to combine the results from both if there is little heterogeneity between the study designs and the interaction between the effect of intervention and the choice of randomization unit is considered to be unlikely.

We will also acknowledge heterogeneity in the randomization unit and perform a subgroup analysis to investigate the effects of the randomization unit.

Cross-over trials

Cross-over trials will not be included in this review.

Multiple pregnancies

If a trial includes women with multiple pregnancies, the data will be identified separately and excluded from analysis.

Multi-armed trials

If there is a trial with multiple intervention groups, groups will be combined to create a single pair-wise comparison.

Dealing with missing data

For included studies, we will note levels of attrition. We will explore the impact of including studies with high levels of missing data in the overall assessment of treatment effect by using sensitivity analysis.

For all outcomes, we will carry out analyses, as far as possible, on an intention-to-treat basis, i.e. we will attempt to include all participants randomized to each group in the analyses, and all participants will be analysed in the group to which they were allocated, regardless of whether or not they received the allocated intervention. The denominator for each outcome in each trial will be the number randomized minus any participants whose outcomes are known to be missing. 

Assessment of heterogeneity

We will assess statistical heterogeneity in each meta-analysis using the T2, I² and Chi² statistics. We will regard heterogeneity as substantial if an I2 is greater than 30% and either a T2 is greater than zero, or there is a low P value (less than 0.10) in the Chi² test for heterogeneity. 

Assessment of reporting biases

If there are 10 or more studies in the meta-analysis, we will investigate reporting biases (such as publication bias) using funnel plots. We will assess funnel plot asymmetry visually, and use formal tests for funnel plot asymmetry. For continuous outcomes, we will use the test proposed by Egger 1997, and for dichotomous outcomes, we will use the test proposed by Harbord 2006. If asymmetry is detected in any of these tests or is suggested by a visual assessment, we will perform exploratory analyses to investigate it.

Data synthesis

We will carry out statistical analysis using the Review Manager software (RevMan 2011). We will use fixed-effect meta-analysis for combining data where it is reasonable to assume that studies are estimating the same underlying treatment effect: i.e. where trials are examining the same intervention, and the trials’ populations and methods are judged sufficiently similar. If there is clinical heterogeneity sufficient to expect that the underlying treatment effects differ between trials, or if substantial statistical heterogeneity is detected, we will use random-effects meta-analysis to produce an overall summary if an average treatment effect across trials is considered clinically meaningful. The random-effects summary will be treated as the average range of possible treatment effects and we will discuss the clinical implications of treatment effects differing between trials. If the average treatment effect is not clinically meaningful, we will not combine trials.

If we use random-effects analyses, the results will be presented as the average treatment effect with 95% confidence intervals, and the estimates of  T2 and I2.

Subgroup analysis and investigation of heterogeneity

If we identify substantial heterogeneity, we will investigate it using subgroup analyses and sensitivity analyses. We will consider whether an overall summary is meaningful, and if it is, use random-effects analysis to produce it.

If sufficient data are available, we plan to carry out the following subgroup analyses.

  1. Women with alloimmunization in previous pregnancies versus those without a relevant past history

  2. Intravenous immunoglobulin used as adjuvant versus where used as sole treatment

  3. Women with Kell alloimmunization versus alloimmunization with other red blood cell antibodies

If quasi-randomized or cluster-randomized studies are included, subgroup analyses will also be conducted.

The following outcomes will be used in subgroup analysis.

  • Fetal anaemia

  • Gestation at first transfusion

  • Number of transfusions

  • Gestation at delivery

We will assess subgroup differences by interaction tests available within RevMan (RevMan 2011). We will report the results of subgroup analyses quoting the χ2 statistic and P value, and the interaction test I² value.

Sensitivity analysis

The predefined criteria for sensitivity analysis includes all aspects of quality assessment as mentioned above, including aspects of selection, performance and attrition bias.

As in subgroup analysis, the following outcomes will be used in sensitivity analysis.

  • Fetal anaemia

  • Gestation at first transfusion

  • Number of transfusions

  • Gestation at delivery

Primary analysis will be limited to the prespecified outcomes and subgroup analyses. In the event of differences in unspecified outcomes or subgroups being found, these will be analysed post hoc, but clearly identified as such to avoid drawing unjustified conclusions.

Contributions of authors

This review was drafted by Kae Sheen Wong with input from Kirsten Connan, Shelley Rowlands, Louise Kornman, and Helen Savoia.

Declarations of interest

None known for Kae Sheen Wong.

Dr Kirsten Connan was the principal author for the paper "IVIG - is it the answer? Maternal administration of immunoglobulin for severe fetal red blood cell alloimmunization during pregnancy: A case series". This article has been accepted for publication with the Australian and New Zealand Journal of Obstetrics and Gynaecology. Three other review authors (Shelley Rowlands, Louise H Kornman and Helen F Savoia) were also co-authors on the same paper.

Dr Helen Savoia has, in the past eight years, and is currently employed on a casual basis by Australian Red Cross Blood Service (ARCBS) for the provision of transfusion medicine advice. ARCBS is the sole provider of fresh blood products in Australia and provides plasma to CSL Bioplasma for the manufacture of intravenous immunoglobulin.

Differences between protocol and review

The methods section has been updated to reflect the most recent versions of Review Manager (RevMan 2011) and the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011).

Ancillary