Detectability of Anti-D and Compliance in Two Regimens

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Background, aims & objectives: In some pregnancies, the blood types of mother and baby are not the same – this may cause problems for the baby. The mother’s immune system may ‘see’ the baby’s blood type as a threat, a process called sensitisation. This is called Rhesus disease and can cause anaemia, jaundice, and possibly serious consequences. Ways of preventing Rhesus disease are both safe and well-established, and used as part of regular antenatal care at KEMH. This involves an injection of anti-D antibody to maintain a protective level of this antibody in the blood. This dampens the body’s immune response to the baby’s blood, and greatly reduces the risk of Rhesus disease. With current prevention methods, the risk of Rhesus disease is less than 1%. There are two main approved dosing regimes, 1) the single-dose regime and 2) the double-dose regime. Both have advantages and disadvantages. Currently, Australia uses a double-dose regime, but is considering moving to a single-dose regime. Although widely used in the UK, Europe and USA, the single dose has not been studied locally in Australia. At present, women at KEMH receive two doses of anti-D during their pregnancy. This study will investigate both regimes to identify any difference in protection that lasts up to the time of delivery. A smaller study will review all women with evidence of sensitisation in the last 3 years to identify the possible causes. The results of the studies will help doctors optimise the preventive treatment, and help reduce the impact of Rhesus disease. Study population: Anti-D Dosage Study: We will recruit 300 Rhesus-negative pregnant women who have a negative antibody screen, and have no history of adverse reactions to anti-D injections. Anti-D Sensitization Review: We will recruit women with evidence of sensitisation to the Rhesus-D antigen in the last 3 years. Based on population estimates, there will be up to 30 eligible women for this study in WA. Study design & methods: Anti-D Dosage Study: Three hundred women will be recruited from antenatal clinics in KEMH at <28 weeks of pregnancy. Women will be allocated to one of two groups. The control group will receive standard antenatal care, which includes two injections of anti-D antibody, six weeks apart (at 28 and 34 weeks of gestation). The single-dose group will receive one, larger dose injection of anti-D at 28 weeks. At delivery, all participants will have a blood test which checks for anti-D antibody. All participants will otherwise receive standard care for the prevention of sensitisation, including a) receiving additional anti-D injections after any potential sensitizing events during pregnancy and b) receiving an injection of anti-D antibody after delivery if their baby is Rhesus-positive. Relevant medical information will be extracted from medical records. Anti-D Sensitization Review: All women with evidence of sensitisation to the Rhesus-D antigen in the last 3 years will be interviewed and their medical records reviewed to identify, if possible, the timing and potential contributing factors for sensitisation. Outcomes: This study will provide unique data for the National Blood Authority and Australian clinicians. It will provide information about the proportion of women that still have circulating anti-D at the time of delivery using the Australian two-dose (625IU) regime. This will enable a direct comparison to that achieved by the one-dose (1500IU) regime that is currently being proposed for Australian pregnant women. The sensitization review will also provide information to further advance Rhesus disease prevention in Australia by identifying potential targets for education campaigns. Potential ethical issues: There is minimal risk to participants as the intervention (a single dose of anti-D antibody) is an approved regime used in routine clinical practice in Europe and the USA.