Risk factors for RhD immunisation in a high coverage prevention programme of antenatal and postnatal RhIg: a nationwide cohort study

Abstract

Objective: To evaluate which risk factors for RhD immunisation remain, despiteadequate routine antenatal and postnatal RhIg prophylaxis (1000 IU RhIg) and ad-ditional administration of RhIg. The second objective was assessment of the currentprevalence of RhD immunisations.Design: Prospective cohort study.Setting: The Netherlands.Population: Two-year nationwide cohort of alloimmunised RhD-negative women.Methods: RhD-negative women in their first RhD immunised pregnancy were in-cluded for risk factor analysis. We compared risk factors for RhD immunisation,occurring either in the previous non-immunised pregnancy or in the index preg-nancy, with national population data derived from the Dutch perinatal registration(Perined).Results: In the 2-year cohort, data from 193 women were eligible for analysis.Significant risk factors in women previously experiencing a pregnancy of an RhD-positive child (n = 113) were: caesarean section (CS) (OR 1.7, 95% CI 1.1–2.6), peri-natal death (OR 3.5, 95% CI 1.1–10.9), gestational age >42 weeks (OR 6.1, 95% CI2.2–16.6), postnatal bleeding (>1000 ml) (OR 2.0, 95% CI 1.1–3.6), manual removal ofthe placenta (MRP) (OR 4.3, 95% CI 2.0–9.3); these factors often occurred in combi-nation. The miscarriage rate was significantly higher than in the Dutch population(35% versus 12.-5%, P < 0.001).Conclusion: Complicated deliveries, including cases of major bleeding and surgicalinterventions (CS, MRP), must be recognised as a risk factor, requiring estimationof fetomaternal haemorrhage volume and adjustment of RhIg dosing. The highermiscarriage rate suggests that existing RhIg protocols need adjustment or bettercompliance.