Can we safely stop testing for Rh status and immunizing Rh-negative women having early abortions? A comparison of Rh alloimmunization in Canada and the Netherlands

Objective

The objective of this study was to compare Rh alloimmunization rates in two countries (Canada and the Netherlands) with completely different policies regarding abortion-related use of anti-D immunoglobulin to ultimately determine any benefit in use. In the Netherlands, the policy is to offer anti-D immunoglobulin to Rh-negative women having spontaneous abortions over 10 weeks 0 days gestation and induced abortions over 7 weeks 0 days. In Canada, it is recommended to offer all Rh-negative women having induced or spontaneous abortions anti-D immunoglobulin.

Methods

We used public databases to obtain the population data, the number of births, the abortion rates (the percentage of women having induced abortions in one year) and the Rh-negativity rates (percentage of Rh negative women) in Canada and the Netherlands. Both countries do routine prenatal blood screening and we obtained the rates of clinically significant antibodies from public databases.

Results

In nearly 2 million blood samples from pregnant women in both Canada and the Netherlands, the prevalence of clinically significant antibodies was statistically lower in the Netherlands: 4.21 (95% CI: 4.12 to 4.30) and 4.03 (95% CI: 3.93 to 4.12) per 1000, respectively. Canada and the Netherlands had small differences in rates of abortion (1.9 per 100 vs 1.2 per 100) and of Rh negativity (13.0% vs 14.5%).

Conclusion

Despite different anti-D Ig treatment policies, we found a similar prevalence of clinically significant perinatal antibodies among women in Canada and the Netherlands.

Implications

Our findings suggest that The Dutch policy of not treating Rh-negative women having spontaneous abortions under 10 weeks’ or induced abortions under 7 weeks’ gestation can be safely adopted by other countries.