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Observational Study
. 2013 Aug 6;8(8):e70984.
doi: 10.1371/journal.pone.0070984. Print 2013.

Targeted routine antenatal anti-D prophylaxis in the prevention of RhD immunisation--outcome of a new antenatal screening and prevention program

Eleonor Tiblad  1 , Agneta Taune Wikman, Gunilla Ajne, Agneta Blanck, Yvonne Jansson, Anita Karlsson, Elisabeth Nordlander, Bibi Shassti Holländer, Magnus Westgren
Affiliations
Observational Study

Targeted routine antenatal anti-D prophylaxis in the prevention of RhD immunisation--outcome of a new antenatal screening and prevention program

Eleonor Tiblad et al. PLoS One. .

Abstract

Objective: To estimate the incidence of RhD immunisation after implementation of first trimester non-invasive fetal RHD screening to select only RhD negative women carrying RHD positive fetuses for routine antenatal anti-D prophylaxis (RAADP).

Materials and methods: We present a population-based prospective observational cohort study with historic controls including all maternity care centres and delivery hospitals in the Stockholm region, Sweden. All RhD negative pregnant women were screened for fetal RHD genotype in the first trimester of pregnancy. Anti-D immunoglobulin (250-300 µg) was administered intramuscularly in gestational week 28-30 to participants with RHD positive fetuses. Main outcome measure was the incidence of RhD immunisation developing during or after pregnancy.

Results: During the study period 9380 RhD negative women gave birth in Stockholm. Non-invasive fetal RHD genotyping using cell-free fetal DNA in maternal plasma was performed in 8374 pregnancies of which 5104 (61%) were RHD positive and 3270 (39%) RHD negative. In 4590 pregnancies with an RHD positive test the women received antenatal anti-D prophylaxis. The incidence of RhD immunisation in the study cohort was 0.26 percent (24/9380) (95% CI 0.15-0.36%) compared to 0.46 percent (86/18546) (95% CI 0.37 to 0.56%) in the reference cohort. The risk ratio (RR) for sensitisation was 0.55 (95% CI 0.35 to 0.87) and the risk reduction was statistically significant (p = 0.009). The absolute risk difference was 0.20 percent, corresponding to a number needed to treat (NNT) of 500.

Conclusions: Using first trimester non-invasive antenatal screening for fetal RHD to target routine antenatal anti-D prophylaxis selectively to RhD negative women with RHD positive fetuses significantly reduces the incidence of new RhD immunisation. The risk reduction is comparable to that reported in studies evaluating the outcome of non selective RAADP to all RhD negative women. The cost-effectiveness of this targeted approach remains to be studied.

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Conflict of interest statement

Competing Interests: The study was funded by a research grant from Stockholm County Council. The anti-D immunoglobulin used as routine antenatal anti-D prophylaxis was sponsored by the pharmaceutical company Octapharma Nordic AB. Neither the funder nor the sponsor had any role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. This does not alter the authors' adherence to all the PLOS ONE policies on sharing data and materials.

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Figure 1
Figure 1. Study participants and outcomes.
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Grants and funding

This study was funded by a research grant from Stockholm County Council. The anti-D immunoglobulin used as routine antenatal anti-D prophylaxis was sponsored by the pharmaceutical company Octapharma Nordic AB. Neither the funder nor the sponsor had any role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.