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


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.
Department of Clinical Science Intervention and Technology, Division of Obstetrics and Gynecology, Karolinska Institutet, Stockholm, Sweden. eleonor.tiblad@karolinska.se
Eleonor
E
Tiblad
Agneta
A
Taune Wikman
Gunilla
G
Ajne
Agneta
A
Blanck
Yvonne
Y
Jansson
Anita
A
Karlsson
Elisabeth
E
Nordlander
Bibi Shassti
BS
Holländer
Magnus
M
Westgren
D015331:Cohort Studies; D003955:Diagnostic Tests, Routine / Q000706:statistics & numerical data; D005260:Female; D060005:Genotyping Techniques; D006801:Humans; D011247:Pregnancy; D011250:Pregnancy Complications, Hematologic / Q000097:blood / Q000453:epidemiology / Q000517:prevention & control; D011296:Prenatal Diagnosis / Q000379:methods* / Q000706:statistics & numerical data; D012203:Rh Isoimmunization / Q000175:diagnosis* / Q000453:epidemiology / Q000517:prevention & control*; D012204:Rh-Hr Blood-Group System / Q000097:blood / Q000235:genetics; D018029:Rho(D) Immune Globulin / Q000097:blood*; D013548:Sweden / Q000453:epidemiology
D012204:Rh-Hr Blood-Group System; D018029:Rho(D) Immune Globulin