Study Supports New Test To Target Pregnancy Blood Disorder
April 4th, 2008 | by admin |According to a study published on bmj.com,researchers have developed a new test that can identify whether amother and her baby have different blood types. Kristin Finning(International Blood Group Reference Laboratory, NHS) and colleaguesmaintain that the test is accurate, feasible, and couldsignificantly reduce unnecessary treatment.
If a mother’s blood type is Rhesus (Rh) negative and she is carrying ababy whose blood is Rh positive, complications can occur. Blood that isRh positive contains an RhD antigen that passes into the mother’s bloodduring birth. This substance causes the mother to make antibodiesagainst the RhD positive blood.
During a woman’s first pregnancy, there are usually no problems due tothe antibodies. However, if the woman has another RhD positive baby,the antibodies can cross the placenta and invade the baby’s red bloodcells. This results in hemolytic disease - a blood disorder that isserious and can cause death.
The preventive measure for this disorder is to test the blood type ofpregnant women at their first antenatal visit. If the woman is RhDnegative, she is given one or two antiserum injections of anti-RhDimmunoglobulin during the pregnancy. Inefficiencies arise in thissystem, however, because about 38% of RhD negative women are carrying ababy who is also RhD; these women receive an unnecessary treatment ofantiserum injections.
To avoid the occurrence of unnecessary treatments, researchersat the NHS Blood and Transplant Centre in Bristol investigated a newway to predict a baby’s blood group by “typing” its DNA in the plasmaof RhD negative pregnant women.
The researchers took blood samples from 1,997 women at or before the 28week doctor visit and found that the correct RhD phenotype of the babywas predicted by genotyping tests in 96% of cases. Confirmation of thiswas made by testing blood samples retrieved from the umbilical cord atdelivery. Fourteen blood samples (0.8%) resulted in false positiveoutcomes and three blood samples (0.2%) were false negatives.Unobtainable or inconclusive results occurred in 3.4% of cases.
The researchers point out that if the results of the test had been usedas a guide for whether or not a woman would receive the antiserumtreatment, only 2% of women would have received anti-RhD withoutnecessity - compared to 36% who unnecessarily receive the antigenwithout genotyping.
“Our results show that fetuses of RhD negative women could be RHDgenotyped with an acceptable level of accuracy,” write the authors.They also point out the low rate of false positiveresults. “The introduction of fetal genotyping followed by thewithholding of antenatal anti-RhD prophylaxis from mothers with an RhDnegative fetus would result in about 36% of women being saved fromunnecessary exposure to human blood products, inconvenience, anddiscomfort.”
Effect of high throughput RHD typing of fetal DNA in maternalplasma on use of anti-RhD immunoglobulin in RhD negative pregnantwomen: prospective feasibility study
Kirstin Finning, Pete Martin, Joanna Summers, EdwinMassey, Geoff Poole, Geoff Daniels
BMJ. (2008).
doi:10.1136/bmj.39518.463206.25
ClickHere to See Article Online
Written by: Peter M Crosta
Copyright: Medical News Today
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