PRENATAL DETERMINATION OF HUMAN PLATELET ANTIGEN TYPE USING DNA AMPLIFICATION FOLLOWING AMNIOCENTESIS

Objectives To demonstrate that fetal human platelet antigen (HPA1) type can be determined, without the need for fetal blood sampling, by amplification of fetal DNA from amniotic fluid cells using polymerase chain reaction and allele specific oligonucleotide hybridisation. Design Oligonucleotide DNA primers were designed to amplify a portion of the platelet glycoprotein GpIIIa gene which spans the site of the single base change which differentiates HPA1a from HPA1b. Specific oligonucleotides were designed to hybridise either to the amplified HPA1a allele or to the HPA1b allele. Amniotic cells were used as the DNA template both directly and following formal isolation of DNA. Fetal HPA1 type, determined by this method in fifteen pregnancies not at risk of perinatal alloimmune thrombocytopaenia, was compared to typing of fetal blood obtained following cordocentesis. The methodology was then used to HPA type the fetus in two pregnancies at risk of the disease. Setting Department of Molecular Biology and Centre for Fetal Care, Queen Charlotte's Hospital. Subjects Fifteen women undergoing amniocentesis and fetal blood sampling for other indications and two women at risk of perinatal allo-immune thrombocytopaenia whose partners were heterozygotes. Results In the 15 control cases and the two clinical cases, determination of fetal HPA1 type from amniotic fluid cells agreed with typing of fetal blood. There was no difference in the efficiency of amplification from amniotic fluid cells directly or from isolated DNA. Conclusions Fetal HPA type may be reliably determined by amplification of DNA from amniotic fluid cells, eliminating the need for fetal blood sampling or immunoglobulin administration when the fetus is HPA1a negative.