THE PREVALENCE OF ALLOANTIBODIES TO HUMAN PLATELET ANTIGENS IN THROMBOCYTOPAENIC PREGNANT WOMEN ATTENDING THE ANTENATAL CLINIC OF NATIONAL HOSPITAL ABUJA, NIGERIA

Abstract

BACKGROUND: Thrombocytopenia in pregnancy is the second most common haematologic
complications seen, with varying aetiologies. Antibodies to human platelet antigens can result in
thrombocytopaenia in pregnancy. These antibodies could have been acquired from exposure to
fetal antigen in previous pregnancies, or via blood transfusions. The alloantibodies can also
destroy fetal platelets resulting in fetomaternal alloimmune thrombocytopaenia.
AIMS AND OBJECTIVES: The study was aimed at determining the prevalence of
thrombocytopaenia in pregnant women and screening for alloantibodies to human platelet
antigens in pregnant women with thrombocytopaenia.
METHODS: Data was collected using a self administered questionnaire. Three milliliters of
EDTA blood sample was collected from each participant for full blood count. The platelet count
for each participant was determined. The pregnant women with thrombocytopaenia as well as
twenty-six pregnant women with normal platelet counts (control) had their plasma tested for
alloantibodies using Monoclonal Antibody-specific Immobilization of Platelet Antigen kit
(MAIPA).
RESULTS: The prevalence of thrombocytopaenia was found to be 1.1% as 4 out of 370
pregnant women were found to have platelet count <100x109/l. The prevalence of platelet
alloantibodies among the four thrombocytopaenic pregnant women was 100%. Among these four
pregnant women with platelet alloantibodies, three pregnant women (75%) had platelet
glycoprotein specific antibodies, while one pregnant woman (25%) had both platelet
glycoprotein specific antibodies and HLA class 1 antibody.

The prevalence of each class of platelet glycoprotein specific antibodies discovered is as follows:
Anti-Gp11b/111a (1), 33.3%; Anti Gp1a/11a (2), 66.6%; AntiGp1b/1X 0%; HLA/Gp1a11a (1),
33.3%. While the specific antibodies to human platelet antigens identified include: Anti
Gp11b/111a (1a, 3a, 4a); antiHPA-1a (1), 33.3%; Anti Gp1a/11a (5a, 5b); anti HPA-5b (2),
66.6%.
Among the control group, the prevalence of alloantibodies to Hpa was 61.5%, where sixteen
out of twenty-six pregnant women were positive for alloantibodies. Among the sixteen pregnant
women who were positive for alloantibodies to Hpa, 13(81.2%) pregnant women had platelet
glycoprotein specific antibodies, while 3 (18.8%) of these pregnant women had HLA class 1
antibodies.
The prevalence of each class of platelet specific glycoprotein antibodies found includes: Anti
Gp11b/111a, in 3 samples (18.8%), Anti Gp1a/11a, in 9 samples (56.3%), Anti Gp 1b/1X in 1
sample (6.3%), (p<0.05). HLA class 1 antibody in 3 samples (18.8%).
The specific antibodies to the human platelet antigens were identified for the samples of the
pregnant women in the control group, who were positive for platelet specific glycoproteins.
The results showed 3 out of the 16 samples which were positive for Anti Gp11b/111a had, Anti
Hpa 1a in 2 samples (12.5%), Anti Hpa 3a in 1 sample (6.3%). Anti Gp 1a/11a had, Anti Hpa 5a
in 1 sample (6.3%), Anti Hpa 5b in 8 samples (50%).
The most common alloantibody present was HPA-5b, which was found in two of the
thrombocytopaenic pregnant women tested, accounting for 50% and two of the pregnant women
in the control group (28.5%). There was a significant relationship between previous blood
transfusion and development of these antibodies (Fishers exact 3E-06, 7.4E-05, 0.0028 P<0.05),

multigravidity also exert a level significance with development of these alloantibodies (Fishers
exact 0.00432, 0.00373, p<0.05).
CONCLUSION: The prevalence of thrombocytopenia in pregnant women is low in this setting.
The prevalence of alloantibodies to human platelet antigens is high among the tested population.
The alloantibodies to human platelet antigen were found in majority of multigravidas than
primigravidas. Previous blood transfusion may have contributed to the presence of these
alloantibodies to human platelet antigens in some of these pregnant women