PLATELET SIZE AND GLYCOPROTEIN IB AND IIIA EXPRESSION IN NORMAL FETALAND MATERNAL BLOOD

OBJECTIVE: Our purpose was to study platelet size and surface glycopro tein expression in normal fetal and maternal blood throughout pregnanc y. STUDY DESIGN: A cross-sectional study was performed at the Harris B irthright Research Centre for Fetal Medicine, King's College Hospital Medical School, London. Fetal and maternal blood samples were obtained from uncomplicated pregnancies at 8 to 42 weeks' gestation (n = 101 a nd n = 117, respectively) and from 30 nonpregnant controls. Flow cytom etry was used to determine platelet size and glycoprotein Ib and IIIa expression both before and after stimulation with adenosine diphosphat e. RESULTS: Mean platelet size in both fetal and maternal blood was si gnificantly lower than that of nonpregnant controls and decreased with advancing gestation. The surface density of glycoprotein Ib in matern al and fetal platelets was significantly lower than in nonpregnant con trols but did not change with gestation. Adenosine diphosphate stimula tion of maternal platelets resulted in increased percentage expression and surface density of all glycoproteins, whereas stimulation of cont rol platelets resulted in increased surface density of glycoprotein Ib and percentage expression of glycoprotein IIIa. Adenosine diphosphate stimulation of fetal platelets resulted in increased surface density of glycoprotein Ib and IIIa. CONCLUSION: Pregnancy is associated with increased thrombocytopoiesis in both the mother and fetus. Maternal pl atelet glycoprotein expression and responsiveness to adenosine diphosp hate stimulation is increased. Fetal platelets are phenotypically matu re from at least 12 weeks' gestation and respond in an adultlike fashi on to stimulation with adenosine diphosphate.