A longitudinal study of platelet behaviour and thromboxane production in whole blood in normal pregnancy and the puerperium

Venous thromboembolism in pregnancy and postpartum: an illustrated review

The topic of this review is venous thromboembolism (VTE) during pregnancy and postpartum. The following topics will be addressed: epidemiology and pathophysiology of VTE in pregnancy and postpartum, diagnostic considerations for VTE in pregnancy, indications for prophylactic and therapeutic anticoagulation in pregnancy and postpartum, choice of anticoagulation in pregnancy and breastfeeding, anticoagulation management during labor and delivery, and anticoagulation considerations for assisted reproductive technology.

Pregnancy as a susceptible state for thrombotic microangiopathies

Pregnancy and the postpartum period represent phases of heightened vulnerability to thrombotic microangiopathies (TMAs), as evidenced by distinct patterns of pregnancy-specific TMAs (e.g., preeclampsia, HELLP syndrome), as well as a higher incidence of nonspecific TMAs, such as thrombotic thrombocytopenic purpura or hemolytic uremic syndrome, during pregnancy. Significant strides have been taken in understanding the underlying mechanisms of these disorders in the past 40 years. This progress has involved the identification of pivotal factors contributing to TMAs, such as the complement system, ADAMTS13, and the soluble VEGF receptor Flt1. Regardless of the specific causal factor (which is not generally unique in relation to the usual multifactorial origin of TMAs), the endothelial cell stands as a central player in the pathophysiology of TMAs. Pregnancy has a major impact on the physiology of the endothelium. Besides to the development of placenta and its vascular consequences, pregnancy modifies the characteristics of the women's microvascular endothelium and tends to render it more prone to thrombosis. This review aims to delineate the distinct features of pregnancy-related TMAs and explore the contributing mechanisms that lead to this increased susceptibility, particularly influenced by the "gravid endothelium." Furthermore, we will discuss the potential contribution of histopathological studies in facilitating the etiological diagnosis of pregnancy-related TMAs.

Platelet aggregation in normal pregnancy

It was recently shown that abnormal platelet aggregation (PA) had played a critical role in some adverse pregnancies. Till now reference range for PA in normal pregnancy has not been determined. Furthermore, few study has been conducted to explore the factors related to PA. Our study was performed to assess the reference range of PA in normal pregnancy (150 participants in the second trimester), and to determine whether it differs from that of the controls (38 nonpregnant participants). In addition, this study explored the factors related to PA. The results showed that PA was significantly higher in normal pregnancy than that in the controls (84.40% vs. 80.7%, respectively, P = 0.013). The reference interval for PA in normal pregnancy was 74.75%-94.77%. Hemoglobin (Hb), platelet counts (PLT) and albumin (Alb) were significant lower in normal pregnancy than those in the control group. Moreover, it was found that PA was positively correlated with PLT (r = 0.263, P < 0.001), and negatively correlated with platelet distribution width (PDW) (r = -0.342, P < 0.001) and mean platelet volume (r = -0.296, P < 0.001). Linear correlations between PA and Alb, PDW were proved by linear regression model (LRM). In conclusion, PA was enhanced in normal pregnancy, and Alb and PDW might be the possible contributing factors to PA.

The variation degree of coagulation function is not responsible for extra risk of hemorrhage in gestational diabetes mellitus

BACKGROUND

Gestational diabetes mellitus (GDM) is characterized as glucose intolerance of any degree that begins or first diagnosed during pregnancy. It possesses a higher risk of haemorrhage, which may be caused by the coagulation dysfunction. However, there has been no study focus on how coagulation state changes in the progress of GDM pregnancy. Our study is aimed to assess the association of coagulation function and haemorrhage in GDM.

METHODS

A total of 662 subjects (273 from a population-based study and 389 from a prospective cohort study) were selected to measure mean platelet volume (MPV), platelet distribution width (PDW), platelet (PLT), thrombocytocrit (PCT), prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT), and fibrinogen (FIB). All pregnant individuals were divided into normal glucose tolerance (NGT) controls and GDM patients diagnosed between the 24th and 28th weeks of gestation.

RESULTS

Compared with NGT controls, GDM females showed shortened PT, shortened APTT, and increased blood FIB levels, while the platelet parameters MPV, PDW, PLT, and PCT remained unchanged in mid-pregnancy. By late pregnancy, the platelet parameters MPV, PDW, and PCT were increased in the GDM group compared with the NGT group, while PT and APTT were unchanged.

CONCLUSIONS

The GDM group was hypercoagulable compared with the NGT group rather than hypocoagulable as predicted, but still within the normal range. Therefore, our findings demonstrate that the variation degree of coagulation function is not responsible for extra risk of hemorrhage in GDM, and prevention of hemorrhage should focus on other causes.

Platelet Adhesion and Thrombus Formation in Whole Blood at Arterial Shear Rate at the End of Pregnancy

PROBLEM

Platelet reactivity has not been evaluated in integrated functional testing during normal pregnancy. Here, we analysed platelet functions under arterial shear rate in comparison with static conditions.

METHOD OF STUDY

Thirty pregnant women with uncomplicated pregnancies and 30 healthy non-pregnant women were enrolled in this study. Platelet adhesion to collagen and fibrinogen and subsequent thrombus formation were measured at arterial shear rate in whole blood using a microfluidic and imaging system. Standard light transmission aggregometry, flow cytometry of activation markers in washed platelets and impedance aggregometry in whole blood were also used to assess platelet responsiveness in static conditions.

RESULTS

Compared to non-pregnant controls, thrombus formation on collagen fibres and firm platelet adhesion on fibrinogen under arterial shear rate were significantly reduced in pregnant women. Platelet aggregometry assays in suspension showed a slight increase in platelet reactivity in pregnant women.

CONCLUSION

While platelet aggregometry and platelet activation markers in static conditions show little changes in platelet reactivity, monitoring of platelet adhesion and thrombus growth on collagen or fibrinogen under flow condition in whole blood indicates a significant decrease in pregnant women compared to controls. This decrease might contribute to counteract a hypercoagulable state and to reduce the risk of arterial thrombosis.

Erythrocyte-platelet interaction in uncomplicated pregnancy

Maternal and fetal requirements during uncomplicated pregnancy are associated with changes in the hematopoietic system. Platelets and erythrocytes [red blood cells (RBCs)], and especially their membranes, are involved in coagulation, and their interactions may provide reasons for the changed hematopoietic system during uncomplicated pregnancy. We review literature regarding RBC and platelet membrane structure and interactions during hypercoagulability and hormonal changes. We then study interactions between RBCs and platelets in uncomplicated pregnancy, as their interactions may be one of the reasons for increased hypercoagulability during uncomplicated pregnancy. Scanning electron microscopy was used to study whole blood smears from 90 pregnant females in different phases of pregnancy. Pregnancy-specific interaction was seen between RBCs and platelets. Typically, one or more platelets interacted through platelet spreading and pseudopodia formation with a single RBC. However, multiple interactions with RBCs were also shown for a single platelet. Specific RBC-platelet interaction seen during uncomplicated pregnancy may be caused by increased estrogen and/or increased fibrinogen concentrations. This interaction may contribute to the hypercoagulable state associated with healthy and uncomplicated pregnancy and may also play a fundamental role in gestational thrombocytopenia.

Risk of a thrombotic event after the 6-week postpartum period

BACKGROUND

The postpartum state is associated with a substantially increased risk of thrombosis. It is uncertain to what extent this heightened risk persists beyond the conventionally defined 6-week postpartum period.

METHODS

Using claims data on all discharges from nonfederal emergency departments and acute care hospitals in California, we identified women who were hospitalized for labor and delivery between January 1, 2005, and June 30, 2010. We used validated diagnosis codes to identify a composite primary outcome of ischemic stroke, acute myocardial infarction, or venous thromboembolism. We then used conditional logistic regression to assess each patient's likelihood of a first thrombotic event during sequential 6-week periods after delivery, as compared with the corresponding 6-week period 1 year later.

RESULTS

Among the 1,687,930 women with a first recorded delivery, 1015 had a thrombotic event (248 cases of stroke, 47 cases of myocardial infarction, and 720 cases of venous thromboembolism) in the period of 1 year plus up to 24 weeks after delivery. The risk of primary thrombotic events was markedly higher within 6 weeks after delivery than in the same period 1 year later, with 411 events versus 38 events, for an absolute risk difference of 22.1 events (95% confidence interval [CI], 19.6 to 24.6) per 100,000 deliveries and an odds ratio of 10.8 (95% CI, 7.8 to 15.1). There was also a modest but significant increase in risk during the period of 7 to 12 weeks after delivery as compared with the same period 1 year later, with 95 versus 44 events, for an absolute risk difference of 3.0 events (95% CI, 1.6 to 4.5) per 100,000 deliveries and an odds ratio of 2.2 (95% CI, 1.5 to 3.1). Risks of thrombotic events were not significantly increased beyond the first 12 weeks after delivery.

CONCLUSIONS

Among patients in our study, an elevated risk of thrombosis persisted until at least 12 weeks after delivery. However, the absolute increase in risk beyond 6 weeks after delivery was low. (Funded by the National Institute of Neurological Disorders and Stroke.).

Ultrastructural analysis of platelets during three phases of pregnancy: a qualitative and quantitative investigation

OBJECTIVES

In the past, platelet morphology during normal pregnancy has not been given much attention.

METHODS

Electron microscopy analysis of platelets from 60 pregnant individuals (30 early pregnancy (weeks 8-14) participants and 30 late pregnancy (weeks 36-40) participants which were followed up 6-8 weeks post-partum) were compared to platelets from 30 non-pregnant individuals as well as each other to establish whether differences in platelet morphology exist during pregnancy.

RESULTS

Ultrastructural changes pertaining to the external and internal arrangements of platelets were visible. Fixated platelets showed pseudopodia formation and membrane blebbing. Increased and enlarged open canalicular system pores, pseudopodia formation, platelet spreading, and membrane blebbing were visible in vital platelets. Platelets from pregnancy were tightly packed and internal structures were different from the non-pregnant group. The internal granules showed modification in their occurrence within the cell. The α- and lysosomal granule counts were significantly increased during pregnancy while dense granule and mitochondrial numbers were significantly decreased.

DISCUSSION

This may point to a pregnancy-specific modification. The changes in platelet ultrastructure discerned in this study attribute to the hypercoagulable state associated with pregnancy. All ultrastructural alterations associated with pregnancy persist for at least 2 months after birth.

Physiologic and pathologic changes of platelets in pregnancy

Platelets are key players in haemostasis and thrombus formation. Defects affecting platelets during pregnancy can lead to heterogeneous complications, such as thrombosis, first trimester miscarriage and postpartum haemorrhage. The incidence of complications is increased in women who have heritable platelet function disorders. Modifications of platelet count or platelet functions during normal pregnancy and preeclampsia will be summarized and the management of pregnant women with heritable platelet function disorders will be discussed.

Mechanisms involved in agonist-induced hyperaggregability of platelets from normal pregnancy

There is substantial evidence of increased platelet reactivity in vivo and in vitro during pregnancy. Platelet activation occurs in pregnancy with a risk of the development of preeclampsia. In this study, platelet behavior was studied during 28-40 weeks of gestation in a group of women who remained normotensive and a group of nonpregnant female controls. Platelet aggregation and ATP release stimulated by agonists (i.e. collagen and adenosine 5'-diphosphate) were markedly enhanced in washed platelets from pregnant subjects. Furthermore, the collagen-evoked increase in intracellular Ca(2+) ([Ca(2+)](i)) mobilization in fura-2-AM-loaded platelets was also enhanced in pregnant subjects. Moreover, the binding activity of fluorescein isothiocyanate-triflavin toward the platelet glycoprotein IIb/IIIa complex did not significantly differ between the nonpregnant and pregnant groups. In addition, the amount of thromboxane A(2) (TxA(2)) formation from pregnant subjects was significantly greater than that from nonpregnant subjects in both resting and collagen-activated platelets. On the other hand, prostaglandin E(2) formation in the presence of imidazole in either resting or arachidonic acid (100 microM)-treated platelets did not significantly differ between these two groups. The levels of cyclic AMP formation in both resting and prostaglandin E(1) (10 microM)-treated platelets from pregnant subjects were significantly lower than those in nonpregnant subjects. Nitric oxide production was measured by a chemiluminescence detection method in this study. The extent of nitrate production in either resting or collagen-stimulated platelets from pregnant subjects did not significantly differ from that of platelets from the nonpregnant group. We conclude that the agonist-induced hyperaggregability of platelets from normal pregnancy may be due, at least partly, to an increase in TxA(2) formation and a lowering of the level of cyclic AMP formation, which leads to increased [Ca(2+)](i) mobilization and finally to enhanced platelet aggregation and ATP release.

Platelets from eclampsia patients have reduced membrane microviscosity and lower activities of the signalling enzymes

It has been shown that platelets from patients suffering from eclampsia are hyporesponsive to stimulation by agonists like thrombin and ADP. Although platelet hyporeactivity contributes to the pathogenesis of the disease process, the cause for this is still not known. Platelet aggregation and secretion are membrane-based phenomena initiated by the processes of cell signalling. Hence, to understand the mechanisms underlying platelet hyporeactivity in eclampsia, membrane microviscosity and activities of the signalling enzymes were measured in human platelets stimulated with thrombin. Membrane fluidity was determined from the steady-state fluorescence anisotropy of diphenylhexatriene incorporated in cell membranes. Activities of phospholipase C and protein kinase C in stimulated platelets were assessed from the extents of phosphatidic acid generation and pleckstrin phosphorylation, respectively. Platelet membrane microviscosity in eclampsia (2.3 +/- 0.2 SEM, n = 5) was significantly lower (P < 0.05) than that in the matched gravid control subjects (3.1 +/- 0.2, n = 4). In eclampsia, generation of phosphatidic acid and phosphorylation of pleckstrin were decreased by 25% (P < 0.05, n = 3) and 35% (P < 0.05, n = 3), respectively, after 60 sec of platelet stimulation. It was concluded that the hyporeactive platelets obtained from eclampsia have more fluid membranes and diminished activities of phospholipase C and protein kinase C. In summary, this study shows that alterations in membrane fluidity and activities of the signalling enzymes (phospholipase C and protein kinase C) may contribute to the diminished platelet responsiveness observed in the eclamptic condition.

The anti-haemostatic strategies of the human hookworm Necator americanus

The human hookworm Necator americanus appears to have evolved a number of complementary strategies to overcome the host's haemostatic processes. These include the inhibition of blood coagulation, platelet aggregation and mediator release, and the secretion of fibrinogenolytic enzymes. These strategies presumably allow the parasite to establish the chronic infections so often documented in human populations.

Hypertensive and normal pregnancy: a longitudinal study of blood pressure, distensibility of dorsal hand veins and the ratio of the stable metabolites of thromboxane A2 and prostacyclin in plasma

OBJECTIVE

By combining serial measurements of the circulating concentrations of thromboxane A2 and prostacyclin with measurements of venous distensibility (taken during the pregnancies of both normal women and those with pregnancy induced hypertension or pre-eclampsia), to test the following hypotheses: 1. that changes in the venous plasma ratio of thromboxane (TXB2) and 6-keto-PGF1 alpha would correlate with changes in the blood pressure of women developing and recovering from pregnancy induced hypertension or pre-eclampsia and 2. that changes in venous distensibility would correlate with changes in arterial blood pressure in pregnancy induced hypertension or pre-eclampsia.

DESIGN

Prospective, longitudinal cohort study.

SETTING

John Hunter Hospital clinic, Newcastle, Australia.

SUBJECTS

One hundred and sixty primiparous women, recruited when presenting for their first routine antenatal visit, were investigated at, or close to, 19, 28 and 37 weeks of gestation; a subgroup was also studied in the postnatal period. The measurements of the patients who developed pregnancy induced hypertension or pre-eclampsia were compared with those of controls selected from the cohort.

MAIN OUTCOME MEASURES

Serial measurements of the circulating concentrations of the stable metabolites of thromboxane A2 and prostacyclin (TXB2 and 6-keto-PGF1 alpha, respectively), venous distensibility and immediate (no rest) and resting (for at least 30 min) blood pressures.

RESULTS

There was no significant difference between the subject and control groups at any time during or after the pregnancy in the concentrations of prostaglandin metabolites, their ratio or venous distensibility. In contrast, there was a significant difference between the groups at 19 weeks for immediate and resting readings of diastolic pressure (6 mmHg (95% CI 1.5 to 10.5) and 4 mmHg (95% CI 0.1 to 7.9), respectively). These differences increased through the pregnancy but mean postnatal readings for the groups were almost identical suggesting that the subjects were not intrinsically hypertensive compared with controls. Blood pressures for the subject group, both immediate and resting, were significantly different from the 19 week readings at 28 weeks (diastolic) and at 37 weeks (systolic and diastolic). The only significant change from first readings among controls was in postnatal systolic pressure which was significantly higher than 19 week values, probably reflecting the vasodilatation, with accompanying hypotension, of early, normal pregnancy. This difference was not observed in those who subsequently developed pregnancy induced hypertension or pre-eclampsia.

CONCLUSIONS

Our study was unable to demonstrate differences in circulating metabolites or venous distensibility between normotensive women and those with pregnancy induced hypertension or pre-eclampsia. If pregnancy induced hypertension or pre-eclampsia in humans represents not so much the presence of abnormal constrictor influences as a process initiated by failure of normal vasodilatation in early pregnancy, studies carried out later may detect mainly adaptive and secondary changes.

Platelet size and glycoprotein Ib and IIIa expression in normal fetal and maternal blood

OBJECTIVE

Our purpose was to study platelet size and surface glycoprotein expression in normal fetal and maternal blood throughout pregnancy.

STUDY DESIGN

A cross-sectional study was performed at the Harris Birthright 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 and n = 117, respectively) and from 30 nonpregnant controls. Flow cytometry was used to determine platelet size and glycoprotein Ib and IIIa expression both before and after stimulation with adenosine diphosphate.

RESULTS

Mean platelet size in both fetal and maternal blood was significantly lower than that of nonpregnant controls and decreased with advancing gestation. The surface density of glycoprotein Ib in maternal and fetal platelets was significantly lower than in nonpregnant controls but did not change with gestation. Adenosine diphosphate stimulation of maternal platelets resulted in increased percentage expression and surface density of all glycoproteins, whereas stimulation of control 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 platelet glycoprotein expression and responsiveness to adenosine diphosphate stimulation is increased. Fetal platelets are phenotypically mature from at least 12 weeks' gestation and respond in an adultlike fashion to stimulation with adenosine diphosphate.

Neonatal platelet reactivity and serum thromboxane B2 production in whole blood: the effect of maternal low dose aspirin

OBJECTIVES

Concern has been expressed about possible neonatal side effects after the use of maternal anti-platelet agents in pregnancy, particularly low dose aspirin treatment. We have studied neonatal platelet behaviour using whole blood techniques, and assessed the neonatal effect of the maternal ingestion of 60 mg aspirin daily.

DESIGN

Cross sectional and randomised, double-blind, placebo-controlled.

SETTING

University hospital.

SUBJECTS

1. Eight normal women, studied before conception, and their infants. 2. Twenty-four infants whose mothers had been randomised to receive either 60 mg aspirin daily, or placebo, in double-blind fashion.

METHODS

The Clay Adams Ultra Flo 100 whole blood single platelet counter was employed to measure platelet aggregation in response to various agonists. The platelet release reaction was also measured in whole blood, and serum thromboxane B2 (TxB2) production was measured by radio-immunoassay. Umbilical cord blood samples were obtained at delivery.

RESULTS

1. Neonatal platelet aggregation induced by adrenaline, ADP and platelet activating factor was reduced in comparison with their mothers (P < 0.01), whereas the neonatal platelet release reaction was reduced when stimulated by collagen and U46619 (a thromboxane mimetic) (P < 0.01). Serum TxB2 production was similar in mothers and babies. 2. Neonatal platelet aggregation, release reaction and serum TxB2 production were not significantly reduced in infants exposed to maternal aspirin in comparison with those neonates exposed to maternal placebo. This is in contrast to the effect on maternal platelets.

CONCLUSIONS

Although only a small number of patients were studied, we interpret this as a relative sparing of neonatal platelet reactivity due to the presystemic action of low dose aspirin.

Changes in platelet intracellular free calcium in normal pregnancy

OBJECTIVE

To determine if platelet intracellular free calcium concentration (p.(Ca2+)i) changes with gestation in normotensive, uncomplicated pregnancy.

DESIGN

A prospective, longitudinal study of primigravid pregnant women compared to a large control group consisting of nulliparous nonpregnant volunteers.

SETTING

The antenatal clinic at University Hospital, Queen's Medical Centre, Nottingham.

SUBJECTS

Two groups of women were studied. Thirty-one nulliparous, nonpregnant women not using oral contraception were investigated in the early follicular phase of their menstrual cycles. Also, 24 primigravid women with normotensive, uncomplicated pregnancies were investigated on eight separate occasions during their pregnancies.

RESULTS

A significant increase in mean p.(Ca2+)i was demonstrated by 28 weeks gestation in the pregnant women as compared to the nonpregnant control group and the same individuals when investigated at 12 weeks postpartum (P < 0.05; ANOVA). This change was maximal at 36 weeks gestation (P < 0.001; ANOVA); concentrations had returned to those not significantly different from nonpregnant women by six weeks postpartum.

CONCLUSIONS

Basal platelet (Ca2+)i increases significantly by the third trimester of normal, primigravid pregnancy as compared to pregnancy values and postnatal values. These data mirror the previously described observations of platelet behaviour noting increased activity at this gestation of pregnancy. It may be that the increased basal p.(Ca2+)i indicates that smaller transient signals have to be generated to induce platelet activity, such as shape change, aggregation and exocytosis.

A randomized placebo-controlled study of the effect of low dose aspirin on platelet reactivity and serum thromboxane B2 production in non-pregnant women, in normal pregnancy, and in gestational hypertension

OBJECTIVE

To investigate the effect of 60 mg aspirin daily on platelet reactivity and prostaglandin production in various groups of patients. Similar regimens, which are thought to act through inhibition of platelet thromboxane production, are currently undergoing clinical assessment for the prevention of pre-eclampsia and intrauterine growth retardation.

DESIGN

A prospective randomized placebo controlled study.

SETTING

University Hospital, Nottingham.

SUBJECTS

12 non-pregnant female volunteers, 18 normal primigravidae before 16 weeks gestation and 16 pregnant women admitted with gestational hypertension (GH) at a mean gestation of 38 weeks.

INTERVENTIONS

In the non-pregnant women blood samples were taken before and after a 10-day course of 60 mg aspirin daily. The primigravidae had blood samples taken at 16 weeks and then they were randomized to receive either 60 mg aspirin daily or a matched placebo. Further blood samples were obtained at 28, 32 and 36 weeks.

MAIN OUTCOME MEASURES

Changes in platelet reactivity and release reaction, and serum thromboxane production, were estimated in whole blood.

RESULTS

60 mg aspirin daily significantly inhibited cyclo-oxygenase dependent platelet aggregation, release reaction and serum thromboxane production in non-pregnant and pregnant women, and in women with GH (P less than 0.01). When adrenaline was used as the aggregating agent, the cyclo-oxygenase pathway was recruited in the increased reactivity seen in the third trimester of normal pregnancy, and was sensitive to inhibition by low dose aspirin.

CONCLUSION

Low dose aspirin would appear to be an appropriate agent for the inhibition of platelet reactivity associated with hypertensive pregnancy.

Increased whole blood platelet aggregation in normal pregnancy can be prevented in vitro by aspirin and dazmegrel (UK38485)

OBJECTIVE

To determine the effect of normal pregnancy and the early puerperium on whole blood platelet aggregation and to assess the role of thromboxane A2 (TXA2) in platelet aggregation in pregnancy.

DESIGN

A prospective descriptive study.

SETTING

TCD Medical School, St James's Hospital, Dublin.

SUBJECTS

Twenty healthy primigravidae who remained normotensive during pregnancy and the puerperium.

INTERVENTIONS

20 ml blood samples were obtained serially at 12, 20, 28, 32 and 36 weeks gestation, during established labour and at 1 h, 24 h, 48 h and 6 weeks after delivery.

MAIN OUTCOME MEASURES

Whole blood platelet aggregation in response to aggregating agents ADP, PAF (platelet aggregating factor) collagen, adrenaline and arachidonic acid (AA) at each stage of pregnancy and peuerperium was measured using a particle counting technique. The in vitro effect of aspirin and dazmegrel (thromboxane synthetase inhibitor UK38485) on platelet aggregation in pregnancy was also investigated.

RESULTS

Platelet aggregation in response to collagen, adrenaline, ADP and AA were increased in the last trimester, during labour and at 1 h after delivery but decreased 24-48 h after delivery. Platelet aggregation in response to AA, collagen and adrenalin was reduced by both aspirin and dazmegrel.

CONCLUSIONS

The earliest and most marked increases in platelet aggregation during normal pregnancy were found in response to AA and collagen. These platelet changes were prevented when whole blood was pre-incubated with either aspirin or dazmegrel. This suggests that enhanced production of TXA2 is responsible for increased platelet reactivity in normal pregnancy.

Platelet reactivity and serum thromboxane B2 production in whole blood in gestational hypertension and pre-eclampsia

OBJECTIVE

To determine the nature and extent of changes in platelet reactivity in gestational hypertension and pre-eclampsia (using whole blood techniques which may be more physiological than those previously employed).

DESIGN

Cross-sectional observational study.

SUBJECTS

8 normal primigravidae, 16 women with gestational hypertension and 12 women with pre-eclampsia, studied at around 36 weeks gestation.

RESULTS

Platelet reactivity (aggregation and release reaction) induced by stimulation with adrenaline was decreased in the pre-eclamptic group. Serum thromboxane B2 production was unchanged in both hypertensive groups compared with the control group.

CONCLUSIONS

In the context of evidence of platelet activation in pre-eclampsia, our findings are interpreted as reflecting platelet exhaustion.