Study of platelet indices in pregnancy-induced hypertension

Abstract

Background

Hypertension encountered during pregnancy could be the first sign of a preexisting pathology that can significantly attribute to unfavorable maternal, fetal, and neonatal outcomes. Resolving hypertensive disorders at an early age may not alter the course and proficiency of the disease, but timely detection and treatment can not only prevent hypertensive crisis but also alter unfavorable fetal outcomes. Ipso facto, an early cataloging plays an essential role in predicting the outcome of pregnancy, both for mother and baby. Platelet indices correlate with functional status of platelets and are an emerging risk marker for detecting an impending adverse outcome in pregnancy-induced hypertension (PIH). The aim of this study was to analyze the consociation between platelet indices and severity of PIH.

Methods

A prospective hospital-based study was undertaken on 100 cases diagnosed with PIH (preeclampsia [PE; 88 cases] and eclampsia [12 cases and 100 controls]).

Results

Most cases occurred in the age group of 22–26 years (43.3%) and in primigravidae (55.8%). Analysis of platelet volume indices (PVI) indicated mean platelet volume (MPV), platelet distribution width (PDW), and platelet–large cell ratio (P-LCR) as significant risk factors for developing hypertensive crisis. This was in concordance with the elevated blood pressures.

Conclusion

The study concludes that platelet indices are raised in patients who have PIH as compared with normal pregnancies.

Introduction

Ten to 15 percent cases of maternal mortality, especially in developing countries, can be attributed to hypertensive disorders of pregnancies.¹ Ipso facto, these disorders account for 3–10% of all complications in pregnancies with capricious incidences across various geographical and topographical areas.²

Hypertensive disorders of pregnancies cause unfavorable outcomes and are associated with increased risk of maternal, fetal, and neonatal adversaries such as recurrent abortions, preterm labor, preterm birth, antepartum hemorrhage, postpartum hemorrhage, intrauterine fetal death (IUFD), intrauterine growth restriction (IUGR), cardiovascular disorders, and renal or hepatic dysfunction. These disorders complicate pregnancy to an extent that maternal mortality is high on the cards.³ Categorization of hypertensive disorders of pregnancy is as follows: gestational hypertension, chronic hypertension, preeclampsia (PE), eclampsia, and PE superimposed on preexisting hypertension⁴ (Table 1).

Table 1.

Classification of hypertensive disorders of pregnancy.

Disorder	Clinical presentation	Time of onset
Chronic hypertension	Preexisting hypertension	Exists before pregnancy
Gestational hypertension	i)Systolic BP > 140 mmHg Diastolic BP > 90 mmhg	>20 weeks of pregnancy
	ii) Confirmed by return to normal BP postpartum
	iii) No proteinuria
Preeclampsia	i) BP > 140/90 mmhg	>20 weeks of pregnancy
	ii) Proteinuria
Eclampsia	Preeclampsia with neurological symptoms/seizures	>20 weeks of pregnancy
Preeclampsia/eclampsia superimposed on chronic hypertension	(i) De novo appearance of hypertension after mid-pregnancy (>30 mmHg systolic and >15 mmHg diastolic from baseline)	>20 weeks of pregnancy
	(ii) Proteinuria at least 300 mg/24 h
	(iii) New-onset proteinuria

BP, blood pressure.

Hypertension in pregnancy is defined as a systolic blood pressure of 140 mmHg or greater or a diastolic blood pressure of 90 mmHg or greater. The patient should be in a relaxed state for about several minutes before the readings are taken using an appropriately sized cuff. The values obtained in first place should be reconfirmed and rechecked by taking another reading at a 20-min time interval or on a separate occasion. The disappearance of Korotkoff sound determines the diastolic reading; mere change in the sound has little significance. However, altercation to define blood pressure criteria to diagnose PE still prevails. The experts in this field have argued over the fact that a rapid elevation of blood pressure (30 mmHg systolic or 15 mmHg diastolic) should be considered to label a patient as preeclamptic. According to recent recommendations, it is believed that women who experience such variations in blood pressure cannot be labeled as preeclamptic. However, these cases do warrant close observation and monitoring, especially if the alerting blood pressure values are associated with proteinuria and hyperuricemia.⁵

Blood platelets play critical roles in hemostasis, providing rapid protection against bleeding and catalyzing slower formation of stable blood clots via the coagulation cascade. They are also involved in protection from infection by phagocytosis of pathogens and by secreting chemokines that attract leukocytes. Platelet function is commonly assessed by platelet count, bleeding time, and platelet aggregation or activation. However, defining and measuring in vivo platelet function remains a challenge.⁶

Platelet indices, i.e., platelet distribution width (PDW), platelet–large cell ratio (P-LCR), and mean platelet volume (MPV), have been well utilized for certain conditions such as aplastic anemia, idiopathic thrombocytopenic purpura, and other hematological and myeloproliferative disorders, to assess the prognosis, but they are underutilized for hypertensive crisis.⁷ Platelet hyperactivity and local platelet activation have been suggested to play a role in acute thrombotic events. Platelet size has been observed to be a parameter to emulate platelet activity, which is indirectly measured by these indices. The size of the platelet is directly proportional to its metabolic and enzymatic activity.⁸

There is an exponential arena to utilize the generated parameters well and upto their resourcefulness. Screening of patients with large platelet size can be performed during routine hematological analysis, and the screened patients can be evaluated further for an impending thrombotic event. Such patients can benefit from timely treatment well before the crisis appears by ensuring close monitoring on the basis of altered indices.⁷ The study was undertaken to analyze the relationship between platelet indices and severity of PIH.

Materials and methods

A prospective hospital-based study after preview from the literature was undertaken on a total of 200 pregnant women reporting in the department of obstetric and gynecology. The sample size was collectively calculated for the three parameters to be evaluated. The subjects were in the age group of 18–35 years and in their second or third trimester of pregnancy.

Of 200, 100 cases were selected as study subjects, which included 88 patients with PE and 12 with eclampsia. The other 100 formed the control group. The controls included normotensive pregnant females in their second or third trimester who were healthy and with a live singleton fetus.

Inclusion criteria for preeclampsia (PE)

• 1)Pregnant females with systolic pressure ranging between 140 and 160 mmHg and diastolic equal or greater than 90 mmHg, reconfirmed and rechecked by taking another reading at 20-min interval and then 6 h apart
• 2)When compared with the prepregnancy values, rapid elevation in the systolic blood pressure by 30 mmHg and in the diastolic blood pressure by 15 mmHg
• 3)Proteinuria >300 mg in 24-h urine sample.

Inclusion criteria for eclampsia

• 1)Systolic pressure ≥160 mmHg and diastolic ≥110 mmHg or greater
• 2)> +++ proteinuria in spot urine sample
• 3)5 gm proteinuria or more in 24-h urine sample
• 4)Abnormal liver function test.

Exclusion criteria

• 1)Twin pregnancy
• 2)IUFD
• 3)IUGR
• 4)Bad obstetric history in the past
• 5)Morbid obesity (body mass index >40 kg/m²)
• 6)Neonatal death
• 7)Systemic disease such as insulin-dependent diabetes mellitus, gestational diabetes, cardiovascular disorders, and renal or hepatic dysfunction.

Only after explaining clearly the need for intervention in a language well understood by the subject and after obtaining consent, samples for hematological analysis were drawn from the patients under all aseptic precautions from the antecubital vein using a 5-ml syringe and immediately mixed with EDTA in vacutainers. The samples were run in the five-part differential automated hematology analyzer (Beckman Coulter LH500) within 2 h of venepuncture, and complete blood count analysis of the sample was carried out.

Results

Two hundred cases were included in the study, which were further divided into two groups of 100 patients each. The first group included patients diagnosed with PE (88) and eclampsia (12). The second group included normotensive pregnant females who were taken as controls.

In our study, the mean age (± standard deviation) of the pregnant women (cases) was 24.03 ± 3.22 years and that of the control group was 25.42 ± 3.18 years. Of the 88 cases in the preeclamptic group, 48 were primigravida (54.545%), and 5 females from the eclamptic group of 12 were primigravida (41.666%). In our study, risk factors were not taken into consideration to avoid interference in the actual values generated during screening of the blood samples. The platelet indices, MPV, PDW, and P-LCR, were evaluated in the study subjects and compared with those of the control group (Table 2).

Table 2.

Platelet indices in hypertensive disorders of pregnancy.

Platelet indices	Control group	Preeclampsia	Eclampsia	Fischer F-value	P value
Mean platelet value (fl)	8.45 ± 1.16	10.46 ± 1.02	11.52 ± 2.65	42.66	<0.0001
Platelet distribution width (fl)	11.01 ± 2.34	15.57 ± 2.87	16.34 ± 3.17	42.02	<0.0001
Platelet–large cell ratio (%)	17.21 ± 4.56	28.01 ± 5.92	31.01 ± 6.25	157.60	<0.0001

The mean value of MPV for the control group in our study was 8.45 ± 1.16 fl, mean value for PDW in the control group was 11.01 ± 2.34 fl, and mean value for P-LCR was 17.21 ± 4.56 fl. MPV was highest in the eclamptic group (11.52 ± 2.65 fl) followed by the preeclamptic group (10.46 ± 1.02 fl) when compared with MPV values recorded in the control group. Based on previous similar studies conducted on platelet indices and PIH, a cutoff value of 9.4 fl was taken to make it a dichotomous variable for calculating the statistical association between the recorded MPV and clinical diagnostic category. The values were found to be highly significant (p < 0.0001) in both categories (PE and eclampsia) at 2 degrees of freedom and 95% confidence level when compared with the control group (Table 2).

The mean value for PDW in our study for the control group was 11.01 ± 2.34. The mean of the PDW value was 15.57 ± 2.87 for PE and 16.34 ± 3.17 for the eclamptic group. To convert it into a dichotomous variable for calculating the statistical association between PDW and clinical category, a cutoff value of 12.9 fl was taken. The association between PDW and the study group was found to be statistically significant (p < 0.0001) (Table 2).

The mean value for P-LCR in our study for the control group was 17.21 ± 4.56. The P-LCR recorded in our study for the eclamptic (31.01 ± 6.25) was higher than that for the preeclamptic group (28.01 ± 5.92). The p value (0.0001) when compared with that of the control group was again found to be statistically significant for evaluating the thrombotic profile in a pregnant female (Table 2).

To summarize, on comparison with the control group MPV, PDW, and P-LCR values were elevated proportionally with the severity of PIH.

Discussion

Blood platelets act as the first defense of the body against hemorrhage. When stimulated usually by a break in the endothelial lining of a blood vessel, they are attracted to the defect, round up, develop pseudopods, become sticky, and adhere to the abnormal area.

Platelets adhere to the injured blood vessel to prevent blood loss through a discrete series of steps involving platelet adhesion to the wounded area and platelet activation, i.e., generation of intracellular chemical signals that are initiated by platelet adhesion. These signals cause rapid morphological changes such as extension of pseudopodia, platelet–platelet aggregation, and granule secretion.⁹

This renders platelet indices, such as MPV and PDW, as valuable prognostic markers for thromboembolic diseases and platelet activation.10, 11

The accepted theory for pathogenesis is endothelial dysfunction and platelet activation. In response to endothelial injury, platelets get activated and release contents of alpha granules such as thromboxane A2 and serotonin, leading to vasoconstriction and activation of coagulation cascade. This secondary activation of coagulation combined with a decrease in fibrinolysis and impaired fibrin clearance interferes with the microcirculation of organs such as the placenta, liver, brain, and kidneys. This leads to development of clinical and biochemical features of the disease.¹²

A preview of literature about the role of platelets in diagnosing an impending hypertensive complication in pregnancy reveals conflicting results.

Santos et al.¹³ found that the platelet indices were significantly higher in preeclamptic women than their normotensive counterpart. On the contrary, Karalis et al.¹⁴ found that there was no change in MPV in normotensive and PIH group during the 3rd trimester. But, Singer et al.¹⁵ showed that there is an increase in MPV in patients with moderate or severe hypertension in pregnancy. Giles et al¹⁶ observed that there was significant macrothrombocytosis (MPV>10.4) in hypertensive pregnant women with/without edema and without proteinuria. A study conducted by Yin et al.¹⁷ also showed that MPV in individuals with PIH was higher than that in controls. However, again in conflict with the aforementioned studies, Ceyhan et al.¹⁸ observed no association of complete blood count, platelet count, and MPV with the presence or severity of PE.

A glance at these studies evaluating the significance of platelets indices show varying trends. Therefore, in the present study, an attempt was made to determine the utility of platelet indices in the diagnosis of PIH. A further attempt was made to assess whether these indices can be used as valuable prognostic markers to predict the severity of pregnancy-induced hypertensive disorders.

As stated previously, circulating platelets are very different in size, metabolism, and functional activity. The largest are more reactive and produce a greater quantity of thrombogenic factors.¹⁹

Mean platelet volume (MPV) is the measurement of average size of platelets. The increase of MPV in conditions of increased platelet turnover is probably mediated by several cytokines (interleukins 6 and 11 and thrombopoietin) that affect megakaryocyte ploidy and result in the production of larger and more reactive platelets.²⁰

The MPV values evaluated in our study were 8.45 ± 1.16 fl for the control, 10.46 ± 1.02 fl for PE, and 11.52 ± 2.65 fl for eclampsia group. We found that there was a progressive rise when the values generated in normotensive pregnant women were compared with those of preeclamptic and eclamptic women in the present study. This significant difference in MPV can be attributed to both, complication of PE and the state of pregnancy itself.

This suggests the role of platelets in pathogenesis of hypertensive disorders of pregnancy. Hence, any increase in MPV from the 1st trimester to the 3rd trimester must be carefully monitored to help in early diagnosis so that proper line of management can be chosen and an impending thrombotic event leading to maternal and neonatal morbidity or mortality can be prevented.

Platelet distribution width (PDW) is the distribution width on 20% frequency level with the peak taken as 100%.²¹ The PDW is useful in differentiating reactive thrombocytosis from the essential type, especially when it is combined mathematically with the MPV and platelet count to obtain a discriminant function.²²

Our observations showed that PDW was significantly elevated among the patients as compared with the control group. Dadhich et al.²³ reported similar findings by demonstrating a month-wise increase in PDW in PE group as compared with the normal pregnant group. The exclusive role of PDW in patients with PE and eclampsia is yet to be delved into. The reason for raised PDW is attributed to increase in the turnover of platelets and increase in the bone marrow activity by unknown stimulus.

Platelet large cell ratio (P-LCR), is the ratio of large platelets, exceeding 12 fL discriminator, and is calculated as the ratio of the particle count between the 12-fL fixed discriminator and upper discriminator (UD) to the particle count between lower discriminator and UD.²¹

In literature, extensive studies on P-LCR values are not available because it is a relatively new and underrated platelet parameter. Our study shows there is a statistically significant increase in P-LCR in preeclamptic and eclamptic women when compared with the control group. This suggests activation of bone marrow in these cases from an unknown stimulus.

The incongruous behavior of the platelet indices in various studies may be attributed to the difference in the equipment, principle, and method of automated cell counters.

Limitations of the study

• •Follow-up of the patients was not possible to examine the prognostic value of our findings.
• •Patients with qualitative disorders and causes of reactive platelets were not assessed and will be carried out in future.
• •Platelet function tests could not be conducted on the sample to substantiate our findings further.

Conclusion

A physiological hypercoagulable state is caused by pregnancy. PE triggers complex events in the endogenous coagulative cascades and consumes platelets and fibrinogen. This subsequently activates thrombopoiesis and fibrinolysis. Our study indicated that MPV (cutoff 9.44 fl for PE and 8.87 fl for eclampsia), PDW (cutoff 12.7 fl for PE and 13.17 fl for eclampsia), and P-LCR (cutoff 22.09% for PE and 24.76% for eclampsia) are useful markers, which were significantly raised in patients. Thus, in conclusion, PVI emerges as an important, simple, and effortless tool for diagnosing PE and also useful in predicting severity of PIH.

Conflicts of interest

The authors have none to declare.