International Journal of Gynecology and Obstetrics 131 (2015) 59–62

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CLINICAL ARTICLE

Intrapartum mean platelet volume is not a useful predictor of new-onset delayed postpartum pre-eclampsia Gustavo Vilchez a,⁎, Laura Londra b, Luis R. Hoyos a, Robert Sokol c, Ray Bahado-Singh d a

Department of Obstetrics and Gynecology, Wayne State University/Detroit Medical Center, Detroit, MI, USA Division of Reproductive Endocrinology and Infertility, Department of Gynecology and Obstetrics, Johns Hopkins University School of Medicine, Lutherville, MD, USA Department of Obstetrics and Gynecology, Wayne State University School of Medicine, Detroit, MI, USA d Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Oakland University William Beaumont School of Medicine, Rochester, MI, USA b c

a r t i c l e

i n f o

Article history: Received 26 October 2014 Received in revised form 4 April 2015 Accepted 9 June 2015 Keywords: Mean platelet volume Platelet count Postpartum period Pre-eclampsia

a b s t r a c t Objective: To determine whether intrapartum mean platelet volume (MPV) can predict new-onset delayed postpartum pre-eclampsia. Methods: In a retrospective study, data were obtained for women with delayed postpartum pre-eclampsia (≥ 48 hours after delivery) who attended the Detroit Medical Center, Detroit, MI, USA, between January 2002 and July 2010. Patients were divided into two subgroups: new-onset delayed postpartum pre-eclampsia (no history of hypertensive disorder before 48 hours after delivery) and other late-onset/delayed postpartum pre-eclampsia (history of hypertensive disorders). Cases with no hypertensive disorders paired by delivery date were selected as controls. Receiver operating characteristic (ROC) curves were used to determine whether MPV could distinguish between cases and controls. Results: Data for 130 cases of new-onset delayed postpartum pre-eclampsia, 71 cases of other late-onset/delayed postpartum pre-eclampsia, and 405 controls were collected. MPV was significantly different between the pre-eclampsia subgroups (P = 0.007). ROC curves showed that MPV significantly distinguished new-onset delayed postpartum pre-eclampsia cases (area under the curve 0.6, 95% confidence interval 0.5–0.6; P = 0.02), with a sensitivity and specificity of 58.1% and 55.4%, respectively. Conclusion: Although MPV was significantly lower in women who went on to develop new-onset delayed postpartum pre-eclampsia than among controls, it is not a useful predictor. The low MPV suggests a different mechanism for the development of new-onset delayed postpartum pre-eclampsia. © 2015 Published by Elsevier Ireland Ltd. on behalf of International Federation of Gynecology and Obstetrics.

1. Introduction Pre-eclampsia—a condition that complicates between 2% and 8% of pregnancies [1]—remains a leading cause of maternal morbidity and mortality worldwide. It is estimated that 10%–15% of direct maternal deaths are associated with pre-eclampsia and eclampsia, with little variation across high-, middle-, and low-income countries [1,2]. The pathogenesis of pre-eclampsia remains elusive despite extensive research, although there is evidence suggesting a role for platelets in the disease process [3–5], which is supported by findings showing that the incidence of pre-eclampsia is reduced among high-risk patients who take aspirin from early pregnancy [4,6]. One of the most commonly used laboratory tests for the care of women with hypertensive disorders of pregnancy is complete blood count analysis, allowing the evaluation of an important pre-eclamptic variable—the platelet count—in an inexpensive manner. Besides platelet count, complete blood count analysis provides information on several ⁎ Corresponding author at: Department of Obstetrics and Gynecology, Wayne State University/Detroit Medical Center, 3990 John R, 7-Brush N, Mail Box 165, Detroit, MI 48201, USA. Tel.: +1 313 993 4030; fax: +1 313 993 4116. E-mail address: [email protected] (G. Vilchez).

other hematological indices, but only a handful are considered clinically important, such as hemoglobin, hematocrit, white blood cell count, and mean corpuscular volume. Several other indices, including mean platelet volume (MPV), are often ignored because of a lack of familiarity with their use, the belief that they are of minor importance, and/or their practicability in care. MPV is a measurement of the average platelet size found in blood and has recently been investigated as a possible severity and/or predictive marker for pre-eclampsia, albeit with conflicting results [7–17]. MPV has been consistently found to be significantly increased in patients with pre-eclampsia [7–17], probably due to a compensatory response from the bone marrow which, in the presence of a reduction in platelet numbers due to increased platelet consumption by adhesion and aggregation to the vascular endothelium, releases younger platelets that have a larger volume than do their older counterparts [17–19]. Delayed-onset postpartum pre-eclampsia is defined as pre-eclampsia that develops between 2–42 days after delivery. It can be further divided into new-onset delayed postpartum pre-eclampsia (no antecedent diagnosis of hypertensive disorders during the index pregnancy or between 0–2 days after delivery) and recurrent/persistent delayed-onset (other late-onset) postpartum pre-eclampsia (history of hypertensive disorder in the index pregnancy or first 48 hours after delivery, discharged, and

http://dx.doi.org/10.1016/j.ijgo.2015.04.037 0020-7292/© 2015 Published by Elsevier Ireland Ltd. on behalf of International Federation of Gynecology and Obstetrics.

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subsequently readmitted 2–42 days after delivery with the diagnosis of pre-eclampsia and/or eclampsia) [20]. Most clinical pre-eclampsia research has focused on the prepartum/intrapartum periods, neglecting the postpartum period [21,22], despite the fact that 50% of eclampsia cases have been reported to occur after delivery and 26% of seizures occur more than 48 h after delivery [23,24]. Further, the prevalence of de novo postpartum hypertension or pre-eclampsia has been reported to be up to 27.5% [21], with several studies stressing the need for further research [20,22]. Thus, markers that could aid in the prediction of pre-eclampsia are of great interest. Although the role of MPV as a possible predictive and/or severity marker for pre-eclampsia has been evaluated [7–17], the relationship between intrapartum MPV and the development of delayed-onset postpartum pre-eclampsia remains to be investigated. The main objective of the present study is to determine whether intrapartum MPV can predict the development of this condition. 2. Materials and methods The present study was a case-control investigation of patients discharged from the Detroit Medical Center, Detroit, MI, USA, between January 1, 2002, and July 31, 2010. Patients were identified from the Medical Records Registry of the Detroit Medical Center using the International Disease Classification 9th Edition Coding Criteria [25]. The inclusion criteria for cases were singleton delivery, admission during the postpartum period, and a diagnosis of pre-eclampsia according to the above standard criteria. Exclusion criteria were delivery at another institution and incomplete information. For each case included, two controls, paired by date of delivery, were identified. These controls had no history of hypertension-related disorders during pregnancy or the postpartum period (6 weeks after delivery). The institutional review board of Wayne State University/Detroit Medical Center approved this study and, because of its retrospective case series design, no informed consent was needed. Demographic information (maternal age, ethnic origin, gravidity, parity, and gestational age at delivery), past medical history (smoking status and history of hypertensive-related disorders), neonatal weight and sex, and ancillary laboratory data at admission for delivery (hemoglobin, platelet count, and MPV) were collected and recorded in spreadsheets using Microsoft Excel 2007 (Microsoft, Redmond, WA, USA). Cases were further divided into two subgroups: new-onset delayed postpartum pre-eclampsia (defined as patients with diagnosis of postpartum pre-eclampsia 48 hours after delivery with no history of hypertension-related disorders during pregnancy and within 48 hours of delivery) and other late-onset/delayed postpartum pre-eclampsia (defined by diagnosis of postpartum pre-eclampsia with any history of hypertensive-related disorder during pregnancy or within 48 hours after delivery).

Statistical analysis was performed using SPSS version 16.0 (SPSS Inc, Chicago, IL, USA). The χ2 test was used to compare nominal variables and the independent Student t test was used to compare continuous variables. One-way analysis of variance (ANOVA) was used to compare cases with new-onset delayed postpartum pre-eclampsia, cases with other late-onset/delayed postpartum pre-eclampsia, and controls. Post hoc tests were performed for comparisons between the three groups. Receiver operating characteristic (ROC) curves were constructed by plotting the values for MPV. The inflection points for the ROC curves were used as cutoff values for the identification of late-onset and new-onset postpartum pre-eclampsia; sensitivity and specificity for cutoff values were calculated. P b 0.05 or 95% confidence intervals (CIs) not crossing 1 were considered statistically significant. 3. Results Overall, the medical records of 203 cases and 406 controls were reviewed. Two cases and one control were excluded because of inadequate documentation. Therefore, a total of 201 cases and 405 controls were included in the analysis. Subgroup classification of cases indicated that 130 (64.7%) had new-onset delayed postpartum pre-eclampsia and 71 (35.3%) had other late-onset/delayed postpartum pre-eclampsia. Maternal age was significantly higher and gestational age was significantly lower among patients with postpartum pre-eclampsia than among the controls (P b 0.001 for both) (Table 1). The proportions of patients who were African-American, were nulliparous, and reported tobacco use were significantly higher for cases than for controls (P ≤ 0.02 for all) (Table 1). Statistically significant differences were not observed regarding gravidity, parity, newborn weight and sex, or urine drug screening test results. Maternal age, gravidity, gestational age, newborn weight, and the proportion of patients who were African-American, were nulliparous, and reported tobacco use were different among cases with new-onset delayed postpartum pre-eclampsia, cases with other late-onset/ delayed postpartum pre-eclampsia, and controls (Table 2). Maternal age and gravidity of the new-onset group were statistically higher than the other late-onset and control groups (P b 0.001 and P = 0.01, respectively), and gestational age at delivery and neonatal weight of the other late-onset group was significantly lower than the new-onset and control groups (P b 0.001 for both). Hemoglobin varied significantly by group (P b 0.001) (Table 3). Mean MPV in the new-onset subgroup was significantly lower than in the other late-onset subgroup and control group (P = 0.01) (Table 3). Post hoc comparisons showed that hemoglobin in the other late-onset group was significantly lower than in controls (P = 0.0012). Additionally, MPV was significantly different between the pre-eclampsia subgroups (P = 0.007). Following analysis of the distribution of MPV values, ROC curves were constructed to assess the ability of MPV to predict postpartum

Table 1 Maternal demographics and neonatal outcomes among patients with postpartum pre-eclampsia and controls. Patients with postpartum pre-eclampsia

Maternal age, y Gravidity Parity Gestational age at delivery, wk Newborn weight, g African-American Nulliparous Tobacco use during pregnancy Positive urine drug screen during pregnancy Male newborn a b

P value a

Controls

Number of patients for whom data available

Valueb

Number of patients for whom data available

Valueb

201 198 200 198 193 201 200 200 200 186

28.01 ± 6.75 3.67 ± 2.63 2.59 ± 1.84 38.23 ± 2.51 3144.76 ± 794.2 192 (95.5) 50 (25.0) 40 (20.0) 17 (8.5) 92 (49.5)

405 405 405 405 405 405 405 402 405 405

24.09 ± 4.51 3.23 ± 1.82 2.37 ± 1.29 38.92 ± 1.08 3217.61 ± 410.8 337 (83.2) 65 (16.0) 15 (3.7) 0 193 (47.7)

Student t-test or χ2 test. Values are given as mean ± SD or number (percentage).

b0.001 0.04 0.14 b0.001 0.23 b0.001 0.01 b0.001 – 0.72

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Table 2 Maternal demographics and newborn outcomes among patients with new-onset delayed postpartum pre-eclampsia or other late-onset/delayed postpartum pre-eclampsia, and controls.

Maternal age, y Gravidity Parity Gestational age, wk Neonatal weight, g African-American Nulliparous Tobacco use during pregnancy Positive urine drug screen during pregnancy Male newborn a b

P valuea

New-onset delayed postpartum pre-eclampsia

Other late-onset/delayed postpartum pre-eclampsia

Controls

Number of patients Valueb for whom data available

Number of patients Valueb for whom data available

Number of patients Valueb for whom data available

130 128 129 127 124 130 129 129 130 121

71 70 71 71 69 71 71 71 70 65

405 405 405 405 405 405 405 402 405 405

28.55 ± 6.51 3.88 ± 2.65 2.68 ± 1.76 38.74 ± 1.86 3253.61 ± 688.8 127 (97.7) 25 (19.4) 25 (19.4) 11 (8.5) 64 (52.9)

27.03 ± 7.12 3.29 ± 2.58 2.41 ± 1.97 37.34 ± 3.21 2949.13 ± 928.6 65 (91.5) 24 (33.8) 15 (21.1) 6 (8.6) 28 (43.1)

24.09 ± 4.51 3.23 ± 1.82 2.37 ± 1.29 38.92 ± 1.08 3217.61 ± 410.8 337 (83.2) 65 (16.0) 149 (37.1) 0 193 (47.7)

b0.001 0.01 0.11 b0.001 b0.001 b0.001 b0.001 b0.001 0.77 0.41

One-way analysis of variance test or χ2 test. Values are given as mean ± SD or number (percentage).

Table 3 Laboratory data among patients with new-onset delayed postpartum pre-eclampsia or other late-onset/delayed postpartum pre-eclampsia, and controls.

Hemoglobin, g/L Platelet count, ×103 per μL MPV, fL a

P valuea

New-onset delayed postpartum pre-eclampsia

Other late-onset/delayed postpartum pre-eclampsia

Controls

Number of patients for whom data available

Mean ± SD

Number of patients for whom data available

Mean ± SD

Number of patients for whom data available

Mean ± SD

126 126 124

112.8 ± 14.4 236.10 ± 68.8 9.99 ± 1.5

71 71 67

110.2 ± 14.5 233.14 ± 74.8 10.63 ± 1.4

399 399 390

115.6 ± 12.6 224.91 ± 59.9 10.37 ± 1.4

b0.001 0.18 0.01

One-way analysis of variance test (ANOVA).

pre-eclampsia and new-onset delayed postpartum pre-eclampsia (Fig. 1). The inflection point of the generated area under the ROC curve was 0.5 (95% CI 0.5–0.6; P = 0.32), giving a sensitivity and specificity of 58.1% and 43.8%, respectively. For the new-onset subgroup, the inflection point of the generated area under the ROC curve was 0.6 (95% CI 0.5–0.6; P = 0.02), giving a sensitivity and specificity of 58.1% and 55.4%, respectively.

Fig. 1. Receiver operating characteristic curve for the prediction of new-onset postpartum pre-eclampsia.

4. Discussion Although the findings of the present study unexpectedly indicate that intrapartum MPV among women who subsequently develop new-onset delayed postpartum pre-eclampsia is lower than among controls (albeit within the normal range), the low sensitivity and specificity of this marker indicate that it might not be useful for preeclampsia prediction. The fact that MPV was lower rather than higher, as would be expected according to many prepartum/intrapartum preeclampsia studies [7–15], raises the question of whether new-onset delayed postpartum pre-eclampsia is distinct from hypertensive disorders of pregnancy. Studies of MPV in postpartum pre-eclampsia remain scarce. The relevance of MPV as a possible severity and/or predictive marker for prepartum/intrapartum disease has been investigated, with conflicting results [7–17]. Ahmed et al. [8] found that platelet volume increases in women with pre-eclampsia, unlike during a normal pregnancy, and that pregnant women with a high MPV detected on one random blood sample during the second trimester are at risk of pre-eclampsia. The same was reported by Dundar et al. [13], who found that MPV values were significantly higher among pre-eclamptic women than among their normotensive counterparts after the 24th week of pregnancy and suggested periodic longitudinal MPV monitoring as an aid to predict pre-eclampsia. Walker et al. [9] also found that, among patients with mild pregnancy-induced hypertension in whom MPV was followed serially, there was a significant rise in MPV in those who developed severe disease 1 week before clinical diagnosis. Dundar et al. [13] also reported that a significant MPV increase preceded the diagnosis of pre-eclampsia by approximately 4.6 weeks. Further, both Järemo et al. [7] and Piazze et al. [11] reported that patients with pre-eclampsia had significantly greater MPV values than did controls. Järemo et al. [7] also reported that, among pre-eclamptic women, MPV significantly decreased 3–12 months after delivery—a change not seen in

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normotensive women. Myatt et al. [10] found that MPV was significantly higher in the first trimester of pregnancy among women who later developed pre-eclampsia, but the area under the ROC curve for MPV was 0.54 (95% CI 0.49–0.58) with a sensitivity and specificity of 25% and 80%, respectively. Further, MPV was not significantly associated with the development of severe pre-eclampsia [10]. Nevertheless, Calvert et al. [17] reported that a weekly change in MPV could not be used to predict progression among patients with mild non-proteinuric hypertension. Walker et al. [9] also evaluated MPV values and found no significant differences among normal, mild, moderate, and severe cases of hypertension cases, concluding that platelet volumes at 28–30 weeks of pregnancy could not be used as a screening test. Taking into account the previous studies, it was a reasonable assumption that intrapartum MPV would be elevated in postpartum pre-eclampsia. Therefore, the present results—i.e. the lack of a significant difference between women who had other late-onset/delayed postpartum pre-eclampsia and controls—were surprising because, by definition, the former group has a history of pre-eclampsia in the index pregnancy and several studies have found a significant association between a high MPV and prepartum pre-eclampsia. These findings are in line with those of Ceyhan et al. [16], who did not find a significant difference in MPV between controls and patients with pre-eclampsia. Even more unexpected was the finding of a lower intrapartum MPV for the new-onset subgroup than in the other late-onset group and control group. It must be noted, however, that MPV in the new-onset subgroup was still within the reference range for MPV (7.2–10.8 fL) [26]. Thus, the fact that the ROC curves revealed a non-significant result for delayed-onset postpartum pre-eclampsia prediction as a whole and a low sensitivity and specificity (58.1% and 55.4%, respectively) for newonset pre-eclampsia, was not surprising. The above results confirm that, despite the fact that a low MPV is associated with new-onset postpartum pre-eclampsia, MPV is not a good predictive test for the condition. The present study is limited by its retrospective design. Further, it is a well known fact that ethylenediamine tetraacetic acid—the anticoagulant used for blood specimen collection—can influence platelet size in a time-dependent manner. Nevertheless, blood sample collection and processing is standardized at the Detroit Medical Center and all samples are usually processed quickly; therefore, the present findings reflect these standard clinical conditions. Finally, the fact that ethnic disparities and body mass index can both influence MPV values should also be considered [10]. A particular strength of the present study is the high number of delayed postpartum pre-eclampsia cases included, as well as the differentiation made between new-onset and other late-onset cases, both of which had an adequate sample size. The present results further the understanding of delayed postpartum pre-eclampsia and its sub-entities. The well known predictor of postpartum pre-eclampsia in other late-onset cases—i.e. hypertension in the prepartum and intrapartum periods—allows the careful monitoring of these patients. It is the patients with new-onset delayed postpartum pre-eclampsia who pose a clinical challenge, because no appropriate predictive markers are yet available. The low MPV values indicated in the present study, similar to high MPV for prepartum pre-eclampsia, could reflect the pathogenesis of this condition and suggest that new-onset delayed postpartum pre-eclampsia might be a distinct entity among the hypertensive disorders of pregnancy. Such an interpretation is supported by the different demographic profiles found to characterize the patients who developed new-onset delayed postpartum pre-eclampsia. This reasonable speculation should be further investigated, not through simple clinical studies, but rather through the evaluation of the mechanisms involved. Thus, further studies of new-onset delayed postpartum pre-eclampsia are warranted.

Conflict of interest The authors have no conflicts of interest.

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Intrapartum mean platelet volume is not a useful predictor of new-onset delayed postpartum pre-eclampsia.

To determine whether intrapartum mean platelet volume (MPV) can predict new-onset delayed postpartum pre-eclampsia...
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