Thrombosis Research 134 (2014) 1004–1007

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Regular Article

Effects of vaginal delivery, cesarean section and exposure to labor on endothelial function of pregnant women☆,☆☆ Hisaaki Kobayashi a,b,⁎, Gregory Reid c,d, Marie Hadfield c,d a

Department of Obstetrics, Nishisaitama chuo National Hospital, Tokorozawa, Saitama, Japan Department of Gynecology, Nishisaitama Chuo National Hospital, Tokorozawa, Saitama, Japan Department of Obstetrics, University of Manitoba, Health Sciences Centre, Winnipeg, MB, Canada d Department of Gynecology & Reproductive Sciences, University of Manitoba, Health Sciences Centre, Winnipeg, MB, Canada b c

a r t i c l e

i n f o

Article history: Received 31 July 2014 Accepted 28 August 2014 Available online 8 September 2014 Keywords: Cesarean section Endothelial function Flow-mediated vasodilatation Post-term pregnancy Vaginal delivery

a b s t r a c t Introduction: This study was undertaken to assess the influence of labor and cesarean section on endothelial function. Materials and Methods: Flow-mediated vasodilatation (FMD) was measured before and after delivery for an assessment of endothelial function in three groups: (1) the Vaginal delivery group (with spontaneous labor or induction of labor, n = 48), (2) the Elective C/S group (with a cesarean planned, n = 20), and (3) the C/S after FP group (scheduled for vaginal delivery but required to have an emergency cesarean section because of failure in progress, n = 11). Results: There were statistically significant changes between the antepartum and postpartum FMD values in the Vaginal delivery group and the Elective C/S group but not in the C/S after FP group (P b 0.001, P = 0.023 and P = 0.22 respectively). Conclusions: These observations suggest that labor may enhance endothelial function and that cesarean section may impair endothelial function. © 2014 Elsevier Ltd. All rights reserved.

Introduction Endothelial dysfunction is considered as a risk factor or sign of several diseases, such as coronary arteriosclerosis [1] and diabetes mellitus [2]. Similarly, in the obstetrical field, it has been already known that preeclampsia is associated with relative placental underperfusion, which may produce unknown substances leading to endothelial dysfunction [3]. Zanardo et al. [4] have recently demonstrated that higher plasma concentrations of homocysteine, which inhibits endothelial production of nitric oxide (NO) and leads to endothelial dysfunction [5], have been observed in women following cesarean section under general anesthesia as opposed to following vaginal delivery. Abbreviations: C/S, cesarean section; FP, failure in progress; FMD, Flow-mediated vasodilatation; NO, nitric oxide; RBC, red blood cell; VTE, venous thromboembolism; NGF, Norsk Gynekologisk Forening; RCOG, the Royal College of Obstetrics and Gynecology; PPHN, persistent pulmonary hypertension of newborn; BPD, bronchopulmonary dysplasia. ☆ Conducted in Winnipeg, Manitoba, Canada. ☆☆ Conducted at the University of Manitoba, Manitoba Health Science Centre, Departments of Obstetrics, Gynecology & Reproductive Sciences. ⁎ Corresponding author at: Departments of Obstetrics and Gynecology, Nishisaitama chuo National Hospital, 2-1671, Wakasa, Tokorozawa, Saitama, 359-1151, Japan. Tel.:+ 81 4 2948 1111 (Business); fax: + 81 4 2948 1121. E-mail addresses: [email protected], [email protected] (H. Kobayashi).

http://dx.doi.org/10.1016/j.thromres.2014.08.029 0049-3848/© 2014 Elsevier Ltd. All rights reserved.

Buhimschi et al. [6] have also demonstrated that maternal RBC glutathione, an indicator of the redox balance, increased significantly after vaginal delivery at term whereas elective cesarean section did not have the same effect on maternal RBC glutathione. Oxidative stress via oxygen free radical production contributes to the depletion of NO and finally leads to endothelial dysfunction [7–9]. These observations suggest that labor promotes endothelial function while an operated delivery impairs it. Indeed, endothelial function can also be assessed directly and non-invasively using high-resolution ultrasound to measure the increase in diameter of the radial artery in response to reactive hyperemia [10]. This is produced by inflating a blood pressure cuff around the arm to above systolic pressure for five minutes, and then deflating it. The increased flow, over baseline, following deflation of the cuff (flow-mediated vasodilatation) is largely attributed to synthesis of the vasodilator nitric oxide within endothelial cells [11]. Endothelial function in accessible peripheral arteries has been found to correlate to that in the coronary arteries [12]. To observe the effects of delivery, cesarean section, and exposure to labor on endothelial function of pregnant women, the present study measured flow-mediated vasodilatation (FMD) of the radial artery before and after delivery in subjects having elective cesarean section under regional anesthesia at term, and in a comparison group having vaginal delivery.

H. Kobayashi et al. / Thrombosis Research 134 (2014) 1004–1007

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Materials and Methods

Results

Subjects

Study Population

From May 2006 to March 2007, we measured FMD in two cohorts of pregnant women. One cohort was of women having a planned elective cesarean delivery at term. The other cohort was of women past 41 weeks gestation, in whom spontaneous or induced labor was expected within the next two weeks. The Biomedical Research Ethics Board of the University of Manitoba approved this study, and all enrolled subjects signed a written informed consent. The observed subjects were organized into three groups. The Elective C/S group was comprised of subjects who were recruited when they presented for their pre-operative anesthetic assessment and blood work. Only subjects with a gestational age greater than 37 weeks at time of delivery and with cesarean planned within the next two weeks were enrolled. The Vaginal delivery group was comprised of subjects who were recruited when they presented for fetal biophysical testing because of a gestational age greater than 41 weeks, and who subsequently resulted in a scheduled vaginal delivery. Finally, subjects scheduled for vaginal delivery but who were required to have an emergency cesarean section because of failure in progress comprise the C/S after FP group. Subjects with multi-fetal pregnancies, hypertension, diabetes mellitus, smoking, or a history of venous thrombosis were not enrolled.

Of the 104 initially enrolled subjects, 25 did not return for secondary follow up (a second measurement) and were excluded from the analysis. Thus, at the end of the recruitment period, we examined data from79 subjects who were comprised of 48subjects who subsequently resulted in a scheduled vaginal delivery (the Vaginal delivery group), 20 subjects who had an elective cesarean section (the Elective C/S group), and 11subjects who failed due to intra-partum complications and delivered by cesarean section (the C/S after FP group).

Procedures For FMD measurements, an ultrasound system with a 30 MHz mechanical linear probe (SSD-550; Aloka Co., Ltd., Tokyo) was used. The technique for measuring FMD has been previously described [13]. Briefly, an ultrasonographic image of the radial artery was obtained using a probe, which was coupled to the skin using sonographic gel and held in place, under very light pressure, by a mechanical arm. Subjects lay at rest for 5 minutes before the examination. A 140 mm width blood pressure cuff was placed on the upper arm and inflated to 30 mm Hg above systolic pressure for 5 minutes. The radial artery diameter was measured before cuff inflation and over a period of six minutes at one minute intervals after deflation. FMD was calculated as the maximum post-deflation radial artery diameter divided by the pre-inflation diameter ([maximum radial artery diameter]/[baseline radial artery diameter] × 100%). In each of the three groups, FMD was measured twice, before and after delivery. The ante-partum measurement was made within one week before delivery, and the post-partum measurement was made between 6 and 48 hours after delivery.

Characteristics of Subjects Table 1 presents the demographic characteristics for the three study groups. Only between the vaginal delivery group and the Elective C/S group was there a significant difference in maternal age (P = 0.04). The Elective C/S group delivered significantly earlier, compared with the vaginal delivery group and the C/S after FP group (both P b 0.01). There were no differences in any other characteristics than the above among all three groups. Flow-mediated vasodilatation (FMD) In Fig. 1, we present the changes in FMD between the ante- and postpartum in the three study groups. Although FMD of the Elective C/S group decreased after delivery, FMD of the other two groups increased. We found significant changes in FMD between the ante- and post-partum in the Vaginal delivery group and the Elective C/S group, but not in the C/S after FP group (P b 0.001, P = 0.023 and P = 0.22 respectively). In the ante-partum, FMD of the Elective C/S group was higher than that of the other groups (the Elective C/S group 11.30 ± 1.26 % vs. the Vaginal delivery group 5.77 ± 0.68 %, P b 0.001; the Elective C/S group vs. the C/S after FP group 5.09 ± 2.01 %, P = 0.011). On the other hand, in the post-partum, FMD of the Elective C/S group was lowest in the three study groups (the Vaginal delivery group 13.86 ± 0.89 % vs. the Elective C/S group 7.23 ± 1.11 % P b 0.001; the Vaginal delivery group vs. the C/S after FP group 8.01 ± 2.00 %, P = 0.007). As a result of significant difference in the ante-partum FMD, despite all three group being in the same condition before delivery (no complication such as multi-fetal pregnancies, hypertension, diabetes mellitus, smoking, or a history of venous thrombosis), we chose to conduct further analysis as follows.

Table 1 Characteristics of women whose pregnancies were analyzed in the study (n = 79).

Statistical analysis Analyses were performed using the Dr. SPSS II for Windows (11.0.1 J) (SPSS Japan Inc., Shibuya, Tokyo) statistical package. Continuous data was reported as the mean ± SEM. The Levene test was used to assess the homogeneity of variance of the continuous data. Continuous data sets with homogeneous variance were analyzed with the Student t test, one-way analysis of variance (ANOVA), and two-way repeated measure ANOVA as appropriate. The simple main effect analysis was used as a post hoc test for interaction. Continuous data sets without homogeneous variance were analyzed with Kruskal-Wallis ANOVA followed by the Steel-Dwass test. Categorical variables were compared with the χ2 test of independence followed by Bonferroni’s multiple comparison. A probability value of b .05 was considered to indicate a statistically significant difference. Correlation analysis was performed by using coefficient of determination.

Agea pre-preg BMIc pre-del BMIc Birth Weightc (g) Placental Weightc (g) Sexb

Apgar 1minc Apgar 5mina Gestational Age at deliverya (weeks)

Vaginal

Elective C/S

C/S after FP

(n = 48)

(n = 20)

(n = 11)

27.8 ± 0.89 25.6 ± 0.85 30.0 ± 0.87 3683.8 ± 52.9 740.1 ± 20.2 female: 20 (41.66%) male: 28 8.2 ± 0.25 8.9 ± 0.045 41.7 ± 0.051

32.5 ± 1.0 27.4 ± 1.3 31.0 ± 1.2 3463.4 ± 124.0 740.9 ± 42.4 female: 11 (55%) male: 9 8.6 ± 0.19 8.9 ± 0.10 39.0 ± 0.27

30.3 ± 1.0 0.011 28.3 ± 2.2 0.284 33.1 ± 2.1 0.287 3782.9 ± 180.7 0.11 751.4 ± 35.2 0.957 female: 2 0.138 (18.18%) male: 9 7.2 ± 0.67 0.084 8.7 ± 0.20 0.45 41.8 ± 0.20 b0.01

NA, not applicable. a Data presented as mean ± SE and analyzed by Kruskal Wallis ANOVA. b Data presented as n (%) and analyzed by χ2 test of independence. c Data presented as mean ± SE and analyzed by one-way ANOVA.

P value

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H. Kobayashi et al. / Thrombosis Research 134 (2014) 1004–1007

Fig. 1. Changes in FMD between ante- and post-partum in the three study groups. The figure demonstrates the levels of FMD in pregnant women who were classified into the Vaginal delivery group (black squares; n = 48), the Elective C/S group (black triangles; n = 20) and the C/S after FP group (black circles; n = 11). Data is presented as mean ± SEM. Asterisk*, p b 0.001. Pilcrow¶, p = 0.011. Dagger†, p b 0.001. Double dagger‡, p = 0.007.

When they not classified into the three study groups, ante-partum FMD, at term, in all 79 subjects were 11.74 ± 2.74 % (37 weeks, n = 8), 9.81 ± 1.40 % (38 weeks, n = 9), 9.97 ± 1.51 % (39 weeks, n = 7), 9.36 ± 3.46 % (40 weeks, n = 5), 4.92 ± 0.65 % (41 weeks, n = 50). Those measured at 37, 38, 39 and 40 weeks occupy a narrow range of FMD values and also represent a small number of subjects at 8, 9, 7 and 5 cases respectively. The after-41 weeks FMD values seem to be lower than the 37-40 weeks FMD. We, therefore, chose to represent all 79 subjects as two groups and compare them statistically. Accordingly, antepartum FMD measured in 41 weeks 4.92 ± 0.65 % (n = 50) was significantly different from those measured at 37 - 40 weeks 10.30 ± 1.07 % (n = 29) in mean ± SE (P b 0.001). Discussion In vaginal delivery with labor, the Vaginal delivery group, FMD increased after delivery whereas in cesarean section without labor, the Elective C/S group, FMD decreased after delivery. Also, in cesarean section with labor, the C/S after FP group, FMD increased to a lesser extent than vaginal delivery, which took an intermediate value between the other two groups after delivery (Fig. 1). The difference in the gestational age at delivery should explain the reason why ante-partum FMD of the Elective C/S group was significantly higher than that of the other two groups as seen in Fig. 1. The Elective C/S group was measured for FMD before 40 weeks while the other two groups were measured after 41 weeks, when their FMD was found to be significantly lower than the mean FMD measured at 37-40 weeks. Irrespective of the differences in FMD value before delivery, changes in FMD of the Vaginal delivery group and the Elective C/S group were

statistically significant (P b 0.001 and P = 0.023). These changes would be associated with labor and with cesarean section respectively. No significant change was observed in the C/S after FP group, which were exposed to both labor and cesarean section. This may be caused by labor and cesarean effects offsetting each other. In other words, these observations suggest that labor enhances endothelial function and that cesarean section impairs it. The phenomenon that FMD increases after vaginal delivery is consistent with the cited observation that labor at term is associated with increased non-enzymatic anti-oxidant reserve in maternal blood, as measured by RBC glutathione [6]. The negative effect of cesarean section is also consistent with the cited observation that cesarean delivery is associated with increased maternal blood concentrations of homocysteine [4], which is an inhibitor of nitric oxide production. Cesarean section entails a severalfold increase in the risk of venous thromboembolism (VTE) compared with vaginal delivery both around the time of delivery and in the puerperium [14]. This finding is clinically consistent with our results that cesarean section may impair endothelial function, because endothelial dysfunction possibly causes the pathogenic conditions for VTE, which are associated with hyperhomocyteinemia and/or vascular endothelium injury [15,16]. The Norwegian Society of Gynecology and Obstetrics (Norsk Gynekologisk Forening, NGF) recommends prophylaxis with low molecular weight heparin 4-8 days after any cesarean section [17]. Additionally, the Royal College of Obstetrics and Gynecology (RCOG) in the UK classifies women undergoing cesarean section into three degrees, and recommends thromboprophylaxis only for those women classified as medium or high-risk of thrombosis [18]. Both NGF and RCOG approaches entail difficulties of invasive technique and accurate classification respectively. Antioxidant vitamins to improve endothelial function, such as vitamin E [19], may be recommended for patients following cesarean section if endothelial dysfunction by cesarean section indeed causes VTE. Maternal homocysteine levels significantly correlated with cord levels of corresponding delivered neonates [4]. Cord plasma homocysteine levels in cesarean delivered neonates were also significantly higher than vaginally delivered neonates [4]. Hansen et al. [20] showed that elective cesarean section compared with intended vaginal delivery leads to a twofold to fourfold increased risk of overall neonatal respiratory morbidity and even higher relative risks of serious respiratory morbidity in term newborns. They suggested that the mechanism may have been a lack of hormones associated with labor, such as catecholamine and corticosteroids. However, this issue also may be explained if there is a possibility that cesarean section causes neonatal endothelial dysfunction. Further research will be required in this point. In conclusion, we showed statistically significant data which suggest that an operated delivery impaired endothelial function while labor enhanced it. This information should be taken into consideration by women contemplating an elective cesarean section and by the obstetricians counseling them. Conflict of interest None Acknowledgements We acknowledge Martin Reed, MD (FRCPC), for facilitating our use of an ultrasound system with a 30 MHz mechanical linear probe. References [1] Vanhoutte PM. Endothelial dysfunction: The first step toward coronary arteriosclerosis. Circ J 2009;73:595–601. [2] Calles-Escandon J. Cipolla Marilyn. Diabetes and endothelial function: a clinical perspective. Endocr Rev 2001;22:36–52.

H. Kobayashi et al. / Thrombosis Research 134 (2014) 1004–1007 [3] Roberts JM, Lain KY. Recent insights into the pathogenesis of pre-eclampsia. Placenta 2002;23:359–72. [4] Zanardo V, Caroni G, Burlina A. Higher homocysteine concentrations in women undergoing caesarean section under general anesthesia. Thromb Res 2003;112:33–6. [5] Stuhlinger MC, Oka RK, Graf EE, Schmölzer I, Upson BM, Kapoor O, et al. Endothelial dysfunction induced by hyperhomocyst(e)inemia: Role of asymmetric dimethylarginine. Circulation 2003;108:933–8. [6] Buhimsci IA, Buhimsci CS, Pupkin M, Weiner CP. Beneficial impact of term labor: Nonenzymatic antioxidant reserve in human fetus. Am J Obstet Gynecol 2003;189: 181–8. [7] Bechara C, Wang X, Chai H, Peter HL, Yao Qizhi, Chen C. Growth-related oncogene-α induces endothelial dysfunction through oxidative stress and downregulation of eNOS in porcine coronary arteries. Am J Physiol Heart Circ Physiol 2007;293: H3088–95. [8] Pecháňova O, Šimko F. The role of nitric oxide in the maintenance of vasoactive balance. Physiol Res 2007;56:S7–S16. [9] Landmesser U, Spiekermann S, Dikalov S, Tatge H, Wilke R, Kohler C, et al. Vascular oxidative stress and endothelial dysfunction in patients with chronic heart failure: Role of xanthine-oxidase and extracellular superoxide dismutase. Circulation 2002;106:3073–8. [10] Kobayashi H, Yoshida A, Kobayashi M, Nakao S. Non-invasive detection of endothelial dysfunction with 30 MHz transducer. Lancet 1996;347:1336–7. [11] Moens AL, Goovaerts I, Claeys MJ, Vrints CJ. Flow-mediated vasodilatation: a diagnostic instrument, or an experimental tool? Chest 2005;127:2254–63.

1007

[12] Anderson TJ, Uehata A, Gerhard MD, Meredith IT, Knab S, Delagrange D, et al. Close relation of endothelial function in the human coronary and peripheral circulations. J Am Coll Cardiol 1995;26:1235–41. [13] Yoshida A, Nakao S, Kobayashi M, Kobayashi H. Flow-mediated vasodilation and plasma fibronectin levels in preeclampsia. Hypertension 2000;36:400–4. [14] Hollis B. Prolonged pregnancy. Curr Opin Obstet Gynecol 2002;14:203–7. [15] Kroegel C, Reissig A. Principle mechanisms underlying venous thromboembolism: Epidemiology, risk factors, pathophysiology and pathogenesis. Respiration 2003; 70:7–30. [16] Lee R, Frenkel EP. Hyperhomocysteinemia and thrombosis. Hematol Oncol Clin North Am 2003;17:85–102. [17] Dalaker K, Gjønnes H, Abildgaard U. Thromboemboliske Komplikasjoner. Norsk Gynekologisk forening. Veileder ifødselshjelp 1998. Oslo: Den norsk lægeforening; 1998 72–6. [18] Anonymous. Thrombosis and thromboembolism. Why mothers die. Report on confidential enquiries into maternal deaths in United Kingdom 1997-1999. London: Royal College of Obstetricians and Gynecologists; 2001 49–75. [19] Harris A, Devaraj S, Jialal L. Oxidative stress, alpha-tocopherol therapy, and atherosclerosis. Curr Atheroscler Rep 2002;4:373–80. [20] Hansen AK, Wisborg K, Uldbjerg N. Risk of respiratory morbidity in term infants delivered by elective cesarean section: Cohort study. BMJ 2008;336:85.