STRUCTURAL AND FUNCTIONAL ARTERIAL CHANGES IN HEALTHY WOMEN FOLLOWING PREGNANCY: MATERNAL VASCULAR ADAPTATIONS TO PREGNANCY II STUDY
by
Mansi MahirDesai
B.S. in Molecular Biochemistry and Biophysics, Illinois Institute of Technology, 2012
Submitted to the Graduate Faculty of
Graduate School of Public Health in partial fulfillment
of the requirements for the degree of
Master of Public Health
University of Pittsburgh
2015
UNIVERSITY OF PITTSBURGH
GRADUATE SCHOOL OF PUBLIC HEALTH
This essay is submitted
by
Mansi Mahir Desai
on
April 21, 2015
and approved by
Essay Advisor:
EmmaBarinas-Mitchell, PhD______
Assistant Professor
Department of Epidemiology
Graduate School of Public Health
University of Pittsburgh
Essay Reader:
Marnie Bertolet, PhD ______
Assistant Professor
Departments of Epidemiology, Biostatistics, and Clinical and Translational Science Institute
Graduate School of Public Health
University of Pittsburgh
Essay Reader:
JanetCatov, PhD______
Assistant Professor
Departments of Obstetrics, Gynecology and Reproductive Sciences, Epidemiology, and Clinical and Translational Research
School of Medicine
University of Pittsburgh
Copyright © by Mansi M. Desai
2015
Emma Barinas-Mitchell, PhD
STRUCTURAL AND FUNCTIONAL ARTERIAL CHANGES IN HEALTHY WOMEN FOLLOWING PREGNANCY: MATERNAL VASCULAR ADAPTATIONS TO PREGNANCY II STUDY
Mansi M. Desai, MPH
University of Pittsburgh, 2015
ABSTRACT
Background: Parity is associated with increased maternal risk of cardiovascular disease (CVD)in a J-shaped fashion. Vascular adaptation to changes during pregnancy may be an indicator of future CVD risk. The literature indicates that pregnancy results in an increase in common carotid artery inter-adventitial diameter (CCA IAD) and intima-media thickness (CCA IMT), markers of vascular aging and future CVD risk. These changes were found to recede early postpartum, although not consistently and not back to pre-pregnancy levels. This study aims to determine whether vascular changes during pregnancy persist beyond the initial postpartum period.
Methods: This study is a follow-up to a prospective study that assessed vascular health in a cohort of 43 healthy women during each trimester of their first pregnancy and 6-8 weeks postpartum. Data on physical measures, biomarker assays, pregnancy outcomes, and health history were collected 1-5 years following the index birth. B-mode ultrasound was used to measure CCA IAD and CCA IMT. Paired t-tests and multivariable linear regression were used to assess changes in vascular measures.
Results:Sixteen participants with mean age 32.4 years completed the second postpartum visit. The average time from index delivery was 2.7 years. Unadjusted mean CCA IAD slightly decreased and CCA IMT increased at the second postpartum visit compared to the first postpartum and first trimester visits; these changes were notstatistically significant. Long-term postpartum, larger CCA IAD was associated with higher blood pressure whereas thicker CCA IMT was associated with less time since index birth, greater weight change, less time breastfeeding, and lower insulin resistance (p<0.05).
Conclusions:Markers of vascular aging did not improve further out postpartum compared to the early postpartum period. Persistence of vascular effects of pregnancy may suggest a possible mechanism linking increased CVD risk with parity.
Public Health Significance: CVD is the leading cause of death in women. Increased understanding of vascular adaptation during pregnancy may help explain differential future CVD risk with parity and inform early detection of women at increased CVD risk long-term. Prolonged breastfeeding and weight management during pregnancy may be potential lifestyle modifications for women to decrease their future CVD risk.
TABLE OF CONTENTS
prefaceIX
1.0 Introduction...... 1
2.0 MAterials and METHods...... 3
2.1 STUDy Design and population...... 3
2.2 ultrasound assessment of the common carotid artery...... 4
2.3 pregnancy history and CVD risk factors...... 5
2.4 power calculation...... 7
2.5 statistical analysis...... 7
3.0 Results...... 9
3.1 subject characteristics...... 9
3.2 Key vascular measures...... 9
3.3 additional analyses...... 11
4.0 DiSCUSSION...... 18
Appendix: supplementary tables and figures...... 24
bibliography...... 28
List of tables
Table 1. Characteristics of the study population at the second postpartum visit...... 12
Table 2. Unadjusted values for vascular measures and key time-varying covariates by visit...13
Table 3. Vascular measures at second postpartum visit by categories of pregnancy-related covariates 14
Table 4. Adventitial diameter models adjusted for individual predictors at second postpartum visit 15
Table 5. Intima-media thickness models adjusted for individual predictors at second postpartum visit 16
Supplementary Table 1. Baseline demographic characteristics of MVP participants who attended compared to those who did not attend second postpartum visit 24
Supplementary Table 2. Correlations between major outcome variables and other covariates at second postpartum visit 25
List of figures
Figure 1. Flowchart of the study population...... 3
Figure 2. Ultrasound Image of CCA...... 4
Figure 3. Changes in CCA inter-adventitial diameter by visit...... 17
Figure 4. Changes in CCA intima-media thickness by visit...... 17
Supplementary Figure 1. Changes in CCA inter-adventitial diameter for MVP II participants throughout and after pregnancy 26
Supplementary Figure 2. Changes in CCA inter-adventitial diameter for all MVP participants throughout and after pregnancy 26
Supplementary Figure 3. Changes in CCA intima-media thickness for MVP II participants throughout and after pregnancy 27
Supplementary Figure 4. Changes in CCA intima-media thickness for all MVP participants throughout and after pregnancy 27
preface
Sixteen months ago, while discussing with my advisor the several options I could pursue for my master’s internship, the Maternal Vascular Adaptations to Pregnancy II study was born. What seemed like an over-ambitious goal and a long journey could not be accomplished without the help of many people. I am very thankful to my advisor and mentor Emma Barinas-Mitchell who stood by me every step of the way. You have set an example of excellence as a researcher, mentor, and role model. I greatly appreciate all the help from Nancy Niemczyk; without your previous work, this study would not have existed. I am thankful to my mentor Marnie Bertolet for her statistical expertise and support at all times. I would like to thank my essay readers and co-investigators; your constant feedback and encouragement has been absolutely invaluable.
I would like to thank all the staff of the Ultrasound Research Laboratory, Health Studies Research Clinic, and Heinz Nutrition Laboratory for their help, support, and for being so flexible with the needs of this study. I am very grateful to all the study participants, who despite the unpredictable weather and young babies, made it to the study visits.
I would especially like to thank my amazing family for the love, support, and constant encouragement. In particular, I would like to thank my husband, parents, in-laws and sister. You are the sunshine of my life, and I could not have done this without you.
Finally, I would like to dedicate this work to my husband, Mahir, for his remarkable patience, unwavering support, and motivation throughout my graduate program. Thank you for always being there for me.
1
1.0INTRODUCTION
Maternal cardiovascular disease risk rises with increased parity in a J-shaped fashionwith 2 births representing the nadir of risk16,24,25, howeverthe mechanism for this increased risk is unknown. Some of the increased risk may be attributed to behavioral and socioeconomic risk factors related to increased parity.16 In addition, pregnancy may unmask an underlying cardiovascular disease (CVD) susceptibility in some women due to increased stress on the cardiovascular system, with each pregnancy potentially adding to increased cumulative risk.16 The cardiovascular demands of a normal pregnancy are substantial and vascular remodeling is required to handle the increased circulating fluid volume.
During a healthy pregnancy, uterine vasculature remodels in response to a stimuli of hemodynamic, hormonal, and metabolic changes.27Hemodynamic changes starting early in pregnancy include an increase in heart rate, cardiac output and stroke volume; sodium and water retention, which leads to increased blood volume; and decreased blood pressure and systemic vascular resistance.17,18 Hormonal changes during pregnancy include an increase in estrogen, progesterone, testosterone and maternal cortisol concentrations.19,20 Metabolic changes during pregnancy include increased insulin21, triglyceride22, lipid22, and C-reactive protein23 concentrations. Although not well-understood, results from small studies suggest that during pregnancy, systemic arteries adapt to these changes in a similar fashion to the uterine vasculature12,14,17.How the systemic vasculature adapts to these changes during pregnancy may be an indicator of future CVDrisk. Furthermore, many pregnancy complications have a vascular component.38-41Better understanding of the effects of pregnancy on the systemic arteries may lead to early detection of women for pregnancy complications and CVD risk, and help explain the differences in cardiovascular risk found in women of different parity.12
A small number of studies13-15,26 have examined changes in systemic arteries during the course of normal pregnancy, and found that pregnancy results in increased common carotid artery (CCA) intima-media thickness (IMT) and inter-adventitial diameter (IAD), markers of vascular aging30,33 and future CVD risk26,36,37. These changes were found to recede postpartum, although not consistently and not back to pre-pregnancy levels.13-15,26 Many of these studies have been limited by lack of serial vasculature26 and biomarker13-15,26measures throughout normal pregnancy and later postpartum, and use of less well-established techniques to assess changes in the vasculature14.The Maternal Vascular Adaptations to Healthy Pregnancy (MVP) study prospectively assessed vascular health in a cohort of 43 healthy women during each trimester of their first pregnancy and 6-8 weeks postpartum.12Consistent with existing literature, the MVP study found that in uncomplicated first pregnancies, some vascular changes resolved (increased CCA IAD) and others persisted (increased CCA IMT) 6-8 weeks postpartum.12 This persistence maybe because 6-8 weeks postpartum does not represent adequate time to return to baseline. It remains to be explored if this persistence of vascular effects of pregnancy indicates long-term cardiovascular disease risk.12If the increased CCA IMT identified in the MVP study persists long-term, it could be a mechanism by which parity contributes to greater CVD risk.
Thus, the aim of this study was to bring back MVP participants for a second postpartum visitto determine whether the vascular change that occurs during pregnancy, increased CCA IMT, persists beyond the initial postpartum period. We hypothesized that: 1) CCA IAD would decrease long-term postpartum as compared to 6-8 weeks postpartum and 2) CCA IMT would decrease long-term postpartum as compared to 6-8 weeks postpartum. Our secondary hypotheses were that: 1) CCA IAD would decrease long-term postpartum as compared to first trimester (baseline) and 2) CCA IMT would decrease long-term postpartum as compared to first trimester (baseline).
2.0 MATERIALS AND METHODS
2.1 Study Design and Population
The Maternal Vascular Adaptations to Pregnancy II (MVP II) study is a follow-up study to the MVP study. MVP study visits were scheduled at 12-14 weeks, 24-26 weeks and 36-38 weeks of pregnancy, and then at 6-8 week postpartum.The MVP II study visit took place between 1 and 5 years after the index delivery. This is the second postpartum visit for the MVP study participants.
44 women enrolled in MVP Study
1 dropout
43 eligible MVP women
4 lost to follow-up
14 moved out of Pittsburgh
4 pregnant
2 had pregnancy outcomes
within last 4 months
19 eligible for MVP II study visit
3 withdrawals
MVP II study (n=16)
Figure 1. Flowchart of the study population
Inclusion criteria for this study included: 1) prior participation in the MVP study; 2) at least 4 months since last pregnancy outcome; and 3) at least 1 to 5 years since index delivery. The participants were excluded if they: 1) were currently pregnant; 2) moved out of Pittsburgh area; or 3) were lost to follow-up. Thus, 19 women remained eligible for the MVP II study of which 3 withdrew from the study, leaving 16 women in the final evaluation (Figure 1). MVP II participants thus included a total of 16 healthy women, age 23-37 years, currently non-smoking, and with up to 2 additional pregnancies since their indexdelivery. All participants signed an informed consent document approved by the University of Pittsburgh Institutional Review Board.The visit included questionnaires to access pregnancy-related factors, physical measurements, and B-mode carotid ultrasound scans, performed by the research staff. Study visits were conducted between September 2014 and March 2015.
2.2 Ultrasound Assessment of the Common Carotid Artery
Figure 2. Ultrasound Image of CCA
Bilateral images of the CCA were obtained by a certified vascular sonographer via B-mode ultrasound using an Acuson Cypress portable ultrasound machine (Siemens Medical Solutions, Malvern, PA) equipped with a 7L3 linear transducer. Images were taken from the near and far walls of the distal CCA (1 cm proximal to the carotid bulb) and all images were read centrally at the Ultrasound Research Laboratory (University of Pittsburgh, Pittsburgh, PA). CCA IMT measures were electronically traced between the lumen-intima interface and the media-adventitia interface across the 1 cm segment using a semi-automated reading software (AMS system developed in Sweden by Dr. Thomas Gustavsson).1 The mean of the near and far wall IMT measurements from the left and right CCA comprises the average CCA IMT. The CCA IAD was measured from the same 1 cm CCA segment as the average distance between the adventitial-medial interface on the near wall and the medial-adventitial interface on the far wall (Figure 2).Reproducibility of CCA IMT measures was good to excellent with an intra-class correlation coefficient within sonographer of 0.85 and within reader of > 0.96. These scanning and reading protocols have been used in numerous studies.2-4
2.3 Pregnancy History and CVD Risk Factors
Study Forms. At the second postpartum study visit, participants completed a self-administered interval health history form with information on smoking, diabetes, health conditions, medications, breastfeeding, number of pregnancies, and contraceptive use. Participants reported whether they were currently breastfeeding and the time (in months) they breastfed each of their babies. Cumulative breastfeeding was calculated as a sum of total time (in months) of breastfeeding by each participant. Participants then completed a self-administered pregnancy outcomes form for each subsequent pregnancy since the last MVP visit including information such asoutcome of pregnancy, date of outcome, gestational age, birth weight and length, complications, and duration of breastfeeding.
Physical Measures. Research staff palpated the right radial pulse for 30 seconds and then measured blood pressure in that arm using a mercury sphygmomanometer after the participants rested for 5 minutes in a quiet room. Three measurements were taken according to a standardized protocol, and the average of the last two measures was used for the analysis. Research staff then weighed the participants on a standard balance scale twice, and the average of the readings was used for the analysis. Lastly, the research staff took two measurements each of the waist and the hip circumference with a tape measure according to a standardized protocol, and the average of each was used to calculate the waist-to-hip ratio.
Data Management Tool.Data on physical measures and from study forms were managed using REDCap (Research Electronic Data Capture) hosted at the University of Pittsburgh.11REDCap is a secure, web-based application designed to support data capture for research studies.11
Biochemical Assays. A 30 ml venous blood sample was collected from each participant at the study visit. After collection, the samples were kept at room temperature for ~0.5 h before being centrifuged at 4ºC for 15 minutes at 1500 g. These fasting serum samples were delivered on dry ice to the Heinz Nutrition Laboratory (University of Pittsburgh Graduate School of Public Health, Pittsburgh, PA) where assays were performed. Standard laboratory procedures were used to determine the blood glucose,5total cholesterol,6 high density lipoprotein (HDL-c),7 low density lipoprotein (LDL-c),8 and triglyceride9 levels. Insulin was measured using standard radio-immune assay (Linco Research, St. Charles, MO). HOMA-IR, a measure of insulin resistance, was calculated as (glucose x insulin)/405 for the purposes of analysis.10 High-sensitivity C-reactive protein (hsCRP) was measured with an enzyme-linked immunoassay (Alpha Diagnostics International, Inc. San Antonio, TX).
2.4 Power calculation
A statistical power analyses was performed to estimate the smallest detectable difference in vascular outcomes between the first and second postpartum visits, based on results from the MVP study (n=43). The mean standard deviation of differences in CCA IAD ranged from 0.16 to 0.67 mm and the mean standard deviation of differences in CCA IMT ranged from 0.02 to 0.09 mm between the various time-points of the MVP study12. Using a two-sided two-sample paired t-test for 16 participants with an alpha of 0.05 and power of 80%, the smallest detectable difference in CCA IAD was calculatedto bein the range of 0.112 to 0.469 mm and the smallest detectable difference in CCA IMT was calculated to be in the range of 0.014 to 0.063 mm. Since the number of participants in our study is very small, the detectable effect sizes for statistical significance for each of the vascular outcomes are quite large. Thus, this study can be seen as a pilot study to determine effect sizes for sample calculations for future studies.