Physiology of blood pressure relevant to managing hypertension in pregnancy

Purpose: Pregnancy causes physiological changes in maternal organ systems, and blood pressure (BP) is one of the variables affected. This review is focusing on the physiology of BP relevant to the management of hypertension in pregnancy.

Materials and methods: A detailed literature search was performed using electronic databases (including WorldCat, PubMed, MEDLINE, Google Scholar) to retrieve and review reports related to physiology of BP in pregnancy.

Results: During pregnancy, there is vasodilation caused by mediators such as increased levels of progesterone and nitric oxide. The vasodilation leads to a reduction in vascular resistance, BP, and renal blood flow. In compensation, the following postulated events occur: activation of renin-angiotensin-aldosterone axis, resetting of osmotic threshold for thirst, and an increase in the production of vasopressin. Sodium and water conservation ensue to increase the total body water, end-diastolic volume, cardiac output, and BP. The increase in cardiac output incompletely compensates for the decreased vascular resistance, and BP therefore decreases in midpregnancy and returns to prepregnancy level toward term.

Conclusions: An understanding of the physiological changes in BP is essential for appropriate management of pregnancy-related hypertension.     

Inter-arm blood pressure differences in pregnant women

Objective  To determine the prevalence of blood pressure inter-arm difference (IAD) in early pregnancy and to investigate its possible association with maternal characteristics.
Design  A cross-sectional observational study.
Setting  Routine antenatal visit in a university hospital.
Population  A total of 5435 pregnant women at 11–14 weeks of gestation.
Methods  Blood pressure was taken from both arms simultaneously with a validated automated device.
Main outcome measures  The presence of inter-arm blood pressure difference of 10 mmHg or more.
Results  The IAD in systolic and diastolic blood pressure was 10 mmHg or more in 8.3 and 2.3% of the women, respectively. Systolic IAD was found to be significantly related to systolic blood pressure and pulse pressure, and diastolic IAD was found to be significantly related to maternal age, diastolic blood pressure and pulse pressure. The systolic and diastolic IAD were higher in the hypertensive group compared with the normotensive group and absolute IAD increased with increasing blood pressure. About 31.0 and 23.9% of cases of hypertension would have been underreported if the left arm and the right arm were used, respectively, in measuring the blood pressure.
Conclusions  There is a blood pressure IAD in a significant proportion of the pregnant population, and its prevalence increases with increasing blood pressure. By measuring blood pressure only on one arm, there is a one in three chance of underreporting hypertension. Therefore, it would be prudent that during the booking visit blood pressure should be taken in both arms and thus provide guidance for subsequent blood pressure measurements during the course of pregnancy.     

The importance of cuff width in measurement of blood pressure in pregnancy

Blood pressure was measured indirectly in 218 normotensive primigravidas with arm circumferences ranging from 21.7 to 36.1 cm using three standard blood pressure cuffs. It was found that the medical profession's lack of awareness as to the proper use of cuffs in prenatal care may involve 40% of the patients — 20% of these have a small arm circumference, will not show a true blood pressure reading, and may fail to get the proper treatment. On the other hand, 20% of these pateints who have a rather large arm circumference, may be grouped among those who need special care and attention, and may be given unnecessary treatment — a fact which may bring about clinical complications, unnecessary expense, incorrect statistical data and a misleading demographic impact.     

Tissue differences in DNA methylation changes at AHRR in full term low birth weight in maternal blood,placenta and cord blood in Chinese

IntroductionVery few study addressed the relationship between Aryl-hydrocarbon receptor repressor (AHRR) DNA methylation and low birth weight, especially in multiple tissues of mother-infant pairs. In this study, we aimed to investigate AHRR DNA methylation modification in cord blood, placenta and maternal blood between full term low birth weight (FT-LBW) and full term normal birth weight (FT-NBW) newborns.MethodsWe enrolled 90 FT-LBW and 90 FT-NBW mother-infant pairs, of which all placenta and cord blood samples were collected while 45 maternal blood samples of each group were collected. We measured AHRR DNA methylation (Chr5: 373013–373606) using Sequenom MassARRAY, and assessed associations between AHRR DNA methylation and FT-LBW using logistic regression adjusting for maternal age, education, family income, delivery mode, and passive smoking.ResultsFT-LBW babies had 3% lower methylation at Chr5: 373378 (CpG 13) in cord blood, and 4–9% higher methylation levels at Chr5: 373315, 373378, 373423, 373476 and 373490/373494 (CpG 10; 13; 15; 16; 17/18 respectively) in maternal blood, comparing with FT-NBW. The methylation of Chr5: 373378 (CpG 13) remained significant association with FT-LBW both in cord blood (OR = 0.90; 95% CI: 0.82, 0.98) and maternal blood (OR = 1.14; 95% CI: 1.04, 1.25) further adjusting for each other in the same model. We observed no significant difference at any CpG sites in placenta.DiscussionAHRR DNA methylation of cord and maternal blood might be independently associated with FT-LBW in different ways.     

Significance of high-normal blood pressure during early second trimester for predicting the onset of hypertensive disorders in pregnancy

Objective: The aim of this study was to determine the predictive value of high-normal blood pressure (HNBP) during the early second trimester for hypertensive disorders in pregnancy, including gestational hypertension (GH) and preeclampsia (PE). Methods: This was a retrospective single-center cohort study of 2143 singleton pregnant women. The association of HNBP, ranging from 130/85 to 139/89 mmHg between 14 and 19 weeks of gestation, with the development of hypertensive disorders was assessed by multivariable logistic regression analyses. Results: In a cohort of 2102 pregnant women, 93 (4.4%) pregnancies had HNBP during early second trimester. Pregnant women with HNBP more frequently developed hypertensive disorders than normotensive women (20.4% vs. 8.2%, p < 0.001). HNBP was significantly associated with the development of GH (adjusted odds ratio (aOR): 1.81; 95% confidence interval (CI): 1.16–3.25, p = 0.015) and PE (aOR: 6.05; 95% CI: 3.46–12.6, p = 0.013) after adjustment for confounders. Conclusion: HNBP during the early second trimester is an independent risk factor for both GH and PE.     

Dietary factors and cancers of breast, endometrium, and ovary: Strategies for modifying fat intake in African American women

Modification of dietary fat and fiber could help prevent cancers of the breast, endometrium, and ovary that are prevalent in African-American women. Dietary intervention programs aimed at reducing fat intake have had mixed results in this population. The transtheoretic model is proposed for achieving dietary change. Strategies for changing health behaviors in African-American women include heightening sensitivity to cultural values among health educators and the use of multiple strategies to reinforce messages. To stimulate healthier eating, it is important to incorporate the distinct habitual eating patterns into innovative intervention methods, using effective behavioral change methods. (Am J Obstet Gynecol 1997;176:S255-64.)     

Variation of DNA methylation in candidate age-related targets on the mitochondrial-telomere axis in cord blood and placenta

Background

Epigenetics is tissue-specific and potentially even cell-specific, but little information is available from human reproductive studies about the concordance of DNA methylation patterns in cord blood and placenta, as well as within-placenta variations. We evaluated methylation levels at promoter regions of candidate genes in biological ageing pathways (SIRT1, TP53, PPARG, PPARGC1A, and TFAM), a subtelomeric region (D4Z4) and the mitochondrial genome (MT-RNR1, D-loop).

Methods

Ninety individuals were randomly chosen from the ENVIRONAGE birth cohort to evaluate methylation concordance between cord blood and placenta using highly quantitative bisulfite-PCR pyrosequencing. In a subset of nineteen individuals, a more extensive sampling scheme was performed to examine within-placenta variation.

Results

The DNA methylation levels of the subtelomeric region and mitochondrial genome showed concordance between cord blood and placenta with correlation coefficients ranging from r = 0.31 to 0.43, p ≤ 0.005, and also between the maternal and foetal sides of placental tissue (r = 0.53 to 0.72, p ≤ 0.05). For the majority of targets, an agreement in methylation levels between four foetal biopsies was found (with intra-class correlation coefficients ranging from 0.16 to 0.72), indicating small within-placenta variation.

Conclusions

The methylation levels of the subtelomeric region (D4Z4) and mitochondrial genome (MT-RNR1, D-loop) showed concordance between cord blood and placenta, suggesting a common epigenetic signature of these targets between tissues. Concordance was lacking between the other genes that were studied. In placental tissue, methylation patterns of most targets on the mitochondrial-telomere axis were not strongly influenced by sample location.     

Effects of raloxifene therapy on plasma renin and aldosterone levels and blood pressure in postmenopausal women

Objective.?Blood pressure, which generally increases after menopause, is one of the best tools to characterize cardiovascular disease. The renin–aldosterone system plays a role in determining cardiovascular risk and the role of estrogen in the regulation of angiotensinogen gene expression and serum levels is well known. Raloxifene can induce endothelium-dependent vasodilation without affecting endothelium-independent vasorelaxation. The aim of the study was to investigate the effects of raloxifene on the renin–aldosterone system and blood pressure in postmenopausal women.

Designs.?Forty women, 54–59 years of age, in physiological menopause for 6 months to 4 years, were enrolled in the study and treated with raloxifene 60 mg/day for 6 months. All had blood pressure less than 130/85 mm Hg at the start of the study. The women were divided into two groups: the first (group A; 20 women) with normal blood pressure and the second (group B; 20 women) with previous high blood pressure treated with antihypertensive drugs, not angiotensin-converting enzyme inhibitors or angiotensin receptor blockers.

Results.?No significant changes in plasma renin activity (PRA) or plasma concentrations of aldosterone were observed between the two groups after 6 months of raloxifene use. There was a slight reduction in PRA (11±4% for group A and 13±5% for group B) and in plasma levels of aldosterone (3.6±0.5% and 4.6±0.5%, respectively) with respect to basal values, but neither change was statistically significant.

Conclusions.?The results of the present study show that raloxifene at 60 mg/day dose is well tolerated and has no clinical impact on blood pressure, PRA or aldosterone in postmenopausal women.     

Effect of regular exercise on blood pressure in normotensive pregnant women. A randomized controlled trial

Objective: To evaluate the effect of regular exercise on maternal arterial blood pressure (BP) at rest and during uphill walking, in healthy former inactive pregnant women. Methods: A single-blind, single-center, randomized controlled trial including 61 out of 105 healthy, inactive nulliparous pregnant women, initially enrolled in a controlled trial studying the effect of 12 weeks of aerobic exercise (60 min 2/week) on maternal weight gain. Primary outcome was the mean adjusted difference in change in resting systolic and diastolic BP from baseline to after intervention. Secondary outcome was the mean adjusted difference in change in systolic BP during uphill treadmill walking at critical power. Measurements were performed prior to the intervention (gestation week 17.6 ± 4.2) and after the intervention (gestation week 36.5 ± 0.9). Results: At baseline, resting systolic and diastolic BP was 115/66 ± 12/7 and 115/67 ± 10/9 mmHg in the exercise (n = 35) and control group (n = 26), respectively. After the intervention, resting systolic BP was 112 ± 8 mmHg in the exercise group and 119 ± 14 mmHg in the control group, giving a between-group difference of 7.5 mmHg (95% CI 1.5 to 12.6, p = 0.013). Diastolic BP was 71 ± 9 and 76 ± 8 mmHg, with a between-group difference of 3.9 mmHg (95% CI ?0.07 to 7.8, p = 0.054). During uphill treadmill walking at critical power, the between-group difference in systolic and diastolic BP was 5.9 mmHg (95% CI ?4.4 to 16.1, p = 0.254) and 5.5 mmHg (95% CI –0.2 to 11.1, p = 0.059), respectively. Conclusions: Aerobic exercise reduced resting systolic BP in healthy former inactive pregnant women.