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      Interaction of body mass index and hemoglobin concentration on blood pressure among pregnant women in Guangxi, China

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          Abstract

          Background

          Body mass index (BMI) and hemoglobin (Hb) are positively associated with hypertensive disorders among pregnant women. The aim of this study was to estimate a potential interaction between high BMI and high Hb concentrations on systolic blood pressure (SBP) and diastolic blood pressure (DBP) in pregnancy.

          Methods

          We recruited 4497 single-birth women aged 18–43 years who received routine antenatal care at three hospitals of Guigang, Guangxi, China, from December 2007 to January 2011. Of 4497 participants, 3472 women were in the first trimester, with following up, 2986 women and 2261 women were left in the second and third trimester, respectively. Clinical data were derived from medical records of each woman. We used multivariable linear regression, by trimesters of pregnancy, to evaluate the associations of high BMI and high Hb concentrations with SBP and DBP according to cross-sectional design.

          Results

          In multivariable analyses, BMI was positively associated with SBP throughout all trimesters, but the corresponding association for Hb concentrations only in the first trimester, whereas both BMI and Hb concentrations were positively associated with DBP in the first and third trimesters. After full adjustment for confounding, the average differences in SBP and DBP comparing women with high BMI and high Hb to those with non-high BMI and non-high Hb were 2.9 mmHg (95% CI: 0.8 to 5.0 mmHg) and 3.9 mmHg (95% CI: 1.5 to 6.3 mmHg) in the first trimester, 2.6 mmHg (95% CI: 0.4 to 4.8 mmHg) and 1.5 mmHg (95% CI: -1.3 to 4.3 mmHg) in the second trimester, and 4.8 mmHg (95% CI: 2.3 to 7.4 mmHg) and 5.7 mmHg (95% CI: 3.2 to 8.3 mmHg) in the third trimester, respectively. With respect to the interaction, significant combined effects between high BMI and high Hb were confirmed on SBP ( P = 0.02) and DBP ( P = 0.004) in the third trimester, and the amount of interaction on SBP and DBP were 2.0 mmHg (95% CI: 0.1 to 3.9 mmHg) and 2.3 mmHg (95% CI: 0.4 to 4.3 mmHg), respectively.

          Conclusion

          Our findings suggest that high BMI and high Hb concentrations may have a synergistic effect on blood pressure in late stage of pregnancy.

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          Most cited references30

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          Maternal body mass index and the risk of preeclampsia: a systematic overview.

          Maternal obesity, both in itself and as part of the insulin resistance syndrome, is an important risk factor for the development of preeclampsia. Accurately quantifying the relation between prepregnancy maternal body mass index and the risk of preeclampsia may better identify those at highest risk. We performed a systematic overview of the literature to determine the association between prepregnancy body mass index and the risk of preeclampsia. Two reviewers independently retrieved all relevant English language cohort studies through a systematic search of Medline and Embase between 1980 and June 2002. Study data were abstracted in a similar fashion. For each study, the risk ratio of preeclampsia was calculated by comparing the risk of preeclampsia among women with the highest body mass index with those with the lowest. We identified thirteen cohort studies, comprising nearly 1.4 million women. The risk of preeclampsia typically doubled with each 5-7 kg/m2 increase in prepregnancy body mass index. This relation persisted in studies that excluded women with chronic hypertension, diabetes mellitus or multiple gestations, or after adjustment for other confounders. Most observational studies demonstrate a consistently strong positive association between maternal prepregnancy body mass index and the risk of preeclampsia. Increasing obesity in developed countries is likely to increase the occurrence of preeclampsia. Consideration should be given to the potential benefits of prepregnancy weight reduction programs.
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            Estimating interaction on an additive scale between continuous determinants in a logistic regression model.

            To determine the presence of interaction in epidemiologic research, typically a product term is added to the regression model. In linear regression, the regression coefficient of the product term reflects interaction as departure from additivity. However, in logistic regression it refers to interaction as departure from multiplicativity. Rothman has argued that interaction estimated as departure from additivity better reflects biologic interaction. So far, literature on estimating interaction on an additive scale using logistic regression only focused on dichotomous determinants. The objective of the present study was to provide the methods to estimate interaction between continuous determinants and to illustrate these methods with a clinical example. and results From the existing literature we derived the formulas to quantify interaction as departure from additivity between one continuous and one dichotomous determinant and between two continuous determinants using logistic regression. Bootstrapping was used to calculate the corresponding confidence intervals. To illustrate the theory with an empirical example, data from the Utrecht Health Project were used, with age and body mass index as risk factors for elevated diastolic blood pressure. The methods and formulas presented in this article are intended to assist epidemiologists to calculate interaction on an additive scale between two variables on a certain outcome. The proposed methods are included in a spreadsheet which is freely available at: http://www.juliuscenter.nl/additive-interaction.xls.
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              Hyperglycaemia and Adverse Pregnancy Outcome (HAPO) Study: associations with maternal body mass index.

              (2010)
              To determine whether higher maternal body mass index (BMI), independent of maternal glycaemia, is associated with adverse pregnancy outcomes. Observational cohort study. Fifteen centres in nine countries. Eligible pregnant women. A 75-g 2-hour oral glucose tolerance test (OGTT) was performed between 24 and 32 weeks of gestation in all participants. Maternal BMI was calculated from height and weight measured at the OGTT. Fetal adiposity was assessed using skinfold measurements and percentage of body fat was calculated. Associations between maternal BMI and pregnancy outcomes were assessed using multiple logistic regression analyses, with adjustment for potential confounders. Predefined primary outcomes were birthweight >90th percentile, primary caesarean section, clinical neonatal hypoglycaemia and cord serum C-peptide >90th percentile. Secondary outcomes included pre-eclampsia, preterm delivery (before 37 weeks) and percentage of body fat >90th percentile. Among 23 316 blinded participants, with control for maternal glycaemia and other potential confounders, higher maternal BMI was associated (odds ratio [95% confidence interval] for highest {> or =42.0 kg/m(2)} versus lowest { 90th percentile (3.52 [2.48-5.00]) and percentage of body fat >90th percentile (3.28 [2.28-4.71]), caesarean section (2.23 [1.66-2.99]), cord C-peptide >90th percentile (2.33 [1.58-3.43]) and pre-eclampsia (14.14 [9.44-21.17]). Preterm delivery was less frequent with higher BMI (0.48 [0.31-0.74]). Associations with fetal size tended to plateau in the highest maternal BMI categories. Higher maternal BMI, independent of maternal glycaemia, is strongly associated with increased frequency of pregnancy complications, in particular those related to excess fetal growth and adiposity and to pre-eclampsia.
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                Author and article information

                Contributors
                Journal
                BMC Public Health
                BMC Public Health
                BMC Public Health
                BioMed Central
                1471-2458
                2014
                20 May 2014
                : 14
                : 474
                Affiliations
                [1 ]Department of Epidemiology, Guangxi Medical University School of Public Health, 22 Shuangyong Road, Nanning, Guangxi 530021, China
                [2 ]Department of Pediatrics, Nanning Maternal and Child Health Hospital, Nanning, China
                [3 ]Department of Comprehensive Laboratory, Guigang Entry-Exit Inspection and Quarantine Bureau, Guigang, China
                Article
                1471-2458-14-474
                10.1186/1471-2458-14-474
                4030466
                c096f76a-2c32-44c4-b897-b0ce7af8661c
                Copyright © 2014 Zhong et al.; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.

                History
                : 14 May 2013
                : 6 May 2014
                Categories
                Research Article

                Public health
                body mass index,hemoglobin,blood pressure,interaction,pregnancy
                Public health
                body mass index, hemoglobin, blood pressure, interaction, pregnancy

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