Original Article
Fetal and maternal angiotensin (1-7) are associated with preterm birth You-Peng Chen a,, Yong-Ping Lu a,, Jian Li c, Zhi-Wei Liu a, Wen-Jing Chen b, Xu-Jing Liang a, Xin Chen d, Wang-Rong Wen b, Xiao-Min Xiao d, Christoph Reichetzeder e, and Berthold Hocher a,e
Background: Recent studies show that preterm birth is associated with hypertension in later life. The renin–angiotensin system (RAS) during pregnancy influences fetal growth and development. In the current study, we investigated the impact of fetal as well as maternal angiotensin (1-7) [Ang (1-7)] and angiotensin II (Ang II) plasma concentrations on the risk of preterm birth. Methods: Three hundred and nine pregnant women were prospectively included into the study. The pregnant women were divided into two groups, for example, preterm birth of lower than 37 gestational weeks (n ¼ 17) and full-term birth of 37 gestational weeks or more (n ¼ 292). Maternal and neonatal plasma Ang (1-7) and Ang II concentrations were analyzed at birth from maternal venous blood and umbilical cord blood, respectively. Risk factors for premature birth were determined by multiple logistic regression analysis. Results: Fetal and maternal plasma Ang (1-7) concentrations in the preterm group were lower than those of the term group fetal Ang (1-7) preterm birth: 486.15 337.34 ng/l and fetal Ang (1-7) term birth: 833.84 698.12 ng/l and maternal Ang (1-7) preterm birth: 399.86 218.93 ng/l; maternal Ang (1-7) term birth: 710.34 598.22 ng/l. Multiple logistic regression analysis considering confounding factors revealed that preeclampsia (P < 0.001), premature rupture of membranes (P ¼ 0.001), lower concentration of maternal Ang (1-7) (P ¼ 0.013) and fetal plasma Ang (1-7) (P ¼ 0.032) were independently associated with preterm birth. We could furthermore demonstrate that the maternal Ang (1-7)/Ang II ratio is independently associated with gestational hypertension or preeclampsia, factors causing preterm birth. Conclusions: Lower concentrations of maternal and fetal Ang (1-7) are independently associated with preterm birth – a risk factor of hypertension in later life. Keywords: angiotensin (1-7), angiotensin II, cardiovascular disease, fetal programming, intrauterine fetal growth, pregnancy, preterm delivery
INTRODUCTION
U
ntil recently, fetal programming of adult disease was solely attributed to intrauterine growth restriction (IUGR) and a ‘deprived’ intrauterine environment, leading to low birth weight, which is the most used surrogate parameter of fetal programming [1–4]. As many of these epidemiologic studies were based on old birth records, the definition of low birth weight was also different [5,6]. Therefore, it is possible that a considerable amount of individuals included into these epidemiologic studies, which were performed without assessing gestational age, actually were preterm individuals and not small for gestational age or IUGR [7]. In a systematic literature review followed by a meta-analysis, De Jong et al. [8] demonstrated that preterm birth predicts higher blood pressure in later life. Their results indicate that individuals born preterm have a higher SBP in later life than infants born at term [8]. Pregnancy is a physiological condition characterized by a progressive increase of the different components of the renin–angiotensin system (RAS) [9–11]. Interestingly, although the RAS is up-regulated in pregnancy, blood pressure stays normal due to a progressive angiotensin II (Ang II) resistance [12–14]. This is at least partially due to a decrease of the AT1 receptor density [15,16]. Another reason is a marked up-regulation of the angiotensin-converting enzyme 2 (ACE2)–angiotensin (1-7) [Ang (1-7)–Mas receptor axis of the RAS during pregnancy, which acts counter-regulatory to the ACE –Ang II–Ang II type 1 receptor axis. ACE2 knockout mice, which are lacking the Ang (1-7)-generating enzyme, are characterized by a significantly higher blood pressure during pregnancy as compared to wild-type mice. In addition, ACE2 knockout Journal of Hypertension 2014, 32:1833–1841 a Department of Infectious Diseases, bDepartment of Laboratory Medicine, the first Affiliated Hospital of Jinan University, Guangzhou, cDepartment of Clinical Medicine, Medical College of Hunan Normal University, Changsha, dDepartment of Obstetrics and Gynecology, the first Affiliated Hospital of Jinan University, Guangzhou, China and eInstitute of Nutritional Science, University of Potsdam, Nuthetal, Potsdam, Germany
Correspondence to Professor Berthold Hocher, MD, PhD, Institute of Nutritional Science, University of Potsdam, D-14558 Nuthetal, Potsdam, Germany. E-mail: [email protected], http://www.uni-potsdam.de/eem
You-Peng Chen and Yong-Ping Lu contributed equally to the writing of this article.
Received 23 August 2013 Revised 28 April 2014 Accepted 28 April 2014
Abbreviations: Ang (1-7), angiotensin (1-7); Ang II, angiotensin II; RAS, renin–angiotensin system
J Hypertens 32:1833–1841 ß 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins. DOI:10.1097/HJH.0000000000000251
Journal of Hypertension
www.jhypertension.com
1833
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Chen et al.
mice give birth to growth-restricted offspring [17]. Responsible for the up-regulation of the ACE2–Ang (1-7) –Mas receptor axis are high circulating concentrations of estrogen and other reproductive hormones during pregnancy, shifting pathways of angiotensin peptide formation in a tissuespecific manner [18–20]. In this context it is noteworthy that renal and uterine expression and activity of the Ang (1-7)generating enzyme ACE2 are up-regulated and that nulliparous pregnant women show strongly elevated levels of Ang (1-7) in the third trimester of pregnancy compared to nonpregnant women [20–22]. These findings underline an important role of this peptide hormone during pregnancy. In humans, ACE2 and Ang (1-7) are generally colocalized in the utero-placental unit during gestation, suggesting an autocrine function of Ang (1-7) [23,24]. An influence of the Ang (1-7) –ACE2–mas receptor axis on blood pressure regulation during pregnancy was suggested, since reduced plasma Ang (1-7) levels were seen in preeclamptic women [25,26]. Taken together, the RAS contributes to blood pressure regulation during pregnancy, The RAS during pregnancy, however, also influences risk factors of preterm birth [24–27], and preterm birth has long-lasting consequences on the risk for cardiovascular diseases in later life such as hypertension. Thus, we want to test in the hypothesis that the RAS might determine gestational age. To address this question, we analyzed the relationship between Ang 1-7 and Ang II as key parts of the RAS and gestational age in a cohort of 309 Chinese pregnant ladies and their newborns.
MATERIAL AND METHODS Participants and data collection The study was a prospective observational study. The study was approved by the Ethics Committee of the Jinan University, Guangzhou, China. We invited a total of 340 Chinese women to participate, 31 refused to participate; finally 309 women who delivered their babies at the Obstetric Department of the First Affiliated Hospital of the Jinan University between August 2011 and December 2011 entered the study. Key inclusion criteria of the cohort were: ultrasound measurements done at the second trimester showed no structural anomalies of the fetus, singleton pregnancy, no alcohol/drug/smoking abuse during and before pregnancy, no hypertension before pregnancy, no diabetes mellitus before pregnancy, and no infectious diseases such as syphilis, HIV, viral hepatitis, cytomegalovirus, herpes simplex virus, and Toxoplasma gondii. After obtaining written informed consent, a structured medical history was taken. The following data were extracted into our database: age, BMI before pregnancy, gravidity, parity, history of preterm childbirth, history of abortion (including spontaneous abortion and medical abortion), and weight gain during pregnancy. We also documented pregnancy-related diseases such as preeclampsia (mild preeclampsia: SBP of 140–159 mmHg and/or DBP of 90–109 mmHg, measured over a period of 4–6 h after 20th week of gestation, and urinary total protein excretion of 300–1999 mg in 24 h or urine dipstick 1834
www.jhypertension.com
indicating 1þ of protein; severe preeclampsia: SBP 160 mmHg and/or DBP 110 mmHg, measured over a period of 4–6 h after 20th week of gestation, and urinary total protein of 2000 mg in 24 h or urine dipstick indicating 2þ of protein), gestational hypertension without proteinuria, gestational diabetes, placenta praevia, and premature rupture of membranes (defined as membrane rupture before labor). Biometric data of the newborn were also taken: gestational age, birth weight, birth height, head circumference, and APGAR score (The Apgar scale is determined by evaluating a newborn on five simple criteria: Appearance, Pulse, Grimace, Activity, Respiration) .
Sample collection, blood angiotensin (1-7) and angiotensin II assay Midwives collected maternal blood from a cubital vein in the delivery room or on the ward prior to birth, before the usage of oxytocin, or any other analgesics. Fetal blood was taken immediately after the cut of the umbilical cord. Blood was taken in EDTA tubes and centrifuged at 48C immediately after taking the blood, and plasma was frozen at 808C immediately after the centrifugation step. Time of taking blood from both the mother and the newborn was documented. Samples were processed immediately and were stored at 208C until analysis. Blood level of Ang (1-7) and Ang II were measured by ELISA [Human Angiotensin-II ELISA kit (no. GS-E11204) and angiotensin (1-7) ELISA kit (no. GS-E22605)] provided by Yan-Yu Chemical Reagants Co. Ltd., Shanghai, China. All measurements were done in duplicate. The mean value was calculated and used for the analysis. The detection range of the Ang (1-7) assay was 15–500 ng/l and that of the Ang II assay was 1.5–50 ng/ l. All samples were diluted five-fold before assayed. When the samples’ concentration exceeded the detection range of Ang (1-7) or Ang II, the samples were diluted 10-fold and assayed again. All blood samples were measured by experienced staff in a certified hospital laboratory of the university.
Statistical analysis Data were analyzed with SPSS version 17.0. Results of quantitative data were expressed as arithmetic mean SD. Student’s unpaired t-test and analysis of variance (ANOVA) was used for comparison of continuous variables between groups. Pearson’s chi-square test was used for testing qualitative data, if 1 theoretical frequency < 5 (1 T < 5). The P-value was determined by continuity correction. A P-value of less than 0.05 was considered significant difference. Factors [maternal age, BMI before pregnancy, gravidity, parity, primipara, history of abortion, gestational diabetes, gestational hypertension, preeclampsia, premature rupture of membranes, fetal distress, child sex, maternal Ang (1-7), maternal Ang II, fetal Ang (1-7), fetal Ang I that might affect preterm birth were analyzed by univariate logistic regression. A P value 0.05 or less was considered as risk factor for preterm birth in this first step of analysis. If factors showed a significant association in the first univariate logistic regression analysis, these factors were used thereafter in different models of multiple logistic regression Volume 32 Number 9 September 2014
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Fetal and maternal angiotensin (1-7) associated with preterm birth TABLE 1. Detailed description data of the entire study cohort (n ¼ 309) Variable Maternal age (years) Maternal height (cm) BMI before pregnancy (kg/m2) Gravidity Parity Primipara [n (%)] History of preterm [n (%)] History of abortion [n (%)] Gestational diabetes [n (%)] Gestational hypertension [n (%)] Preeclampsia during pregnancy [n (%)] Placenta praevia [n (%)] Premature rupture of membranes [n (%)] Labor way, vaginal/c-section [n (%)] Child birth weight (g) Child sex, male/female [n (%)] APGAR score 1 min 5 min 10 min Maternal Ang (1-7) (ng/l) Maternal Ang II (ng/l) Maternal Ang (1-7)/Ang II Fetal Ang (1-7) (ng/l) Fetal Ang II (ng/l) Fetal Ang (1-7)/Ang II ratio
Mean SD/n (%) 28.44 3.81 159.84 4.58 20.27 2.51 1.74 1.14 1.18 0.43 243 (81.88) 1 (0.3) 89 (28.80) 65 (21.04) 16 (5.18) 12 (3.88) 3 (0.97) 44 (14.29) 106 (34.30)/203(65.70) 3255.00 412.49 162 (52.43)/147(47.57) 8.91 0.65 9.95 0.25 9.99 0.11 693.26 58.91 71.31 59.72 9.72 2.79 814.7 687.52 82.84 68.00 9.84 3.08
Ang, angiotensin.
analysis. The following confounding factors were included into the models testing factors for preterm birth: 1. Gestational hypertension, preterm brane, maternal Ang (1-7) tertiles 2. Preeclampsia, preterm rupture maternal Ang (1-7) tertiles 3. Gestational hypertension, preterm brane, fetal Ang (1-7) tertiles 4. Preeclampsia, preterm rupture of Ang (1-7) tertiles
rupture of memof
membrane,
rupture of memmembrane, fetal
Additionally, factors [maternal age, BMI before pregnancy, maternal Ang (1-7) tertiles, maternal Ang II tertiles,
fetal Ang (1-7) tertiles, fetal Ang II tertiles] that might affect gestational hypertension and preeclampsia were analyzed. Groups were compared by t-test. In a second step, we performed a multiple logistic regression for gestational hypertension/preeclampsia to consider confounding. In a similar manner, we analyzed factors that might affect birth weight.
RESULTS Description of the cohort Descriptive data of the study population are given in Table 1. The study population represents a typical Chinese birth cohort with respect to key characteristics like maternal age, BMI before pregnancy, gravidity, parity, labor way, offspring birth weight, and sex (for more details, see Table 1). When comparing women giving birth preterm with those giving birth at term, data concerning maternal height, BMI before pregnancy, gravidity, parity, primipara, history of previous preterm childbirth, history of abortion, gestational diabetes, and placenta praevia were not different between the groups (P > 0.05). Mothers having preterm birth showed a significantly higher incidence of gestational hypertension, preeclampsia, and premature rupture of membranes as compared to the control group (P < 0.01 in all cases). Maternal weight gain during pregnancy in the preterm birth group was much lower as compared to cases of term birth group (P ¼ 0.008, Table 2). Comparing offspring of women giving preterm birth with those giving birth at term revealed that gestational age was 248.12 8.88 days only in the preterm group and 276.63 6.89 days in the term group (P < 0.01). Birth weight in the preterm group was 2477.65 523.90 g and in the term group it was 3300.26 357.27 g (P < 0.01) (for more details, see Table 3).
Maternal/fetal angiotensin (1-7), angiotensin II and angiotensin (1-7)/angiotensin II ratio Concentrations of plasma Ang (1-7) and Ang II in maternal blood as well as in umbilical cord blood were significantly lower in the preterm delivery group as compared to the term delivery group (for details, see Table 4 and Fig. 1).
TABLE 2. Maternal data according to gestational age status (preterm versus full-term birth) Variable
Preterm group (n ¼ 17)
Full-term group (n ¼ 292)
t/x2
P-value
29.12 5.49 160.12 4.21 21.21 3.22 1.74 1.15 1.17 0.42 14 (82.35%) 0 (0%) 5 (29.41%) 35.45 1.27 13.19 3.95 2 (11.76%) 5 (29.41%) 5 (29.41%) 0 (0%) 9 (52.94%)
28.40 3.69 159.83 4.60 20.21 2.46 1.71 0.99 1.29 0.59 239 (81.85%) 1 (0.34%) 84 (28.77%) 39.46 0.96 16.10 4.56 63 (21.57%) 11 (3.77%) 7 (2.40%) 3 (1.03%) 45 (15.41%)
0.76 0.25 1.60 0.13 0.83 0 0 0.03 12.84 2.52 0.43 16.61 24.59 0 13.20
0.449 0.801 0.111 0.896 0.421 1.0 1.0 0.953
Fetal and maternal angiotensin (1-7) are associated with preterm birth You-Peng Chen a,, Yong-Ping Lu a,, Jian Li c, Zhi-Wei Liu a, Wen-Jing Chen b, Xu-Jing Liang a, Xin Chen d, Wang-Rong Wen b, Xiao-Min Xiao d, Christoph Reichetzeder e, and Berthold Hocher a,e
Background: Recent studies show that preterm birth is associated with hypertension in later life. The renin–angiotensin system (RAS) during pregnancy influences fetal growth and development. In the current study, we investigated the impact of fetal as well as maternal angiotensin (1-7) [Ang (1-7)] and angiotensin II (Ang II) plasma concentrations on the risk of preterm birth. Methods: Three hundred and nine pregnant women were prospectively included into the study. The pregnant women were divided into two groups, for example, preterm birth of lower than 37 gestational weeks (n ¼ 17) and full-term birth of 37 gestational weeks or more (n ¼ 292). Maternal and neonatal plasma Ang (1-7) and Ang II concentrations were analyzed at birth from maternal venous blood and umbilical cord blood, respectively. Risk factors for premature birth were determined by multiple logistic regression analysis. Results: Fetal and maternal plasma Ang (1-7) concentrations in the preterm group were lower than those of the term group fetal Ang (1-7) preterm birth: 486.15 337.34 ng/l and fetal Ang (1-7) term birth: 833.84 698.12 ng/l and maternal Ang (1-7) preterm birth: 399.86 218.93 ng/l; maternal Ang (1-7) term birth: 710.34 598.22 ng/l. Multiple logistic regression analysis considering confounding factors revealed that preeclampsia (P < 0.001), premature rupture of membranes (P ¼ 0.001), lower concentration of maternal Ang (1-7) (P ¼ 0.013) and fetal plasma Ang (1-7) (P ¼ 0.032) were independently associated with preterm birth. We could furthermore demonstrate that the maternal Ang (1-7)/Ang II ratio is independently associated with gestational hypertension or preeclampsia, factors causing preterm birth. Conclusions: Lower concentrations of maternal and fetal Ang (1-7) are independently associated with preterm birth – a risk factor of hypertension in later life. Keywords: angiotensin (1-7), angiotensin II, cardiovascular disease, fetal programming, intrauterine fetal growth, pregnancy, preterm delivery
INTRODUCTION
U
ntil recently, fetal programming of adult disease was solely attributed to intrauterine growth restriction (IUGR) and a ‘deprived’ intrauterine environment, leading to low birth weight, which is the most used surrogate parameter of fetal programming [1–4]. As many of these epidemiologic studies were based on old birth records, the definition of low birth weight was also different [5,6]. Therefore, it is possible that a considerable amount of individuals included into these epidemiologic studies, which were performed without assessing gestational age, actually were preterm individuals and not small for gestational age or IUGR [7]. In a systematic literature review followed by a meta-analysis, De Jong et al. [8] demonstrated that preterm birth predicts higher blood pressure in later life. Their results indicate that individuals born preterm have a higher SBP in later life than infants born at term [8]. Pregnancy is a physiological condition characterized by a progressive increase of the different components of the renin–angiotensin system (RAS) [9–11]. Interestingly, although the RAS is up-regulated in pregnancy, blood pressure stays normal due to a progressive angiotensin II (Ang II) resistance [12–14]. This is at least partially due to a decrease of the AT1 receptor density [15,16]. Another reason is a marked up-regulation of the angiotensin-converting enzyme 2 (ACE2)–angiotensin (1-7) [Ang (1-7)–Mas receptor axis of the RAS during pregnancy, which acts counter-regulatory to the ACE –Ang II–Ang II type 1 receptor axis. ACE2 knockout mice, which are lacking the Ang (1-7)-generating enzyme, are characterized by a significantly higher blood pressure during pregnancy as compared to wild-type mice. In addition, ACE2 knockout Journal of Hypertension 2014, 32:1833–1841 a Department of Infectious Diseases, bDepartment of Laboratory Medicine, the first Affiliated Hospital of Jinan University, Guangzhou, cDepartment of Clinical Medicine, Medical College of Hunan Normal University, Changsha, dDepartment of Obstetrics and Gynecology, the first Affiliated Hospital of Jinan University, Guangzhou, China and eInstitute of Nutritional Science, University of Potsdam, Nuthetal, Potsdam, Germany
Correspondence to Professor Berthold Hocher, MD, PhD, Institute of Nutritional Science, University of Potsdam, D-14558 Nuthetal, Potsdam, Germany. E-mail: [email protected], http://www.uni-potsdam.de/eem
You-Peng Chen and Yong-Ping Lu contributed equally to the writing of this article.
Received 23 August 2013 Revised 28 April 2014 Accepted 28 April 2014
Abbreviations: Ang (1-7), angiotensin (1-7); Ang II, angiotensin II; RAS, renin–angiotensin system
J Hypertens 32:1833–1841 ß 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins. DOI:10.1097/HJH.0000000000000251
Journal of Hypertension
www.jhypertension.com
1833
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Chen et al.
mice give birth to growth-restricted offspring [17]. Responsible for the up-regulation of the ACE2–Ang (1-7) –Mas receptor axis are high circulating concentrations of estrogen and other reproductive hormones during pregnancy, shifting pathways of angiotensin peptide formation in a tissuespecific manner [18–20]. In this context it is noteworthy that renal and uterine expression and activity of the Ang (1-7)generating enzyme ACE2 are up-regulated and that nulliparous pregnant women show strongly elevated levels of Ang (1-7) in the third trimester of pregnancy compared to nonpregnant women [20–22]. These findings underline an important role of this peptide hormone during pregnancy. In humans, ACE2 and Ang (1-7) are generally colocalized in the utero-placental unit during gestation, suggesting an autocrine function of Ang (1-7) [23,24]. An influence of the Ang (1-7) –ACE2–mas receptor axis on blood pressure regulation during pregnancy was suggested, since reduced plasma Ang (1-7) levels were seen in preeclamptic women [25,26]. Taken together, the RAS contributes to blood pressure regulation during pregnancy, The RAS during pregnancy, however, also influences risk factors of preterm birth [24–27], and preterm birth has long-lasting consequences on the risk for cardiovascular diseases in later life such as hypertension. Thus, we want to test in the hypothesis that the RAS might determine gestational age. To address this question, we analyzed the relationship between Ang 1-7 and Ang II as key parts of the RAS and gestational age in a cohort of 309 Chinese pregnant ladies and their newborns.
MATERIAL AND METHODS Participants and data collection The study was a prospective observational study. The study was approved by the Ethics Committee of the Jinan University, Guangzhou, China. We invited a total of 340 Chinese women to participate, 31 refused to participate; finally 309 women who delivered their babies at the Obstetric Department of the First Affiliated Hospital of the Jinan University between August 2011 and December 2011 entered the study. Key inclusion criteria of the cohort were: ultrasound measurements done at the second trimester showed no structural anomalies of the fetus, singleton pregnancy, no alcohol/drug/smoking abuse during and before pregnancy, no hypertension before pregnancy, no diabetes mellitus before pregnancy, and no infectious diseases such as syphilis, HIV, viral hepatitis, cytomegalovirus, herpes simplex virus, and Toxoplasma gondii. After obtaining written informed consent, a structured medical history was taken. The following data were extracted into our database: age, BMI before pregnancy, gravidity, parity, history of preterm childbirth, history of abortion (including spontaneous abortion and medical abortion), and weight gain during pregnancy. We also documented pregnancy-related diseases such as preeclampsia (mild preeclampsia: SBP of 140–159 mmHg and/or DBP of 90–109 mmHg, measured over a period of 4–6 h after 20th week of gestation, and urinary total protein excretion of 300–1999 mg in 24 h or urine dipstick 1834
www.jhypertension.com
indicating 1þ of protein; severe preeclampsia: SBP 160 mmHg and/or DBP 110 mmHg, measured over a period of 4–6 h after 20th week of gestation, and urinary total protein of 2000 mg in 24 h or urine dipstick indicating 2þ of protein), gestational hypertension without proteinuria, gestational diabetes, placenta praevia, and premature rupture of membranes (defined as membrane rupture before labor). Biometric data of the newborn were also taken: gestational age, birth weight, birth height, head circumference, and APGAR score (The Apgar scale is determined by evaluating a newborn on five simple criteria: Appearance, Pulse, Grimace, Activity, Respiration) .
Sample collection, blood angiotensin (1-7) and angiotensin II assay Midwives collected maternal blood from a cubital vein in the delivery room or on the ward prior to birth, before the usage of oxytocin, or any other analgesics. Fetal blood was taken immediately after the cut of the umbilical cord. Blood was taken in EDTA tubes and centrifuged at 48C immediately after taking the blood, and plasma was frozen at 808C immediately after the centrifugation step. Time of taking blood from both the mother and the newborn was documented. Samples were processed immediately and were stored at 208C until analysis. Blood level of Ang (1-7) and Ang II were measured by ELISA [Human Angiotensin-II ELISA kit (no. GS-E11204) and angiotensin (1-7) ELISA kit (no. GS-E22605)] provided by Yan-Yu Chemical Reagants Co. Ltd., Shanghai, China. All measurements were done in duplicate. The mean value was calculated and used for the analysis. The detection range of the Ang (1-7) assay was 15–500 ng/l and that of the Ang II assay was 1.5–50 ng/ l. All samples were diluted five-fold before assayed. When the samples’ concentration exceeded the detection range of Ang (1-7) or Ang II, the samples were diluted 10-fold and assayed again. All blood samples were measured by experienced staff in a certified hospital laboratory of the university.
Statistical analysis Data were analyzed with SPSS version 17.0. Results of quantitative data were expressed as arithmetic mean SD. Student’s unpaired t-test and analysis of variance (ANOVA) was used for comparison of continuous variables between groups. Pearson’s chi-square test was used for testing qualitative data, if 1 theoretical frequency < 5 (1 T < 5). The P-value was determined by continuity correction. A P-value of less than 0.05 was considered significant difference. Factors [maternal age, BMI before pregnancy, gravidity, parity, primipara, history of abortion, gestational diabetes, gestational hypertension, preeclampsia, premature rupture of membranes, fetal distress, child sex, maternal Ang (1-7), maternal Ang II, fetal Ang (1-7), fetal Ang I that might affect preterm birth were analyzed by univariate logistic regression. A P value 0.05 or less was considered as risk factor for preterm birth in this first step of analysis. If factors showed a significant association in the first univariate logistic regression analysis, these factors were used thereafter in different models of multiple logistic regression Volume 32 Number 9 September 2014
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Fetal and maternal angiotensin (1-7) associated with preterm birth TABLE 1. Detailed description data of the entire study cohort (n ¼ 309) Variable Maternal age (years) Maternal height (cm) BMI before pregnancy (kg/m2) Gravidity Parity Primipara [n (%)] History of preterm [n (%)] History of abortion [n (%)] Gestational diabetes [n (%)] Gestational hypertension [n (%)] Preeclampsia during pregnancy [n (%)] Placenta praevia [n (%)] Premature rupture of membranes [n (%)] Labor way, vaginal/c-section [n (%)] Child birth weight (g) Child sex, male/female [n (%)] APGAR score 1 min 5 min 10 min Maternal Ang (1-7) (ng/l) Maternal Ang II (ng/l) Maternal Ang (1-7)/Ang II Fetal Ang (1-7) (ng/l) Fetal Ang II (ng/l) Fetal Ang (1-7)/Ang II ratio
Mean SD/n (%) 28.44 3.81 159.84 4.58 20.27 2.51 1.74 1.14 1.18 0.43 243 (81.88) 1 (0.3) 89 (28.80) 65 (21.04) 16 (5.18) 12 (3.88) 3 (0.97) 44 (14.29) 106 (34.30)/203(65.70) 3255.00 412.49 162 (52.43)/147(47.57) 8.91 0.65 9.95 0.25 9.99 0.11 693.26 58.91 71.31 59.72 9.72 2.79 814.7 687.52 82.84 68.00 9.84 3.08
Ang, angiotensin.
analysis. The following confounding factors were included into the models testing factors for preterm birth: 1. Gestational hypertension, preterm brane, maternal Ang (1-7) tertiles 2. Preeclampsia, preterm rupture maternal Ang (1-7) tertiles 3. Gestational hypertension, preterm brane, fetal Ang (1-7) tertiles 4. Preeclampsia, preterm rupture of Ang (1-7) tertiles
rupture of memof
membrane,
rupture of memmembrane, fetal
Additionally, factors [maternal age, BMI before pregnancy, maternal Ang (1-7) tertiles, maternal Ang II tertiles,
fetal Ang (1-7) tertiles, fetal Ang II tertiles] that might affect gestational hypertension and preeclampsia were analyzed. Groups were compared by t-test. In a second step, we performed a multiple logistic regression for gestational hypertension/preeclampsia to consider confounding. In a similar manner, we analyzed factors that might affect birth weight.
RESULTS Description of the cohort Descriptive data of the study population are given in Table 1. The study population represents a typical Chinese birth cohort with respect to key characteristics like maternal age, BMI before pregnancy, gravidity, parity, labor way, offspring birth weight, and sex (for more details, see Table 1). When comparing women giving birth preterm with those giving birth at term, data concerning maternal height, BMI before pregnancy, gravidity, parity, primipara, history of previous preterm childbirth, history of abortion, gestational diabetes, and placenta praevia were not different between the groups (P > 0.05). Mothers having preterm birth showed a significantly higher incidence of gestational hypertension, preeclampsia, and premature rupture of membranes as compared to the control group (P < 0.01 in all cases). Maternal weight gain during pregnancy in the preterm birth group was much lower as compared to cases of term birth group (P ¼ 0.008, Table 2). Comparing offspring of women giving preterm birth with those giving birth at term revealed that gestational age was 248.12 8.88 days only in the preterm group and 276.63 6.89 days in the term group (P < 0.01). Birth weight in the preterm group was 2477.65 523.90 g and in the term group it was 3300.26 357.27 g (P < 0.01) (for more details, see Table 3).
Maternal/fetal angiotensin (1-7), angiotensin II and angiotensin (1-7)/angiotensin II ratio Concentrations of plasma Ang (1-7) and Ang II in maternal blood as well as in umbilical cord blood were significantly lower in the preterm delivery group as compared to the term delivery group (for details, see Table 4 and Fig. 1).
TABLE 2. Maternal data according to gestational age status (preterm versus full-term birth) Variable
Preterm group (n ¼ 17)
Full-term group (n ¼ 292)
t/x2
P-value
29.12 5.49 160.12 4.21 21.21 3.22 1.74 1.15 1.17 0.42 14 (82.35%) 0 (0%) 5 (29.41%) 35.45 1.27 13.19 3.95 2 (11.76%) 5 (29.41%) 5 (29.41%) 0 (0%) 9 (52.94%)
28.40 3.69 159.83 4.60 20.21 2.46 1.71 0.99 1.29 0.59 239 (81.85%) 1 (0.34%) 84 (28.77%) 39.46 0.96 16.10 4.56 63 (21.57%) 11 (3.77%) 7 (2.40%) 3 (1.03%) 45 (15.41%)
0.76 0.25 1.60 0.13 0.83 0 0 0.03 12.84 2.52 0.43 16.61 24.59 0 13.20
0.449 0.801 0.111 0.896 0.421 1.0 1.0 0.953
