Cohort Study On The Effects Of High Birth Weight And Overweight&Obesity On Blood Pressure Among Children And Adolescents

[Background]Since the hypothesis of "fetal origin of adult disease" was proposed by British scholar Barker in the1980s, the long-term effects on health of intrauterine fetal growth have attached more and more attention. Birth weight is an important indicator reflecting intrauterine growth and nutritional status, but also one of the factors influencing postnatal developmental levels and health status. Many of the previous studies concerned the growth, development and health status of children with low birth weight, and low birth weight has been affirmed to be a risk factor for many diseases.In the last three decades, the birth weight and incidences of fetal macrosomia, blood pressure levels of children and adolescents and prevalence of hypertension have been all on the increasing track in both developed and some developing countries. The effects of high birth weight on blood pressure of children and adolescents are worthy concerning. Meanwhile, studies of influencing factors on blood pressure of children and adolescents have significant implications for targeted prevention of hypertension in children and adolescents.[Objective]The objective of this study was to explore the effects of high birth weight, overweight&obesity in childhood and adolescence on blood pressure of children and adolescents, and to analyze the influencing factors of blood pressure in childhood and adolescence.[Methods]This study was a cohort study with high birth weight as the exposure factor. One city county-level (Jiangyin) and two districts (Huishan District and Xishan District) in Wuxi of Jiangsu Province were chosen as the study fields. The subjects were single born during1993to1995, among whom, subjects whose birth weight≥4000g were divided into exposed group, and <4000g and≥2500g were divided into unexposed group. When the birth cohort was established, subjects in unexposed group were matched by sex and "birth date±2months". And subjects whose parents or grandparents had hypertension or diabetes were excluded. Two follow-up investigations were finished during Oct.2005to Sep.2006and June2011to May2012, respectively.When the cohort was first established, the database included maternal information during pregnancy and perinatal status. During the two follow-up investigations, demographic characteristics and personal habits were inquired in the questionnaires and height, weight and blood pressure were measured. Epidata3.1software was used for data entry, and SAS9.2and LISREL8.7for data analysis. The blood pressure was taken as outcome variables (systolic BP, diastolic BP and proportion of elevated BP). Variance analysis, χ2test, random intercept growth model, generalized linear mixed model, linear regression, logistic regression, and structural equation model were used to analyze the effects of high birth weight, overweight&obesity on blood pressure and the influencing factors of blood pressure in children and adolescence.[Results]1. Overview of the cohortA total of1595pairs (3190) eligible subjects were included in the established cohort. And2256subjects finished questionnaires and measurements in two follow-up investigations, including1126subjects from exposed group and1130from unexposed group, among whom boys accounted for66.45%(1499) and girls for33.55%(757) with sex balance between exposed and unexposed groups. Exposure status, birth year and sex had no statistically significant different between subjects who were followed-up and who lost to follow up.2. Comparing the general information in exposed group with unexposed groupThere were no statistically differences of maternal demographic characteristics and pregnancy situation between subjects in the exposed group and unexposed group. However, the maternal height, weight and weight gain during pregnancy were significantly higher of the exposed group than those of the unexposed group. Besides, exposed group had significantly higher proportion of prolonged pregnancy (gestational age≥42weeks), and higher birth length and head circumference than those of unexposed group.During the follow-up investigation in childhood, the proportion of the average daily TV time≥1hour in exposed group was36.93%, lower than42.06%in unexposed group. In the follow-up investigation of adolescents, the prevalence of monophagia in exposed group was lower than that of unexposed group, but the proportion of average daily exercise time≥2hours was higher than that of unexposed group.3. The effects of high birth weight on blood pressure In childhoos, the SBP and DBP in exposed group were100.40±10.58mmHg,65.45±8.95mmHg, respectively, while in unexposed group, it was99.81±9.96mmHg,65.02±8.65mmHg, respectively. The average of SBP of adolescents with higher birth weight was110.90±9.49mmHg, which was significantly higher than that of adolescents with normal birth weight (109.36±9.20mmHg)(P<0.0001). The average of DBP of adolescents was72.16±6.34mmHg in exposed group,71.63±6.39mmHg in unexposed group. In HBW group, the rates of hypertension were6.93%in childhood and3.55%in adolescence, in comparison with6.46%in childhood and2.83%in adolescence in normal birth weight group. The "proportions of elevated BP"(hypertension and prehypertension) were14.30%and20.78%in childhood and adolescence with high birth weight respectively, which were significantly higher than those of normal birth weight group (11.50%,16.64%), with RR of1.24(95%CI:1.00-1.54) and1.25(95%CI:1.05-1.49), respectively. After adjustment of repeated measurements and some other factors, the SBP and proportion of elevated BP in high birth weight group were significantly higher, the parameter estimation values were0.81±0.30,0.21±0.09, respectively.Birth weight and lifestyle of often eating sweets in adolescence had significant interactions on SBP, DBP and proportion of elevated BP of adolescents. The relative excess risk of interactions (RERI) was2.71(95%CI:0.75-4.67) and attributable proportion (AP) was66.5%(95%CI:41.2-91.8) on proportion of elevated BP.4. The effects of high birth weight on overweight and obesityBMI of subjects with high birth weight was significantly higher than those with normal birth weight in both childhood and adolescence. The prevalence of overweight&obesity of subjects with high birth weight was15.99%in childhood and11.99%in adolescence, which was significantly higher than those of subjects with normal birth weight (11.59%in childhood and8.85%in adolescence), with RR of1.38(95%CI:1.12-1.70) and1.35(95%CI:1.06-1.73), respectively. After adjustment of repeated measurements, high birth weight had significant effects on BMI and proportions of overweight&obesity of children and adolescents.5. The effects of overweight and obesity on blood pressureAfter adjustment of birth weight group, maternal age, maternal occupation, pregnancy-induced hypertension, gestational age, parity, sex, age and lifestyle of often taking sweets or fried food in childhood, it was indicated that the SBP (β±E: 2.49±0.61), DBP (β±E:3.20±0.51) and proportion of elevated BP (OR=2.16,95%CI:1.52-3.08) of children who were overweight or obese had significant increased.Multivariate analysis showed that overweight or obese adolescents had significantly higher SBP (β±E:5.62±0.61) and DBP (α±E:3.35±0.42). Overweight&obesity in adolescence and high birth weight had significant interactions on proportion of elevated BP of adolescents, within which RERI was2.22(95%CI:0.42-4.02) and AP was49.5%(95%CI:22.1-76.8). The risk of elevated BP due to overweight&obesity in adolescence was2.21(95%CI:1.35-3.62) in normal birth weight group, and3.97(95%CI:2.65-5.94) in high birth weight group.6. Effect analysis of impact of birth weight and BMI on blood pressureThe total effects of birth weight on SBP and DBP in childhood were both0.04. The direct effect of birth situation (birth weight and length) on blood pressure in childhood was0.11, and the indirect effect was0.04. The effect of BMI in childhood on blood pressure was0.25.The total effect of birth weight on SBP in adolescence was0.07, comparing with0.06on DBP in adolescence. Birth situation (birth weight and length) had mainly indirect effect through BMI on BP in adolescence (0.11). The effect of BMI in adolescence on blood pressure was0.51.7. The influencing factors of blood pressure in childhoodIt was indicated in multivariate analysis that pregnancy-induced hypertension and the lifestyle of often eating fried food were the risk factors of blood pressure in childhood. With the increase of age and BMI of children, the risks of higher SBP, DBP and proportion of elevated BP increased. The SBP of boys in childhood was higher than that of girls. SBP increased with the increasing of birth length.Average daily exercise time≥2hours could reduce SBP, DBP and proportion of elevated BP. Aerobic exercise could reduce SBP and the risk of high blood pressure in childhood. Monophagia could reduce DBP and the risk of elevated BP in childhood. Children whose mothers were workers or others (teachers, cadres, business services, etc) at delivery had lower SBP than those whose mothers were farmers at delivery.8. The influencing factors of blood pressure in adolescenceThe pregnancy-induced hypertension was a risk factor of BP in adolescence. The SBP, DBP and proportion of elevated BP of male adolescents were higher than those of female. The risks of higher SBP, DBP and proportion of elevated BP increased, along with the increase of BMI of adolescents. SBP of adolescents also increased with the increasing of birth length and SBP in childhood. With the increase of age, the risks of higher DBP and proportion of elevated BP increased. Often eating sweets was the risk factor of SBP and proportion of elevated BP. Risk factors of later pregnancy period, such as complication of pregnancy, could lead to higher proportion of elevated BP in adolescence. Subjects whose father or mother had hypertension at the second follow-up had higher proportion of elevated BP.Aerobic or anaerobic exercise could reduce SBP of adolescents. Both aerobic and anaerobic exercise had effects on DBP and proportion of elevated BP.(Conclusions]1. High birth weight was the risk factor of raised BP among children and adolescents. Moreover, the interaction between HBW and dietary habit (sweet food frequently) on adolescent blood pressure was found in this study.2. High birth weight could lead to overweight and obesity in childhood and in adolescence, which were the risk factors of blood pressure. Moreover, high birth weight and overweight&obesity in adolescence had interactive effects on the proportion of elevated blood pressure.3. Birth weight had not only direct effects on BP of children and adolescence, but also indirect effects through higher BMI. But the effects of BMI on BP were higher than those of birth weight in childhood and in adolescence.4. There were gender and age differences about BP in childhood and in adolescence. The pregnancy-induced hypertension, often eating fried food in childhood and often eating sweets in adolescence had harmful effects on BP. The higher blood pressure of adolescents was related to father’s or mother’s hypertension. Aerobic exercise was the protective factor of blood pressure among children and adolescents.