Size at birth and blood pressure: cross sectional study in 8-11 year old children

Publication bias and heterogeneity in the relationship between systolic blood pressure, birth weight, and catch-up growth--a meta analysis

OBJECTIVE

To use meta-analytic techniques to formally examine (1) publication bias, and (2) between-study heterogeneity in the reported regression coefficient of systolic blood pressure (SBP) on birth weight, adjusting for current weight.

DATA IDENTIFICATION

A total of 55 separate analyses reporting on 382 514 male and female subjects ranging from 0 to 75 years, summarized in a recent systematic review.

RESULTS

Some 52 of 55 analyses reported a negative regression coefficient (beta) of SBP on birth weight, adjusting for current size, and in 27 of 55 (49%) the 95% confidence interval (CI) did not include zero. A pooled estimate of the regression coefficient across studies under a random-effects model was -1.38 mmHg/kg (95% CI: -1.66 to -1.10). The magnitude of the regression coefficient was negatively correlated with the age of the study population (r = -0.44, P = 0.0007). However, there was strong evidence of publication bias with smaller studies tending to report more negative betas - the Pearson correlation between beta and its standard error (SE(beta)) was -0.55 (P < 0.0001). To examine independent effects, meta analysis regressions of beta on age and SE(beta) were run. After controlling for age, there remained strong evidence of publication bias (P = 0.002), whereas after controlling for publication bias as measured by SE(beta), the relationship between beta and age was not significant (P = 0.08).

CONCLUSIONS

This analysis strongly suggests, but does not prove, that publication bias is present when systematically examining the relationship between blood pressure and birth weight. Controlling for publication bias lessens the apparent relationship between the regression coefficient and age of the study population.

Relation of birth weight to fasting insulin, insulin resistance, and body size in adolescence

OBJECTIVE

A relationship between birth weight and the insulin resistance syndrome has been reported in adults but has not been defined in adolescents.

RESEARCH DESIGN AND METHODS

Data were analyzed in 296 children (132 girls and 164 boys) mean age 15.0 +/- 1.2 years who had euglycemic insulin clamp studies (intravenous administration of 1 mU. kg(-1). min(-1) of insulin balanced by a variable infusion of 20% glucose to maintain blood glucose at 100 mg/dl). Insulin sensitivity (M(LBM)) was determined by glucose uptake per kg lean body mass (LBM), and parents reported birth weight.

RESULTS

Birth weight ranged from 1,021 to 4,848 g (mean +/- SD 3,433 +/- 551), with 4.0% <2,500 g. Fat mass and BMI had U-shaped relations with birth weight after adjustment for race, age, sex, and blood pressure. Lean mass index (lean mass/height squared) was stable across birth weight quartiles. Fasting insulin decreased nonsignificantly across birth weight quartiles but became significant after adjustment for adolescent weight (P = 0.008). Although M(LBM) was highest in the highest birth weight quartile, the pattern was not significant. Triglycerides tended to increase with birth weight, whereas LDL cholesterol (LDL-C) and HDL cholesterol (HDL-C) tended to decrease. Blood pressure was unrelated to birth weight.

CONCLUSIONS

In this cohort, fat mass was greater in adolescents with low and high birth weight; fasting insulin was lower with higher birth weight after adjustment for adolescent weight. Insulin sensitivity increased nonsignificantly with birth weight.

The role of the placenta in fetal programming-a review

The fetal origins hypothesis proposes that adult cardiovascular and metabolic disease originate through developmental plasticity and fetal adaptations arising from failure of the materno-placental supply of nutrients to match fetal requirements. The hypothesis is supported by experimental data in animals indicating that maternal nutrition can programme long term effects on the offspring without necessarily affecting size at birth. There is now evidence linking body composition in pregnant women and the balance of nutrient intake during pregnancy with raised levels of cardiovascular risk factors in the offspring. Maternal body composition and diet are thought to affect fetal development and programming as a result of both direct effects on substrate availability to the fetus and indirectly through changes in placental function and structure. Alterations in placental growth and vascular resistance, altered nutrient and hormone metabolism in the placenta, and changes in nutrient transfer and partitioning between mother, placenta and fetus all have important effects on the fetal adaptations thought to be central to programming. Future interventions to improve placental function are likely to have lifelong health benefits for the offspring.

The influence of zygosity status on blood pressure and on lipid profiles in male and female twins

OBJECTIVE

To study the influence of zygosity on blood pressure and serum lipid concentrations among male and female twins.

SETTING

Department of Endocrinology, Odense University Hospital, Denmark.

PARTICIPANTS

A total of 125 monozygotic and 178 dizygotic twin pairs aged 55-74 years of age, ascertained from The Danish Twin Register.

DESIGN

Population-based cross-sectional study.

MAIN OUTCOME MEASURES

Blood pressure and serum lipid concentrations.

RESULTS

The prevalence of hypertriglyceridemia and hypercholesterolemia were higher among monozygotic compared with dizygotic twins, whereas the prevalence of hypertension was similar. The level of triglycerides [0.28 (0.44) versus 0.18 (0.41), P = 0.01] and total cholesterol [1.82 (0.17) versus 1.78 (0.19), P = 0.03] were significantly higher in monozygotic compared with dizygotic twins. Systolic blood pressure was non-significantly higher among monozygotic twins (136.8 (21.3) versus 134.1 (19.6), P = 0.10). When comparing monozygotic and dizygotic twins within each sex group, the difference in triglyceride level was only apparent among male twins and the differences in systolic blood pressure and total cholesterol were only seen among female twins. Birth weight as determined in a subgroup of the population was similar in monozygotic and dizygotic twins.

CONCLUSIONS

Zygosity status per se influences fasting serum triglycerides and total-cholesterol and to some extent systolic blood pressure in twins, supporting an influence of an intrauterine component on lipid profiles. The influence is independent of birth weight and seems to be sex-specific.

Birth weight and blood pressure in young adults: a prospective twin study

BACKGROUND

The intrauterine environment may be a critical period for the development of hypertension in later life. In the present study, we applied the twin approach to estimate the contribution of genetic and environmental causes that may underlie the birth weight-adult blood pressure association.

METHODS AND RESULTS

Birth weights of 418 twin pairs were obtained prospectively, and resting and 24-hour ambulatory blood pressures were obtained at the age of 18 to 34 years. In women, resting systolic blood pressure decreased 4.27 mm Hg (P<0.001) and diastolic pressure decreased 2.18 mm Hg (P=0.02) per kilogram increase in birth weight. Similar associations were found for ambulatory measurements, although these were somewhat less pronounced. Pair-wise analysis confirmed these findings: twin pairs of whom both members had a low birth weight (<2500 g) had a higher systolic blood pressure compared with twins who both had a high birth weight (>/=2500 g). Systolic blood pressure of the lightest of a low-birth-weight pair was >/=4.7 mm Hg (P=0.02) higher and of the heaviest >/=2.4 mm Hg higher (P=0.2) than similar measurements in high-birth-weight pairs. Intrapair differences in blood pressure between the lightest and the heaviest at birth were only present in low-birth-weight pairs. The results were similar for monozygotic and dizygotic twin pairs. In men, no associations were found between birth weight and adult blood pressure.

CONCLUSIONS

These findings suggest that prenatal programming of adult blood pressure occurs at least in female twins. We suggest that particularly maternal influences, experienced by both twin members, may underlie the association between birth weight and blood pressure. The fetoplacental unit seems to influence blood pressure only when both fetuses had low birth weight.

Linear catch-up growth does not increase the risk of elevated blood pressure and reduces the risk of overweight in males

OBJECTIVES

To analyse if size at birth is associated with blood pressure and body mass index (BMI) at conscription in males, and if linear catch-up growth in height modifies these associations.

DESIGN

A population-based cohort study of 276 033 single-born males aged 17-24. Information from the Swedish Birth Register was individually linked to the Swedish Conscript Register. Systolic blood pressure was standardized for final height.

RESULTS

Compared to males not being small for gestational age at birth, males being light for gestational age [<-2 standard deviation scores (SDS)] were at increased risk of high systolic blood pressure [odds ratio (OR) 1.33; 95% confidence intervals (CI) 1.20-1.46], and a short adult stature was associated with a further increased risk [OR 1.65 (CI 1.13-2.40)]. Being born short for gestational age (<-2 SDS) was associated with a slightly increased risk of high systolic blood pressure [OR 1.16 (CI 1.04-1.29)], and linear catch-up growth in height did not increase this risk. Males born short for gestational age, who also were short at conscription, had an increased risk of a high BMI [OR 1.65 (CI 1.25-2.19)].

CONCLUSIONS

Males born light for gestational age have an increased risk of high systolic blood pressure, especially if they end up with short adult stature. Being born short for gestational age is associated with a slightly increased risk of high systolic blood pressure, and catch-up growth is not associated with a further risk. Lack of catch-up growth is, among males born short for gestational age, associated with an increased risk of overweight.

Do genetic factors contribute to the association between birth weight and blood pressure?

OBJECTIVES

To evaluate whether genetic factors contribute to the association between low birth weight and increased blood pressure among adolescents.

DESIGN

Historical cohort study of twin pairs. It was evaluated whether (1) a negative association between birth weight and systolic blood pressure was found in the overall twin sample and (2) whether the intrapair difference in birth weight correlated with the intrapair difference in systolic blood pressure-thereby controlling for the effect of genetic factors (all in monozygotic and on average half in dizygotic pairs).

SETTING

The Minnesota Twin Family Study.

PARTICIPANTS

1311 pairs of adolescent twins.

MAIN RESULTS

A negative association between birth weight and systolic blood pressure was retrieved in the overall sample. The regression coefficient after controlling for current weight was -1.88 mm Hg/kg (SE 0.61), which corresponds to results from previous studies of singleton adolescents. The regression coefficient fell to -0.64 mm Hg/kg (SE 0.86) when the intrapair analyses were used. The largest reduction was observed among monozygotic twins: from -2.44 mm Hg/kg (SE 0.75) in the overall monozygotic twin sample to -1.06 mm Hg/kg (SE 1.14) in the analyses of the within monozygotic pair differences.

CONCLUSION

The association between low birth weight and increased blood pressure later in life is well established. "The fetal programming hypothesis" suggests that the association is caused by intrauterine malnutrition while a new hypothesis "the fetal insulin hypothesis" proposes that genetically determined insulin resistance also contributes significantly to the association. A recent twin study of middle aged twins showed no evidence for an influence of genetic factors while this larger study provides support for the fetal insulin hypothesis: the association between birth weight and blood pressure attenuated among adolescents when genetic factors were controlled. Together this suggests an important contribution of genetic factors to the association between fetal growth and systolic blood pressure in adolescence.

The effects of birth weight and postnatal linear growth retardation on blood pressure at age 11-12 years

STUDY OBJECTIVE

To determine the effects of birth weight and linear growth retardation (stunting) in early childhood on blood pressure at age 11-12 years.

DESIGN

Prospective cohort study.

SETTING

Kingston, Jamaica.

PARTICIPANTS

112 stunted children (height for age < -2 SD of the NCHS references) and 189 non-stunted children (height for age > -1 SD), identified at age 9-24 months by a survey of poor neighbourhoods in Kingston.

MAIN RESULTS

Current weight was the strongest predictor of systolic blood pressure (beta= 4.90 mm Hg/SD weight 95%CI 3.97, 5.83). Birth weight predicted systolic blood pressure (beta = -1.28 mm Hg/SD change in birth weight, 95% CI -2.17, -0.38) after adjustment for current weight. There was a significant negative interaction between stunting in early childhood and current weight indicating a larger effect of increased current weight in children who experienced linear growth retardation in early childhood. There was no interaction between birth weight and current weight. The increase in blood pressure from age 7 to age 11-12 was greater in children with higher weight at age 11-12 and less in children with higher birth weight and weight at age 7.

CONCLUSIONS

Birth weight predicted systolic blood pressure in Jamaican children aged 11-12. Postnatal growth retardation may potentiate the relation between current weight and blood pressure. Greater weight gain between ages 7 and 11 was associated with a greater increase in systolic blood pressure. The relation between growth and later blood pressure is complex and has prenatal and postnatal components.

Placental weight and placental ratio as predictors of later blood pressure in childhood

OBJECTIVE

A significant inverse relationship between blood pressure and birth weight is firmly established. This association may be the result of fetal adaptations to an adverse intrauterine environment. Further markers of intrauterine growth include the weight of the placenta and the placental ratio (the ratio of placental weight to birth weight). A number of studies suggest that a decreased placental weight or an elevated placental ratio may be independent risk factors for subsequent high blood pressure. The overall evidence for this is, however, inconclusive. The purpose of the present study was to clearly define the relationships between placental weight, placental ratio and subsequent blood pressure during childhood.

DESIGN

Prospective cohort study of 2507 singleton children, born at term during 1989-1992. Blood pressures were recorded at ages 1, 3 and 6 years, using a semi-automated oscillometric device.

RESULTS

Inverse relationships existed between both systolic and diastolic blood pressure and placental weight, adjusted for current weight at ages 1, 3 and 6 years. The relationships between placental weight and systolic blood pressure were statistically significant at ages 1 and 3 years. There was no consistent relationship between placental weight and later blood pressure within birth weight categories. No clinically or statistically significant association was seen between the placental ratio and either systolic or diastolic blood pressures at any age.

CONCLUSIONS

Birth weight, rather than placental weight or their ratio, is the early life factor most importantly related to subsequent blood pressure in childhood.

Impact of low birth weight and cardiovascular risk factors on endothelial function in early adult life

BACKGROUND

Low birth weight is related to increased risk of coronary heart disease in adults and recently has been associated with vascular endothelial dysfunction in children. We investigated whether the relation between birth weight and endothelial function was still present in early adult life and whether there was an interaction with emerging risk factors.

METHODS AND RESULTS

In 315 adults (165 women, 150 men, aged 20 to 28 years), high-resolution ultrasound was used to determine endothelium-dependent and -independent vascular responses of the brachial artery. Vascular measures were related to classic risk factors (smoking history, lipid profile, blood pressure, fasting insulin, exercise capacity, body mass index, and combined risk score) and birth weight. Low birth weight was associated with reduced flow-mediated dilation (coefficient=0.18 kg(-1), 95% CI 0.004 to 0.35, P:=0.04) but not with endothelium-independent dilation. The difference in flow-mediated dilation between the top and bottom fifths of birth weight was the same as between smokers and nonsmokers. Increasing levels of acquired risk factors overwhelmed the association, and there was a significant interaction of risk score with the birth weight-endothelial function relation (coefficient of interaction term [birth weightxrisk score] = -0.12, 95% CI -0.22 to -0.03, P:=0.01).

CONCLUSIONS

Low birth weight is associated with endothelial dysfunction in young adults. This is most marked in individuals with lower risk factor profiles and may be relevant to the pathogenesis of atherosclerosis in later life.

Body size at birth and blood pressure among children in developing countries

BACKGROUND

Studies in developed countries have shown that reduced fetal growth is related to raised blood pressure in childhood and adult life. Little is known about this association in developing countries, where fetal growth retardation is common.

METHODS

In 1994-1995, we measured blood pressure in 1570 3-6-year-old children living in China, Guatemala, Chile, Nigeria and Sweden. We related their blood pressure to patterns of fetal growth, as measured by body proportions at birth. The children were all born after 37 weeks gestation and weighed more than 2.5 kg at birth.

RESULTS

In each country, blood pressure was positively related to the child's current weight. After adjusting for this and gender, systolic pressure was inversely related to size at birth in all countries except Nigeria. In Chile, China and Guatemala, children who were proportionately small at birth had raised systolic pressure. For example, in Chile, systolic pressure adjusted for current weight increased by 4.9 mmHg (95% CI : 2.1, 7.7) for every kilogram decrease in birthweight, by 1 mmHg (95% CI : 0.4, 1.6) for every centimetre decrease in birth length, and by 1.3 mmHg (95% CI : 0.4, 2.2) for every centimetre decrease in head circumference at birth. In Sweden, systolic pressure was higher in children who were disproportionately small, that is thin, at birth. Systolic pressure increased by 0.3 mmHg (95% CI : 0.0, 0.6) for every unit (kg/m3) decrease in ponderal index at birth. These associations were independent of the duration of gestation.

CONCLUSIONS

Raised blood pressure among children in three samples from China, Central and South America is related to proportionate reduction in body size at birth, which results from reduced growth throughout gestation. The relation between fetal growth and blood pressure may be different in African populations. Proportionately reduced fetal growth is the prevalent pattern of fetal growth retardation in developing countries, and is associated with chronic undernutrition among women. Improvement in the nutrition and health of girls and young women may be important in preventing cardiovascular disease in developing countries.

Dermatoglyphic patterns, very low birth weight, and blood pressure in adolescence

AIMS

To test the null hypotheses that finger and palm prints have no relation with fetal growth or adolescent blood pressure.

METHODS

All 128 singleton, unimpaired, very low birth weight (VLBW; < or =1500 g) infants born to mothers resident in the county of Merseyside in 1980 and 1981 were studied retrospectively. The comparison group consisted of 128 age, sex, and school matched children. Main outcome measures were blood pressure at age 15 years, birth weight ratio, fingerprint patterns, and palmar AtD angles.

RESULTS

The VLBW index population had a significantly higher systolic blood pressure than the comparison group (mean difference 3.2 mm Hg). The difference in diastolic blood pressure between the VLBW index and the matched comparison group was not significant. No significant differences were found in the palmar AtD angles or in the fingerprint proportions of arches, loops, and whorls and no correlation was found between fingerprint patterns and blood pressure. Among the VLBW index population, both height and right palmar AtD angle were independently and significantly correlated with and explained 12.1% of the variance in the systolic blood pressure. Birth weight ratio, as a measure of fetal growth restriction, had no significant correlation with systolic blood pressure.

CONCLUSIONS

The higher systolic blood pressure of adolescents who were of very low birth weight compared with the matched comparison group is not associated with fingerprint patterns or birth weight ratio as markers for fetal growth restriction.

Evidence for genetic factors explaining the birth weight-blood pressure relation. Analysis in twins

Epidemiological studies have consistently shown an inverse association between birth weight and systolic blood pressure in later life after adjustment for current size. To examine whether this association is explained by intrauterine or genetic factors, we investigated birth weight and blood pressure data in 53 dizygotic and 61 monozygotic adolescent twin pairs. Birth weight was obtained from the mothers. Blood pressure measurements were performed 6 times at rest and during mental stress. The dizygotic but not the monozygotic twins with the lowest birth weight from each pair had a systolic blood pressure measured at rest and during the reaction time experiment that was higher compared with their cotwins with the highest birth weight (dizygotic twins: blood pressure at rest, 119. 4+/-9.7 mm Hg versus 117.3+/-8.5 mm Hg, P=0.07, and during a reaction time task, 126.2+/-10.8 versus 123.6+/-9.5, P=0.09; monozygotic twins: blood pressure at rest, 117.4+/-6.4 versus 118. 4+/-9.0, P=0.4, and during a reaction time task, 122.9+/-8.4 versus 124.2+/-10.8, P=0.2). The differences in blood pressure between the cotwins with the lowest and the cotwins with the highest birth weight were different in dizygotic compared with monozygotic twin pairs (for blood pressure at rest, P=0.05; for blood pressure during reaction time, P=0.03). After adjustment for differences in current weight, intrapair differences in birth weight were negatively and significantly associated with differences in systolic blood pressure at rest and during the reaction time task in dizygotic twins (regression coefficient, -5.7 mm Hg/kg [95% confidence interval, -10.4 to -1.0] and -6.3 [-12.7 to 0], respectively) but not in monozygotic twins (-0.1 [-5.4 to 5.2] and +3.5 [-1.8 to 8.8], respectively). Interaction analysis indicated that the associations were different between dizygotic twins and monozygotic twins (P=0.1 and P<0.05, respectively). These data suggest that genetic factors may play an important role in the association between birth weight and blood pressure.

Fetal and childhood growth and hypertension in adult life

The association between low birth weight and raised blood pressure has been extensively replicated. Little is known about the way childhood growth modifies the effects of low birth weight. We report on the fetal and childhood growth of 1958 men and women who received treatment for hypertension and belong to a cohort of 7086 people born in Helsinki, Finland, during 1924-1933. As expected, the men and women who developed hypertension had low birth weight (P=0.002). They were also shorter in body length at birth (P=0.02). After birth they experienced accelerated growth, so that by 7 years their heights and weights were approximately average. In a simultaneous regression, both birth length and tall height had statistically significant although opposing effects on hypertension (P=0.003 for birth length and 0.009 for height at 7 years). Accelerated postnatal growth was associated with better childhood living conditions. Children who later developed both hypertension and type 2 diabetes, rather than hypertension alone, had small placental size as well as small body size at birth, and their accelerated postnatal growth continued beyond 7 years. We suggest that hypertension may originate through retarded growth in utero followed by accelerated postnatal growth as a result of good living conditions. Retarded fetal growth leads to permanently reduced cell numbers in the kidney and other tissues, and subsequent accelerated growth may lead to excessive metabolic demand on this limited cell mass.

The role of size at birth and postnatal catch-up growth in determining systolic blood pressure: a systematic review of the literature

OBJECTIVE

To conduct a systematic review in order to (i) summarize the relationship between birthweight and blood pressure, following numerous publications in the last 3 years, (ii) assess whether other measures of size at birth are related to blood pressure, and (iii) study the role of postnatal catch-up growth in predicting blood pressure.

DATA IDENTIFICATION

All papers published between March 1996 and March 2000 that examined the relationship between birth weight and systolic blood pressure were identified and combined with the papers examined in a previous review.

SUBJECTS

More than 444,000 male and female subjects aged 0-84 years of all ages and races.

RESULTS

Eighty studies described the relationship of blood pressure with birth weight The majority of the studies in children, adolescents and adults reported that blood pressure fell with increasing birth weight, the size of the effect being approximately 2 mmHg/kg. Head circumference was the only other birth measurement to be most consistently associated with blood pressure, the magnitude of the association being a decrease in blood pressure by approximately 0.5 mmHg/cm. Skeletal and non-skeletal postnatal catch-up growth were positively associated with blood pressure, with the highest blood pressures occurring in individuals of low birth weight but high rates of growth subsequently.

CONCLUSIONS

Both birth weight and head circumference at birth are inversely related to systolic blood pressure. The relationship is present in adolescence but attenuated compared to both the pre- and post-adolescence periods. Accelerated postnatal growth is also associated with raised blood pressure.

Fetal, infant, and childhood growth are predictors of coronary heart disease, diabetes, and hypertension in adult men and women

Many human fetuses have to adapt to a limited supply of nutrients. In doing so they permanently change their structure and metabolism. These programmed changes may be the origins of a number of diseases in later life, including coronary heart disease, hypertension, and noninsulin- dependent diabetes. We review epidemiologic studies in which the incidence of these diseases has been related to the recorded, early growth of individuals, while considering factors in the adult lifestyle, such as obesity and socioeconomic status. We discuss possible mechanisms. For hypertension these mechanisms include placentation, maternal blood pressure, fetal undernutrition; childhood growth, activation of the renin-angiotensin system, renal structure, programming of the hypothalamic-pituitary-adrenal axis, vascular structure, and sympathetic nervous activity. For noninsulin-dependent diabetes we discuss mechanisms concerning both insulin resistance and insulin deficiency. We include a review of evidence for the programming of serum cholesterol and clotting factor concentrations. We address the timing of critical windows for coronary heart disease, reviewing studies that allow assessment of the relative importance of fetal, infant, and childhood growth. We argue for a research strategy that combines clinical, animal, and epidemiological studies.

C-reactive protein concentration in children: relationship to adiposity and other cardiovascular risk factors

Whether or not C-reactive protein (CRP) predicts heart disease in adults because it is a marker of damage or atherosclerosis is difficult to assess. In children, there is no confounding with coronary disease or active smoking. We measured CRP in 699 children aged 10-11 years. CRP levels were 47% higher in girls than boys, and rose with age by 15%/year. CRP levels were 270% (95% CI, 155-439%) higher in the top fifth than the bottom fifth of Ponderal index (weight/height(3)). After adjustment, CRP levels remained 104% (95% CI, 23-236%) higher in the 56 children of South Asian origin. CRP was unrelated to: birth weight, height, social class, Helicobacter pylori infection or passive smoke exposure. CRP was correlated with several cardiovascular risk factors, but only fibrinogen (r = 0.33, P = 0.0001), HDL-cholesterol (r = -0.13, P = 0.0006), heart rate (r = 0.12, P = 0.002) and systolic blood pressure (r = 0.08, P = 0.02) remained statistically significant after adjustment. We conclude that adiposity is the major determinant of CRP levels in children while physical fitness has a small independent effect. The strong relationships with fibrinogen and HDL-cholesterol suggest a role for inflammation throughout life in the development of atherosclerosis and cardiovascular disease. Longitudinal studies are needed to determine whether these associations reflect long term elevations of these risk factors in some individuals, or short term fluctuations in different individuals.

Parental recall of birth weight: how accurate is it?

OBJECTIVE

To assess the accuracy of parental recall of birth weight in a British population and to investigate whether social class and age of the child significantly influence the accuracy of recalled birth weight.

METHODS

A questionnaire was given to parents whose children were participating in a blood pressure study and the hospital records were retrieved to check the birth weight data.

RESULTS

At the time of the study, the children (n = 649) ranged in age from 6 to 15 years. Seventy five per cent of the recalled birth weights were within 50 g of that recorded in the hospital records. No significant associations were found between the difference in birth weights (recalled birth weight minus hospital record) and social class of the parents or age of the child at time of data collection.

CONCLUSION

This large study shows that parental recall of birth weight is good across the social classes and up to 16 years after delivery. There was no evidence of systematic bias, which would prejudice results of studies on the relation of birth weight to adult hypertension.

In utero programming of cardiovascular disease

Low birth weight, thinness and short body length at birth are now known to be associated with increased rates of cardiovascular disease and non-insulin dependent diabetes in adult life. The fetal origins hypothesis proposes that these diseases originate through adaptations which the fetus makes when it is undernourished. These adaptations may be cardiovascular, metabolic or endocrine. They permanently change the structure and function of the body. Prevention of the diseases may depend on prevention of imbalances in fetal growth or imbalances between pre- and post-natal growth, or imbalances in nutrient supply to the fetus.

Within pair association between birth weight and blood pressure at age 8 in twins from a cohort study

OBJECTIVES

To study the association between birth weight and blood pressure in children from multiple pregnancies (multiplets), mostly twins, to determine whether maternal or genetic factors are responsible for the association.

DESIGN

Cohort study.

SETTING

Southern Tasmania.

SUBJECTS

888 children including 104 multiplets (32 monozygotic, 72 dizygotic).

MAIN OUTCOME MEASURE

Systolic blood pressure (mm Hg).

RESULTS

Blood pressure decreased with birth weight and increased with current body mass. After adjustment for age and body mass, systolic blood pressure changed by -1.94 mm Hg (95% confidence interval -2.89 to -0.98) per 1 kg increase in birth weight of singletons. For multiplets, blood pressure changed by -7.0 mm Hg (-10.1 to -3.9) for each 1 kg increase in birth weight. This was little altered in within pair analyses (-5.3, -13.8 to 3.2) and was similar for both monozygotic (-6.5, -22.5 to 9.4) and dizygotic (-4.9, -15.8 to 6.0) pairs.

CONCLUSION

Because the association between birth weight and blood pressure was largely unchanged in within pair analyses, exposures originating in the mother (such as nutritional status) cannot be wholly responsible. The association also remained within monozygotic pairs, suggesting that genetic predisposition is not wholly responsible either. The principal causal pathway must concern mechanisms within the fetoplacental unit. The stronger association in multiplets suggests that factors adversely influencing both blood pressure and birth weight are more prevalent in multiple pregnancies.

Blood pressure and birthweight in first year university students aged 18-25

There have been many papers examining the relationship between blood pressure and birthweight but although the association is clearly established in adults and children findings in adolescence and young adults have been inconsistent. The objective of this study was to examine the relationship between blood pressure and birthweight in young adults. The blood pressure of 1358 university students aged 18-25 was recorded at a screening medical examination and their birthweight from parental report. Using linear regression analysis, systolic blood pressure, after adjustment for age, weight and height, decreased by 2.00 mmHg (-3.8, -0.2) for every kg increase in birthweight in females. The relationship was negative but non-significant in males. Substituting body mass index (BMI) for weight in the regression analysis produced similar results. There was a smaller and non-significant relationship between diastolic blood pressure and birthweight which is consistent with other studies. This study confirms the inverse relationship between systolic blood pressure and birthweight in young adults and provides some support for the hypothesis that undernutrition in utero contributes to the development of cardiovascular disease in adults.

The relationship between birth weight and blood pressure amplifies from childhood to adulthood

OBJECTIVE

To investigate relationships between birth characteristics and blood pressure at age 20 years and to assess whether effects of birth weight on blood pressure are amplified from childhood to adulthood.

DESIGN

A longitudinal study of 584 men and women from Adelaide, Australia, examined previously at 8 years and followed up at age 20 years.

RESULTS

Birth weight was negatively associated with systolic pressure at age 20 years in men (regression coefficient 2.6 mmHg per kg; 95% confidence interval 0.7, 4.4) and women (regression coefficient 4.6 mmHg per kg; 95% confidence interval 2.9, 6.4), after adjustment for current weight There was an interaction with current size (P = 0.05 for men and P = 0.09 for women), such that effects were enhanced among individuals with relatively high weight or weight for height. Shortness at birth, thinness at birth, and low birth weight relative to placental weight were also associated with elevated systolic pressure at age 20 years. Effects of birth weight on blood pressure were stronger at age 20 than at age 8 years (P < 0.01 for men and P = 0.03 for women). This was not due simply to increased variability of blood pressure in adulthood. There were greater rises in blood pressure with age among individuals of relatively low birth weight.

CONCLUSIONS

These findings are further evidence that poor fetal growth is associated with elevated blood pressure in later life. The results support the hypothesis that the relationship is amplified with increasing age.

Twins and maternal smoking: ordeals for the fetal origins hypothesis? A cohort study

OBJECTIVE

To assess the direct and indirect effects of being a twin, maternal smoking, birth weight, and mother's height on blood pressure at ages 9 and 18 years.

DESIGN

Longitudinal study.

SUBJECTS

Cohort born in 1972-3.

SETTING

Dunedin, New Zealand.

MAIN OUTCOME MEASURE

Blood pressure at ages 9 and 18 years.

RESULTS

Compared with singletons, twins had a systolic blood pressure 4.55 (95% confidence interval 1.57 to 7.52) mm Hg lower at age 9 after adjustment for direct and indirect effects of sex, maternal smoking, mother's height, socioeconomic status, and birth weight, as well as concurrent height and body mass index. Blood pressure in children whose mothers had smoked during pregnancy was 1.54 (0.46 to 2.62) mm Hg higher than in those whose mothers did not. The total effect of birth weight on systolic blood pressure at age 9 was -0.78 (-1.76 to 0.20) mm Hg and that for mother's height was 0.10 (0.06 to 0.14) mm Hg. Similar results were obtained for systolic blood pressure at age 18. The total effect of twins, maternal smoking, and birth weight on diastolic blood pressure was not significant at either age.

CONCLUSIONS

Twins had lower birth weight and lower systolic blood pressure at ages 9 and 18 than singletons. This finding challenges the fetal origins hypothesis. The effect of maternal smoking was consistent with the fetal origin hypothesis in that the infants of smokers were smaller and had higher blood pressure at both ages. This may be explained by pharmacological rather than nutritional effects. The total effect of birth weight on systolic blood pressure, after its indirect effect working through concurrent measures of height and body mass index was taken into account, was small.

Evidence for an association between birth weight and blood pressure

Evidence is presented to support the concept that there is an association between birth weight and blood pressure in humans. This relationship probably reflects an interaction between the genetic make-up of the individual and the environment. On average, a decrease in birth weight is associated with a rise in blood pressure in adult life.

Association of blood pressure in adolescence with birthweight

AIMS

To compare the blood pressure of very low birthweight infants with that of normal birthweight controls in adolescence.

METHODS

A cohort of all infants of birthweight < or = 1500 g born to women resident in the county of Merseyside in 1980-1 was followed up at age 15 years with age, sex, and school matched controls. Growth indices and blood pressures were measured under standard conditions. The smoking history of mothers and children and their status for several socioeconomic variables were documented. In a matched pairs analysis systolic and diastolic blood pressures were compared for cases and controls before and after adjusting for height, weight, and body mass index.

RESULTS

There were 172 singleton 15 year old survivors of birthweight < 1500 g out of 40,321 live births of Merseyside residents in 1980-1. Of the 172 survivors, 128 (74%) who had no clinical disability and 11 (6%) with a clinical disability but attending normal schools, were assessed with individually matched age, sex, and school controls. Twenty three (13%) had a clinical disability and were attending special schools; these were assessed without controls. Ten (6%) children refused or were unavailable for assessment. The systolic blood pressure was significantly higher in cases than in controls; the mean of the difference was 3.2 mm Hg. The diastolic blood pressure was also higher in the cases, but the difference was not significant. The controls were significantly heavier (4.4 kg), taller (4.0 cm), with larger head circumference (1.5 cm) than the cases. The difference in body mass index was not significant. Adjusting for height, weight, or body mass index increased the difference in systolic blood pressure between cases and controls. There were no significant differences in the socioeconomic variables, but what differences did exist favoured the controls. There was also a higher prevalence of smoking among the children and the mothers of the cases than the controls.

CONCLUSIONS

The study supports the hypothesis that in adolescents variation in systolic blood pressure has its origins in fetal development. Some of the variation could be attributed to socioeconomic differences.

Flow-mediated dilation in 9- to 11-year-old children: the influence of intrauterine and childhood factors

BACKGROUND

Early life factors, particularly size at birth, may influence later risk of cardiovascular disease, but a mechanism for this influence has not been established. We have examined the relation between birth weight and endothelial function (a key event in atherosclerosis) in a population-based study of children, taking into account classic cardiovascular risk factors in childhood.

METHODS AND RESULTS

We studied 333 British children aged 9 to 11 years in whom information on birth weight, maternal factors, and risk factors (including blood pressure, lipid fractions, preload and postload glucose levels, smoking exposure, and socioeconomic status) was available. A noninvasive ultrasound technique was used to assess the ability of the brachial artery to dilate in response to increased blood flow (induced by forearm cuff occlusion and release), an endothelium-dependent response. Birth weight showed a significant, graded, positive association with flow-mediated dilation (0.027 mm/kg; 95% CI, 0.003 to 0.051 mm/kg; P=.02). Childhood cardiovascular risk factors (blood pressure, total and LDL cholesterol, and salivary cotinine level) showed no relation with flow-mediated dilation, but HDL cholesterol level was inversely related (-0.067 mm/mmol; 95% CI, -0.021 to -0.113 mm/mmol; P=.005). The relation between birth weight and flow-mediated dilation was not affected by adjustment for childhood body build, parity, cardiovascular risk factors, social class, or ethnicity.

CONCLUSIONS

Low birth weight is associated with impaired endothelial function in childhood, a key early event in atherogenesis. Growth in utero may be associated with long-term changes in vascular function that are manifest by the first decade of life and that may influence the long-term risk of cardiovascular disease.