Jane West

Cohort Profile: The Born in Bradford multi-ethnic family cohort study

Bradford Institute for Health Research, Bradford Teaching Hospitals Foundation Trust, Bradford, UK, School of Health Studies, University of Bradford, Bradford, UK, Edinburgh Ethnicity and Health Research Group, Centre for Population Health Sciences, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh, UK, School of Sport, Exercise and Health Sciences, Loughborough University, Leicestershire, UK, Medical Research Council Centre for Causal Analyses in Translational Epidemiology, School of Social and Community Medicine, University of Bristol, Bristol, UK, Paediatric Epidemiology Group, Centre for Epidemiology and Biostatistics, Leeds Institute of Genetics, Health and Therapeutics, Faculty of Medicine and Health, University of Leeds, Leeds, UK and Department of Health Sciences, University of York, York, UK

UK-born Pakistani-origin infants are relatively more adipose than White British infants: findings from 8704 mother-offspring pairs in the Born-in-Bradford prospective birth cohort

Background Previous studies have shown markedly lower birth weight among infants of South Asian origin compared with those of White European origin. Whether such differences mask greater adiposity in South Asian infants and whether they persist across generations in contemporary UK populations is unclear. Our aim was to compare birth weight, skinfold thickness and cord leptin between Pakistani and White British infants and to investigate the explanatory factors, including parental and grandparental birthplace. Methods We examined the differences in birth weight and skinfold thickness between 4649 Pakistani and 4055 White British infants born at term in the same UK maternity unit and compared cord leptin in a subgroup of 775 Pakistani and 612 White British infants. Results Pakistani infants were lighter (adjusted mean difference −234 g 95% CI −258 to −210) and were smaller in both subscapular and triceps skinfold measurements. The differences for subscapular and triceps skinfold thickness (mean z-score difference −0.27 95% CI −0.34 to −0.20 and −0.23 95% CI −0.30 to −0.16, respectively) were smaller than the difference in birth weight (mean z-score difference −0.52 95% CI −0.58 to −0.47) and attenuated to the null with adjustment for birth weight (0.03 95% CI −0.03 to 0.09 and −0.01 95% CI −0.08 to 0.05, respectively). Cord leptin concentration (indicator of fat mass) was similar in Pakistani and White British infants without adjustment for birth weight, but with adjustment became 30% higher (95% CI 17% to 44%) among Pakistani infants compared with White British infants. The magnitudes of difference did not differ by generation. Conclusions Despite being markedly lighter, Pakistani infants had similar skinfold thicknesses and greater total fat mass, as indicated by cord leptin, for a given birth weight than White British infants. Any efforts to reduce ethnic inequalities in birth weight need to consider differences in adiposity and the possibility that increasing birth weight in South Asian infants might inadvertently worsen health by increasing relative adiposity.

Describing differences in weight and length growth trajectories between white and Pakistani infants in the UK: analysis of the Born in Bradford birth cohort study using multilevel linear spline models

Objective To describe the growth pattern from birth to 2 years of UK-born white British and Pakistani infants. Design Birth cohort. Setting Bradford, UK. Participants 314 white British boys, 383 Pakistani boys, 328 white British girls and 409 Pakistani girls. Main outcome measures Weight and length trajectories based on repeat measurements from birth to 2 years. Results Linear spline multilevel models for weight and length with knot points at 4 and 9 months fitted the data well. At birth Pakistani boys were 210 g lighter (95% CI −290 to −120) and 0.5 cm shorter (−1.04 to 0.02) and Pakistani girls were 180 g lighter (−260 to −100) and 0.5 cm shorter (−0.91 to −0.03) than white British boys and girls, respectively. Pakistani infants gained length faster than white British infants between 0 and 4 months (+0.3 cm/month (0.1 to 0.5) for boys and +0.4 cm/month (0.2 to 0.6) for girls) and gained more weight per month between 9 and 24 months (+10 g/month (0 to 30) for boys and +30 g/month (20 to 40) for girls). Adjustment for maternal height attenuated ethnic differences in weight and length at birth, but not in postnatal growth. Adjustment for other confounders did not explain differences in any outcomes. Conclusions Pakistani infants were lighter and had shorter predicted mean length at birth than white British infants, but gained weight and length quicker in infancy. By age 2 years both ethnic groups had similar weight, but Pakistani infants were on average taller than white British infants.

Reliability of routine clinical measurements of neonatal circumferences and research measurements of neonatal skinfold thicknesses: findings from the Born in Bradford study

Summary West J, Manchester B, Wright J, Lawlor DA, Waiblinger D. Reliability of routine clinical measurements of neonatal circumferences and research measurements of neonatal skinfold thicknesses: findings from the Born in Bradford study. Paediatric and Perinatal Epidemiology 2011. Assessing neonatal size reliably is important for research and clinical practice. The aim of this study was to examine the reliability of routine clinical measurements of neonatal circumferences and of skinfold thicknesses assessed for research purposes. All measurements were undertaken on the same population of neonates born in a large maternity unit in Bradford, UK. Technical error of measurement (TEM), relative TEM and the coefficient of reliability are reported. Intra-observer TEMs for routine circumference measurements were all below 0.4 cm and were generally within ±2-times the mean. Inter-observer TEM ranged from 0.20 to 0.36 cm for head circumference, 0.19 to 0.39 cm for mid upper arm circumference and from 0.39 to 0.77 cm for abdominal circumference. Intra and inter-observer TEM for triceps skinfold thickness ranged from 0.22 to 0.35 mm and 0.15 to 0.54 mm, respectively. Subscapular skinfold thickness TEM values were 0.14 to 0.25 mm for intra-observer measurements and 0.17 to 0.63 mm for inter-observer measurements. Relative TEM values for routine circumferences were all below 4.00% but varied between 2.88% and 14.23% for research skinfold measurements. Reliability was mostly between 80% and 99% for routine circumference measurements and ≥70% for most research skinfold measurements. Routine clinical measurements of neonatal circumferences are reliably assessed in Bradford. Assessing skinfolds in neonates has variable reliability, but on the whole is good. The greater intra-observer, compared with inter-observer, reliability for both sets of measurements highlights the importance of having a minimal number of assessors whenever possible.

Physical Activity, Sedentary Time, and Fatness in a Biethnic Sample of Young Children.

Purpose This study aimed to investigate associations of objectively measured physical activity (PA) and sedentary time with adiposity in a predominantly biethnic (South Asian and White British) sample of young children. Methods The sample included 333 children age 11 months to 5 yr who provided 526 cross-sectional observations for PA and body composition. Total PA volume (vector magnitude counts per minute), daily time at multiple intensity levels (the cumulative time in activity >500, >1000, >1500, …, >6000 counts per minute), and time spent sedentary (<820 counts per minute), in light PA (820–3907 counts per minute) and in moderate-to-vigorous PA (≥3908 counts per minute) were estimated with triaxial accelerometry. Indicators of adiposity included body mass index, waist circumference, and the sum of subscapular and triceps skinfold thicknesses. Statistical analyses were performed using multilevel regression and isotemporal substitution models adjusted for confounders. Effect modification by ethnicity was examined. Results There was no evidence for effect modification by ethnicity (P interaction ≥ 0.13). In the whole sample, the accumulated time spent above 3500 counts per minute (i.e., high light-intensity PA) was inversely associated with the sum of skinfolds (&bgr; = −0.60 mm, 95% confidence interval [CI] = −1.19 to −0.021, per 20 min·d−1), and the magnitude of association increased dose dependently with PA intensity (peaking for time spent >6000 counts per minute = −1.57 mm, 95% CI = −3.01 to −0.12, per 20 min·d−1). The substitution of 20 min·d−1 of sedentary time with moderate-to-vigorous PA was associated with a lower sum of skinfolds (−0.77 mm, 95% CI = −1.46 to −0.084). Conclusions High light-intensity PA appears to be beneficial for body composition in young South Asian and White British children, but higher-intensity PA is more advantageous.

Do ethnic differences in cord blood leptin levels differ by birthweight category? Findings from the Born in Bradford cohort study

Background There is evidence that South Asian individuals have higher fat mass for a given weight than Europeans. One study reported that the greater fatness for a given birthweight may increase with increasing birthweight, suggesting that any attempt to increase mean birthweight in South Asians would markedly increase their fatness. Objective Our objective was to examine whether differences in cord leptin values between White British and Pakistani infants vary by birthweight category. Method We examined the difference in cord leptin levels between 659 White British and 823 Pakistani infants recruited to the Born in Bradford cohort study, by clinical categories and thirds of the birthweight distribution. Results Pakistani infants had a lower mean birthweight but higher cord leptin levels than White British infants [ratio of geometric mean (RGM) of cord leptin adjusted for birthweight = 1.36 (95% CI 1.26, 1.46)]. Birthweight was positively associated with cord leptin levels in both groups, with no evidence that the regression lines in the two groups diverged from each other with increasing birthweight. The relative ethnic difference in cord leptin was similar in low (<2500 g), normal and high (≥4000 g) birthweight infants (P-value for interaction = 0.91). It was also similar across thirds of the birthweight distribution [RGM (95% CI) in lowest, mid and highest thirds were 1.37 (1.20, 1.57), 1.36 (1.20, 1.54) and 1.31 (1.16, 1.52), respectively, P-interaction = 0.51]. Conclusions We found marked differences in cord leptin levels between Pakistani and White British infants but no evidence that this difference increases with increasing birthweight.

Differences in socioeconomic position, lifestyle and health-related pregnancy characteristics between Pakistani and White British women in the Born in Bradford prospective cohort study: the influence of the woman's, her partner's and their parents’ place of birth

Objective To examine differences between Pakistani and White British women in relation to socioeconomic position, lifestyle and health-related pregnancy characteristics, and to determine whether these differences vary depending on the womans, her partners and both of their parents’ place of birth. Design Prospective cohort study. Setting Bradford, UK Participants 3656 Pakistani and 3503 White British women recruited to the Born in Bradford study. Main outcome measures Socioeconomic position (employment status; level of education; receipt of benefits; housing tenure), lifestyle characteristics (body mass index (BMI) at the start of pregnancy; smoking during pregnancy) and health-related pregnancy characteristics (hypertensive disorders of pregnancy; gestational diabetes; fasting glucose, postload glucose and fasting insulin at ∼27 weeks gestation). Results Fewer Pakistani women were employed (OR 0.17, 95% CI 0.15 to 0.19), the difference being markedly less for UK born women. UK born Pakistani women were more likely, and South Asian born less likely, to be educated post 16 than White British women. Smoking was uncommon among Pakistani women, though the difference comparing UK born Pakistani women to White British women was less than for other groups. BMI was lower among Pakistani compared to White British women (adjusted mean difference −1.12, 95% CI −1.43 to −0.81), the difference being greatest when partners were UK born irrespective of the woman’s place of birth. Pakistani women had higher fasting and postload glucose (mean difference 0.20 mmol/L, 95% CI 0.17 to 0.24; 0.37, 95% CI 0.28 to 0.45), higher fasting insulin and were more likely to have gestational diabetes (GDM). Conclusions Our results suggest that some socioeconomic, lifestyle and pregnancy characteristics could be beginning to change in response to migration to the UK, with generally beneficial changes, that is, improving education and employment prospects, lower BMI and no evidence that being UK born has further increased the risk of GDM, but some negative, that is, slight increases in smoking.

Sleep Duration and Adiposity in Early Childhood: Evidence for Bidirectional Associations from the Born in Bradford Study

Study Objectives: To examine independent associations of sleep duration with total and abdominal adiposity, and the bidirectionality of these associations, in a young biethnic sample of children from a disadvantaged location. Methods: Child sleep duration (h/day) was parent‐reported by questionnaire and indices of total (body weight, body mass index, percent body fat (%BF), sum of skinfolds) and abdominal adiposity (waist circumference) were measured using standard anthropometric procedures at approximately 12, 18, 24, and 36 months of age in 1,338 children (58% South Asian; 42% White). Mixed effects models were used to quantify independent associations (expressed as standardised &bgr;‐coefficients (95% confidence interval (CI)) of sleep duration with adiposity indices using data from all four time‐points. Factors considered for adjustment in models included basic demographics, pregnancy and birth characteristics, and lifestyle behaviours. Results: With the exception of the sum of skinfolds, sleep duration was inversely and independently associated with indices of total and abdominal adiposity in South Asian children. For example, one standard deviation (SD) higher sleep duration was associated with reduced %BF by ‐0.029 (95% CI: −0.053, −0.0043) SDs. Higher adiposity was also independently associated with shorter sleep duration in South Asian children (for example, %BF: &bgr; = ‐0.10 (‐0.16, ‐0.028) SDs). There were no significant associations in White children. Conclusions: Associations between sleep duration and adiposity are bidirectional and independent among South Asian children from a disadvantaged location. The results highlight the importance of considering adiposity as both a determinant of decreased sleep and a potential consequence.

Smaller kidney size at birth in South Asians: findings from the Born in Bradford birth cohort study

BACKGROUND Rates of advanced chronic kidney disease and renal replacement therapy are higher in South Asian than in white British populations. Low birth weight is also more frequent in South Asian populations and has been associated with increased risks of kidney disease, perhaps due to a reduced nephron endowment. METHODS Using ultrasound scans at 34 weeks of gestation, we measured fetal kidney dimensions (transverse and anteroposterior diameters, length and circumference) and derived volume in a random sample of 872 white British and 715 South Asian participants in the Born in Bradford cohort study. Kidney measurements were compared between ethnic groups. RESULTS Birth weight for gestational age at 40 weeks was 200 g less in South Asian babies compared with white British babies. The mean kidney volume for gestational age was 16% lower in South Asian than in white British babies [8.79 versus 10.45 cm(3), difference 1.66 cm(3) (95% confidence interval 1.40-1.93, P < 0.001)]. The difference was robust after adjustment for maternal age, socio-economic factors, marital status, body mass index, smoking and alcohol use in pregnancy, parity, babys gender and birth weight for gestational age [adjusted difference 1.38 cm(3) (0.97-1.84), P < 0.001]. There were smaller reductions in other fetal measures. CONCLUSION South Asian babies have smaller kidneys compared with white British babies, even after adjusting for potential confounders including birth weight. This finding may contribute to increased risks of adult kidney disease in South Asian populations.

Commentary: Time to screen for, and treat, gestational diabetes

Gestational diabetes mellitus affects 2–9% of pregnancies1,2 and is associated with increased perinatal complications, but many expert committees, including the UK National Institute for Clinical Excellence (NICE),3 advise against routine screening on the grounds that it is of unproven effectiveness.4,5 This must now change with publication of the Australasian Carbohydrate Intolerance Study (ACHOIS).6 In this well-conducted trial pregnant women were screened between 24 and 34 weeks of gestation by a 50-g oral glucose challenge test (OGCT) with 1 hour glucose above 7.8 mmol/L followed by a 75-g formal glucose tolerance test (GTT). One thousand women with a fasting glucose less than 7.8 mmol/L and a 2-hour glucose between 7.8 and 11 mmol/L on the GTT were randomised to intervention or control groups. When the trial was designed these levels fulfilled the WHO criteria for impaired glucose tolerance.7 The intervention group had dietary advice, regular assessment of blood glucose and insulin as required to keep pre-prandial and 2-hour post-prandial glucose levels below 5.5 and 7 mmol/L, respectively. Women in the control group were told they did not have gestational diabetes, as indeed they did not under the old nomenclature. Their caregivers were told to treat them as if screening had not been done (i.e. further testing for gestational diabetes was only done for clinical indications). All women were followed up and analysis was by intention to treat. The primary outcome measure, a composite of serious perinatal complications (death, shoulder dystocia, bone fracture and nerve palsy), was dramatically lower in the intervention arm (1% vs 4%; relative risk 0.33; 95% confidence interval 0.14–0.75). All eight ‘avoidable’ adverse outcomes (four deaths, three nerve palsies and one fracture) were in the control arm. The intervention arm had more induced labours (39% vs 29%) and neonatal admissions (71% vs 61%), a similar rate of caesarean section (31% vs 32%) and a marked reduction in birthweight over 4 kg (10% vs 21%). Overall, 34 women needed treating to prevent one serious perinatal complication. These are dramatic benefits among women with relatively mild disease; after all women with the old definition of gestational diabetes, 2-hour glucose over 11 mmol/L, had been excluded. For the first time there is demonstrable clinical validity to screening for gestational diabetes on the basis of improved obstetric outcomes. The challenge is how to provide such screening and treatment. There is debate on how to screen for gestational diabetes and whether entire populations should be screened.8 There remain some differences in the values used for a diagnosis of gestational diabetes after an oral glucose tolerance test and these can influence population incidences.9 Strategies other than that described in the ACHOIS study have been proposed to select and treat women with glucose intolerance.10,11 There are ongoing studies that may be able to better define perinatal risk.12 ACHOIS supports formal screening between 28 and 34 weeks of gestation and demonstrates that conventional management strategies improve meaningful outcomes. Obstetricians must now respond to the challenge of providing such a service that might result, in a unit where 4000 women give birth, in 200 pathological pregnancies requiring complex multidisciplinary care. j