About the Bergen Growth Study
Barneklinikken, Haukeland Universitetssykehus, Bergen; Institutt for klinisk medisin, seksjon for pediatri, Universitetet I Bergen, Bergen
Vrije Universiteit Brussel, Laboratory for Anthropogenetics, Brussel, Belgia
Geir Egil Eide
Centre for Clinical Research, Haukeland University Hospital, Bergen
Bente Brannsether Ellingsen
Stavanger University Hospital, Stavanger
Department of Public Health and Primary Health Care, University of Bergen
Department of Growth and Reproduction, Rigshospitalet, University of Copenhagen, Denmark
Children’s growth and development is dynamic and is at some level reflecting the environment. Secular trends in children’s length growth and final height has been described over the last hundred years and reflects improved job satisfaction, improved nutrition and fewer infections (1). Updated knowledge about growth and growth parameters is important for all health-related work with children and adolescents, both in order to follow up the child, and to follow trends in the child population. On an individual basis this applies to issues such as low or high altitude, abnormal body proportions, pubs minority, as well as over-or under-weight. The population base is including the question of whether there are adverse changes in weight in the child population that should trigger social measures.
The first Norwegian growth curves were constructed by Sundal on the basis of measurements of head circumference performed in Oslo in 1949 (2), and measurement of height and weight collected in Bergen in the period 1950-6 (3). In 1971-4 Waaler followed this up with a study of 3-17 year old children in Bergen, which formed the basis for the current percentile curve for length, weight and head circumference in children older than 4 years (4, 5). The current references for children aged 0-4 years from the SYSBARN- survey conducted in Oslo and Hedmark in 1982-4, and data from the Medical Birth Registry (6). The current Norwegian references are based on measurements performed 23-36 years ago.
There has been a worrying increase of overweight and obesity in recent decades in developed countries, a trend that is also now seen in developing countries. The prevalence of obesity has 2-3 doubled in the last years in the U.S. and Europe and it is now between 12% and 20% in children aged 7-11 years in Northern and Western European countries (7, 8, 9) Obesity is already a serious problem in childhood and child obesity is related to increased morbidity and mortality in adulthood (10, 11, 12).
The increase in the number of children with overweight and obesity demonstrates the importance of good clinical tools to assess overweight and obesity. Todayâs references has only the weight-against-height curves, but now body mass index (body mass index, kg/m2 (BMI)) has been internationally recommended for use to assess the degree of overweight and obesity. BMI curves for children and the youth population have been missing in Norway, but are now made for the first time under the direction of the Bergen growth study.
1. Provide information on length / height and body proportions. The latter involves measurements of sitting height, arm-spen, head circumference, forearm length and leg length.
2. Provide information on overweight and obesity in Norwegian children and adolescents, to compare measurements of body mass index, skin folds and stomach size.
3. Provide information on growth rate.
4. Identify factors that can affect growth and weight development in Norwegian children.
5. Designing clinically relevant percentile / SD curves for a range of growth parameters
MATERIALS AND METHODS
A. Cross-sectional survey to assess growth and weight parameters. This was conducted from November 2003 to December 2006. The following measurements were made:
# Length / height and weight among children 0-19 years old
# head circumference I0-15 years old children
# Sitting height and leg size in 4-19 year old children
# Arms Penn, skin folds, underarm and leg-length in children 4-15 years old.
B. Longitudinal study to determine growth rate. About half the children aged 6-18 were measured one year later, then only measurement of height and weight. Data collection was conducted in the period 2004-2006.
C. C. Identification of factors that can affect growth and weight development. Parts of this study involved performing a survey and forwarding the data to existing databases. The survey was conducted in 2006 and 2007. The response rate was 67%. The survey contains 38 questions to all parents who had children aged less than 15 years at the time of measurement.
D. Design of clinically relevant growth curves.
Cross-sectional survey was conducted from November 2003 to December 2006 when a total of 8312 children aged 0-19 years were included and measured. The children were recruited from the Bergen based on stratified random selection of health clinics (n = 8), day care centers (n = 34) and schools (n = 24, including 19 primary and or secondary schools and 5 high schools). All children were invited to participate, but only children where there was a written consent from parents and / or children to participate, were measured. At health centers, around 98% of available children were measured. Participation rate was 57% in kindergarten, 69% in primary schools (1st-7. age groups), 53% in secondary schools (8th-10. step) and in upper secondary schools (1st-3rd. increments). Part- time in kindergarten, activities in the kindergarten or school measure days and travel and sickness absence were all factors that influenced the attendance in addition to the fact that some did not want to participate.
The children were measured by public health nurses employed in the study of health centers, while children in kindergartens and schools were measured by study nurses who work in teams, two and two together. Measurements, performed between 08.30 and 13.00, were recorded directly onto laptop computers.
Surface length was measured up to two years of age with Harpenden Infant Measuring Table. The children were measured naked, but with panties and t-shirts on. The head was held by parents up to the head plate, so that the lower edge of orbit stayed in line with the ear opening. Both legs were extended by the school nurse, and the movable plate led to the soles.
At two years of age height was measured standing using the Holtain Portable Stadiometer. The children were measured naked, but with panties and t-shirts on. The measurements were performed without shoes and socks to make sure foot suspension was appropriate and heals were not lifted from the floor. The children were measured with the feet together and with heal buttocks and shoulders into the meter. If the hair was thick, a light pressure was applied to the head plate. The children were asked to “stand straight” and the measurements were taken during normal respiration. Head position was such that the lower edge of orbit stayed in horizontal line with the ear opening.
Weight was measured at the clinic without a nappy using a digital infant weight (Seca). In kindergartens and schools weight was measured wearing panties, occasionally bra, using a digital weight (Seca).
When measuring the head circumference, the greatest head circumference was measured with a metal measuring tape, (Lufkin).
At the start of each measuring day, measuring equipment, height and length measure were checked. Person weights at health centers were checked twice a year and at school or in Kindergarten every time they were moved (to a new school / kindergarten). Twice a year, all the performers would meet at a common training session. 10 children were measured twice by all the performers. Measurement accuracy was assessed as well as the variation between the meters.
Calculations of sample size were performed on the basis of the statistical strength.
Percentile curves were prepared using the LMS method (14). The data is also analyzed with the software programs SPSS, STAT, and R.
RELEVANT MAIN RESULTS
1. Increase in weight against height in children and adolescents (15).
Amongst children aged 4-16 years, the prevalence of overweight and obesity 12.5% and 2.1% in boys and 14.8% and 2.9% in girls (cf. IOTF-cut-offs). Compared with figures from the 1970s years is 8% of boys and 7.2% of girls of 97.5 – percentile of weight-for-height from 19771-4 (forstĂ„r ikke denne setningen..). The difference is greatest in the top percent missiles, while the lowest is unchanged. Growth increase limits therefore largely a subset of the Norwegian child population. The study also shows the increase in skin folds. Only ethnic Norwegian children were included in this analysis to make it comparable with the figures from the 1970s
2. New growth curves for Norwegian children aged 0-19 years (16)
On the basis of data from the Bergen growth study new percentile curves have been developed for ages 0-12 months (respectively, head circumference, length and weight against age) 1-5 years (respectively, head circumference, length / height and weight against age), 4-19 years (respectively, height and weight against age) and 2-19 (body mass index (BMI) for age). On the curves, a gray field that defines the area between the median 2.0 to 2.5 standard deviations (s) and the median area between -2.0 to -2.5 s are added. The BMI curve has specified limits for overweight, obesity and underweight. The new curves reflect the growth of Norwegian children of today and can replace the existing growth curves when growth and weight development is to be followed in primary- or specialist health services.
3. The new curves compared with the existing Norwegian reference (16).
In today’s children aged 0-4 years, the length / height and weight are only marginally changed from the existing growth curves. For older children, however there is an increase in the 50 percentile for height up to 3.4 cm in boys and 2.5 cm in girls. For children over 4 years, weight for height is also increased, particularly in the top percent missiles. Secular growth trends reflect the need for new growth curves.
4. The new growth curves compared with international growth curves of WHO for ages 0-5 years (16)
The curves of the current Norwegian children are above WHO curves for birth weight, length / height, weight and head circumference for age group 6 months to 5 years of age, which may reflect differences in the environment or growth potential between the populations.
5. Knudtzon J, Waaler PE, Skjaerven R, Solberg LK, Steen J. [New Norwegian percentage charts for height, weight and head circumference for age groups 0-17 years]. Tidsskr Nor LĂŠgeforen 1988;108:2125-35.
6. Knudtzon J, Waaler PE, Solberg LK, Grieg E, Skjaerven R, Steen J, et al. [Height, weight and head circumference of 0-4 year-old children. Data based on the SYSBARN registration and medical register of births]. Tidsskr Nor lĂŠgeforen 1988;108:2136-42.
12. Sayer AA, Syddall HE, Dennison EM, Gilbody HJ, Duggleby SL, Cooper C, et al. Birth weight, weight at 1 y of age, and body composition in older men: findings from the Hertfordshire Cohort Study. American J Clin Nutr 2004;80:199-203.
17. JĂșlĂusson PB, Roelants M, Hoppenbrouwers, Hauspie R, Bjerknes R. Growth of Belgian and Norwegian children compared to the WHO growth standards: prevalence below -2 andÂ >2 SD and the effect of breastfeeding. Arch Dis Child 2010 Jun 3. [Epub ahead of print].