Biomedical subjects

S van Buuren

Publications and source records attributed to S van Buuren.

At least 19 recordsLinked to original sources

PubMed2005

Individual growth curve models for assessing evidence-based referral criteria in growth monitoring.

The goal of this study is to assess whether a growth curve model approach will lead to a more precise detection of Turner sydnrome (TS) than conventional referral criteria for growth monitoring. The Jenss-Bayley growth curve model was used to describe the process of growth over time. A new screening rule is defined on the parameters of this growth curve model, parental height and gestational age. The rule is applied to longitudinal growth data of a group of children with TS (n=777) and a reference (n=487) group. The outcome measures are sensitivity, specificity and median referral age. Growth curve parameters for TS children were different from reference children and can therefore be used for screening. The Jenss-Bayley growth model, which uses all longitudinal measurements from birth to a maximum age of 5 years with at least one measurement after the age of 2, together with parental height and gestational age can achieve a sensitivity of 85.2 per cent with a specificity of 99.5 per cent and a median referral age of 4.2 (the last measurement between the age of 2 and 5 of each child is considered to be the moment of referral). Sensitivity increases by 2 percentage points when decreasing the specificity to 99 per cent. The Jenss-Bayley growth model from birth to a maximum age of 8 years with at least one measurement after the age of 2, together with parental height results in a sensitivity of 89.0 per cent with a specificity of 99.5 per cent and a median referral age of 6.1. For a specificity of 98 per cent, we obtain a sensitivity of 92.3 per cent. In comparison to conventional rules applied to the same data, sensitivity is about 11-30 percentage points higher at the same level of specificity for the Jenss-Bayley growth rule. We conclude that from the age of 4, growth curve models can improve the screening on TS to conventional screening rules.

Biometry↗

PubMed2005

Catch-up growth in Malawian babies, a longitudinal study of normal and low birthweight babies born in a malarious endemic area.

INTRODUCTION: Infant growth has not been studied in developing countries in relation to maternal factors related to malaria in pregnancy and maternal illiteracy. OBJECTIVE: To describe growth patterns in infants with low and normal birthweight and determine maternal risk factors for infant undernutrition. METHODS: Babies born in a rural district of southern Malawi were recruited. An infant cohort was selected on the basis of low or normal birthweight. Weight and length were recorded at birth and at 4-weekly intervals until at 52 weeks after birth. Maternal characteristics at first antenatal attendance and delivery were obtained. Odds ratios in univariate analysis were adjusted for birthweight. Factors included in the multivariate regression included maternal illiteracy, season of birth, maternal iron deficiency and number of infant illness episodes. RESULTS: Low birthweight infants were shorter and lighter throughout infancy than either normal birthweight or international reference values. At 12 months, placental or peripheral malaria at delivery (adjusted odds 1.8; 1.0, 3.1), number of infant illness episodes (AOR = 2.1; 1.2, 3.6) and maternal illiteracy (AOR = 2.7; 1.5, 4.9) were independently associated with low weight for age. Maternal short stature (AOR = 1.8; 1.1. 3.2), male sex (AOR = 2.4; 1.4, 4.1), number of infant illness episodes (AOR = 2.6; 1.5, 4.4), and birth in the rainy season (2.1; 1.2, 3.7) were independently associated with stunting. Placental or peripheral malaria at delivery (AOR = 2.2; 1.1, 4.4) and number of illness episodes (AOR = 2.2; 1.1, 4.5) were independently associated with thinness. CONCLUSION: Malaria during pregnancy and maternal illiteracy are important maternal characteristics associated with infant undernutrition. Innovative health/literacy strategies are required to address malaria control in pregnancy in order to reduce the magnitude of its effects on infant undernutrition.

Body Height↗

PubMed2005

Nationwide age references for sitting height, leg length, and sitting height/height ratio, and their diagnostic value for disproportionate growth disorders.

AIMS: To obtain age references for sitting height (SH), leg length (LL), and SH/H ratio in the Netherlands; to evaluate how SH standard deviation score (SDS), LL SDS, SH/H SDS, and SH/LL SDS are related to height SDS; and to study the usefulness of height corrected SH/H cut-off lines to detect Marfan syndrome and hypochondroplasia. METHODS: Cross-sectional data on height and sitting height were collected from 14,500 children of Dutch origin in the age range 0-21 years. Reference SD charts were constructed by the LMS method. Correlations were analysed in three age groups. SH/H data from patients with Marfan syndrome and genetically confirmed hypochondroplasia were compared with height corrected SH/H references. RESULTS: A positive association was observed between H SDS, SH SDS, and LL SDS in all age groups. There was a negative correlation between SH/H SDS and height SDS. In short children with a height SDS <-2 SDS, a cut-off limit of +2.5 SD leads to a more acceptable percentage of false positive results. In exceptionally tall children, a cut-off limit of -2.2 SDS can be used. Alternatively, a nomogram of SH/H SDS versus H SDS can be helpful. The sensitivity of the height corrected cut-off lines for hypochondroplasia was 80% and for Marfan syndrome only 30%. CONCLUSIONS: In exceptionally short or tall children, the dependency of the SH/H ratio (SDS) on height SDS has to be taken into consideration in the evaluation of body proportions. The sensitivity of the cut-off lines for hypochondroplasia is fair.

Adolescent↗

PubMed2005

Anthropometry of fetal growth in rural Malawi in relation to maternal malaria and HIV status.

OBJECTIVE: To describe fetal growth centiles in relation to maternal malaria and HIV status, using cross sectional measurements at birth. DESIGN: A cross sectional study of pregnant women and their babies. Data on maternal socioeconomic status and current pregnancy, including HIV status and newborn anthropometry, were collected. Malaria parasitaemia was assessed in maternal peripheral and placental blood, fetal haemoglobin was measured in cord blood, and maternal HIV status was determined. SETTING: Two district hospitals in rural southern Malawi, between March 1993 and July 1994. OUTCOME VARIABLES: Newborn weight, length, Rohrer's ponderal index. RESULTS: Maternal HIV (adjusted odds ratio (AOR) 1.76 (95% confidence interval 1.04 to 2.98)) and first pregnancy (AOR 1.83 (1.10 to 3.05)) were independently associated with low weight for age. Placental or peripheral parasitaemia at delivery (AOR 1.73 (1.02 to 2.88)) and primigravidae (AOR 2.13 (1.27 to 3.59)) were independently associated with low length for age. Maternal malaria at delivery and primiparity were associated with reduced newborn weight and length but not with disproportionate growth. Maternal HIV infection was associated only with reduced birth weight. The malaria and parity effect occurred throughout gestational weeks 30-40, but the HIV effect primarily after 38 weeks gestation. CONCLUSION: Fetal growth retardation in weight and length commonly occurs in this highly malarious area and is present from 30 weeks gestation. A maternal HIV effect on fetal weight occurred after 38 weeks gestation.

Birth Weight↗

PubMed2004

[Body-mass index cut-off values for underweight in Dutch children].

OBJECTIVE: To determine the cut-off values for the body-mass index (BMI) for underweight and serious underweight in children up to 18 years of age based on the Dutch growth standards of 1980, and to determine the prevalence of underweight and serious underweight in the 1997 Dutch growth-study figures. DESIGN: Secondary data analysis. METHOD: Cut-off values for underweight were determined by first calculating the percentage of 18-years old with a BMI < 18.5 kg/m2 in 1980, followed by a calculation of the BMI at younger ages under which the same percentage fell. Serious underweight in 18-year olds was defined as a BMI < 17.0 kg/m2. RESULTS: Between 1980 and 1997 the prevalence of serious underweight increased in children aged between 2 and 6 years from 1.5% to 3.6% and from 2.9% to 3.3%, in boys and girls respectively. In older children (7-18 years) the prevalence decreased from 1.5% to 1.4% for boys and from 2.9% to 1.7% for girls. CONCLUSION: Not only did the median weight of the population increase between 1980 and 1997, but there was also a rise in the variation of the weights at any given age. The latter could reflect more marked health differences.

Adolescent↗

PubMed2004

Height, weight, body mass index and pubertal development references for children of Moroccan origin in The Netherlands.

AIM: To provide growth and sexual maturation reference data for Moroccan children living in The Netherlands and to compare them with the reference data of children of Dutch origin. METHODS: Cross-sectional growth and demographic data were collected from 2880 children of Moroccan origin and 14,500 children of Dutch origin living in The Netherlands in the age range 0-20 y. Growth references for length, height, weight, weight-for-height, body mass index (BMI) and head circumference were constructed with the LMS method. Predictive variables for height and BMI were assessed by regression analyses. Reference curves for sexual maturation were estimated by a generalized additive model. RESULTS: Moroccan young adults were on average 9 cm shorter than their Dutch contemporaries. Mean final height was 174.7 cm for males and 161.3 cm for females. Height differences in comparison with Dutch children increase from 2 y onwards. Height SDS was predominantly associated with target height. Compared to Dutch children, maturation started 0.2 and 0.9 y later for girls and boys, respectively. Median age at menarche was 12.9 y, 3.6 mo earlier than in Dutch girls (p = 0.001). BMI of Moroccan children was above that of Dutch children, especially for girls. BMI SDS was associated with birthweight in the age group 0 - < or = 5 y. CONCLUSION: Moroccan children living in The Netherlands are substantially shorter than Dutch children. Girls have higher weight-for-height and BMI for age. Median age at menarche occurs earlier. Given these differences, separate growth charts for the Moroccan children are useful.

Adolescent↗

PubMed2004

Towards evidence based referral criteria for growth monitoring.

AIMS: To evaluate the performance of growth monitoring in detecting diseases. Turner's syndrome (TS) is taken as the target disease. METHODS: Case-control simulation study. Three archetypal screening rules are applied to longitudinal growth data comparing a group with TS versus a reference group from birth to the age of 10 years. Main outcome measures were sensitivity, specificity, and median referral age. RESULTS: Clear differences in performance of the rules were found. The best rule takes parental height into account. Combining rules could improve diagnostic accuracy. CONCLUSION: Growth monitoring is useful to screen for TS. A combined rule that takes absolute height SDS, parental height, and deflection in height velocity into account is the best way to do this. Similar research is needed for other diseases, populations, and ages, and the results should be synthesised into evidence based referral criteria.

Body Height↗

PubMed2004

Many referrals under Dutch short stature guidelines.

The number of referrals under strict adherence to the Dutch consensus guidelines for short stature was estimated using longitudinal data from 970 children (0-10 years). Results showed that over 38% of all children would have to be referred one or more times. There is therefore a clear need to revise the current guidelines.

Body Height↗

PubMed2003

Unidimensionality and reliability under Mokken scaling of the Dutch language version of the SF-36.

The sub-scales of the SF-36 in the Dutch National Study are investigated with respect to unidimensionality and reliability. It is argued that these properties deserve separate treatment. For unidimensionality we use a non-parametric model from item response theory, called the Mokken scaling model, and compute the corresponding scalability coefficients. We estimate reliability under the Mokken model, assuming that the items are double homogeneous, and compare it to Cronbach's alpha. The scalability of the sub-scale general health perceptions is medium (H = 0.46), and for the other sub-scales it is strong (H > or = 0.6). The reliability in terms of alpha indicates that all sub-scales can be used in basic research (alpha > 0.70), but that only physical functioning can be used for clinical applications of quality of life (alpha > 0.90). The relative merits of our approach are discussed.

Humans↗

PubMed2003

Assessing comparability of dressing disability in different countries by response conversion.

BACKGROUND: Comparability of health data is a major challenge within the context of the Health Monitoring Programme of the European Commission. A common problem in surveys is that many variations of essentially the same question exist. METHODS: Response conversion is a new method for improving comparability by scaling the data onto a common scale. Comparisons between member states can then be made in terms of the common scale. A first step is the construction of a conversion key. This is a relatively complex activity, but needs to be done only once. The second step is the actual data transformation. This is simple, and can be repeatedly done on a routine basis as new information arrives. Construction of the key is only possible if enough overlapping information can be found. RESULTS: The method is illustrated for dressing disability from five European countries. Differences occur between countries, between sexes and between age groups. These were similar in magnitude. CONCLUSION: Response conversion is a new method for enhancing comparability among existing data. Conversion can only be done if a key is available. More work is needed to establish the technique. Future implications within the Health Monitoring Programme are discussed.

Activities of Daily Living↗

PubMed2001

[Increased prevalence of overweight and obesity in Dutch children, and the detection of overweight and obesity using international criteria and new reference diagrams].

OBJECTIVE: To determine the prevalence of overweight and obesity in Dutch children in 1980 and 1997 according to international criteria, and to design new reference diagrams for overweight and obesity in children. DESIGN: Descriptive. METHOD: The prevalence of overweight and obesity, based on height and weight data from the Fourth Dutch Growth Study (1997), was determined according to international criteria for age and sex. RESULTS: In 1997, the prevalence of overweight and obesity increased in both boys and girls compared to 1980: in 1997, the prevalence of overweight ranged between 7.1 and 15.5% for boys, and between 8.2 and 16.1% for girls. Both the prevalence of overweight and obesity was higher in girls than in boys. CONCLUSION: By applying the international criteria for overweight and obesity and reference growth diagrams based upon the 1997 Dutch growth study, the prevention and detection of overweight and obesity has to be implemented with vigour in Dutch youth health care.

Adolescent↗

PubMed2001

Worm plot: a simple diagnostic device for modelling growth reference curves.

The worm plot visualizes differences between two distributions, conditional on the values of a covariate. Though the worm plot is a general diagnostic tool for the analysis of residuals, this paper focuses on an application in constructing growth reference curves, where the covariate of interest is age. The LMS model of Cole and Green is used to construct reference curves in the Fourth Dutch Growth Study 1997. If the model fits, the measurements in the reference sample follow a standard normal distribution on all ages after a suitably chosen Box-Cox transformation. The coefficients of this transformation are modelled as smooth age-dependent parameter curves for the median, variation and skewness, respectively. The major modelling task is to choose the appropriate amount of smoothness of each parameter curve. The worm plot assesses the age-conditional normality of the transformed data under a variety of LMS models. The fit of each parameter curve is closely related to particular features in the worm plot, namely its offset, slope and curvature. Application of the worm plot to the Dutch growth data resulted in satisfactory reference curves for a variety of anthropometric measures. It was found that the LMS method generally models the age-conditional mean and skewness better than the age-related deviation and kurtosis.

Adolescent↗

PubMed2001

Revision of the ICIDH Severity of Disabilities Scale by data linking and item response theory.

The Severity of Disabilities Scale (SDS) of the ICIDH reflects the degree to which an individual's ability to perform a certain activity is restricted. This paper describes the application of two models from item response theory (IRT), the graded response model and the partial credit model, in order to derive a tentative proposal for a revised SDS. The key ingredient of the approach is to scale existing disability items obtained in different studies on a common scale by exploiting the overlap. Both IRT models are fitted to a linked data set containing items for measuring walking disability. Based on these solutions, a tentative SDS is constructed. The paper concludes with a discussion of the implications, limitations and advantages of the approach.

Activities of Daily Living↗

PubMed2001

An analysis of intra-uterine growth retardation in rural Malawi.

OBJECTIVE: (1) To describe the sex-specific, birth weight distribution by gestational age of babies born in a malaria endemic, rural area with high maternal HIV prevalence; (2) to assess the contribution of maternal health, nutritional status and obstetric history on intra-uterine growth retardation (IUGR) and prematurity. METHODS: Information was collected on all women attending antenatal services in two hospitals in Chikwawa District, Malawi, and at delivery if at the hospital facilities. Newborns were weighed and gestational age was assessed through post-natal examination (modified Ballard). Sex-specific growth curves were calculated using the LMS method and compared with international reference curves. RESULTS: A total of 1423 live-born singleton babies were enrolled; 14.9% had a birth weight <2500 g, 17.3% were premature (<37 weeks) and 20.3% had IUGR. A fall-off in Malawian growth percentile values occurred between 34 and 37 weeks gestation. Significantly associated with increased IUGR risk were primiparity relative risk (RR) 1.9; 95% CI 1.4--2.6), short maternal stature (RR 1.6; 95% CI 1.0--2.4), anaemia (Hb<8 g/dl) at first antenatal visit (RR 1.6; 95% CI 1.2--2.2) and malaria at delivery (RR 1.4; 95% CI 1.0--1.9). Prematurity risk was associated with primiparity (RR 1.7; 95% CI 1.3--2.4), number of antenatal visits (RR 2.2; 95% CI 1.6--2.9) and arm circumference <23 cm (RR 1.9; 95% CI 1.4--2.5). HIV infection was not associated with IUGR or prematurity. CONCLUSION: The birth-weight-for-gestational-age, sex-specific growth curves should facilitate improved growth monitoring of newborns in African areas where low birth weight and IUGR are common. The prevention of IUGR requires improved malaria control, possibly until late in pregnancy, and reduction of anaemia.

Anemia, Iron-Deficiency↗

PubMed2001

Pubertal development in The Netherlands 1965-1997.

We investigated pubertal development of 4019 boys and 3562 girls >8 y of age participating in a cross-sectional survey in The Netherlands and compared the results with those of two previous surveys. Reference curves for all pubertal stages were constructed. The 50th percentile of Tanner breast stage 2 was 10.7 y, and 50% of the boys had reached a testicular volume of 4 mL at 11.5 y of age. Median age at menarche was 13.15 y. The median age at which the various stages of pubertal development were observed has stabilized since 1980. The increase of the age at stage G2 between 1965 and 1997 is probably owing to different interpretations of its definition. The current age limits for the definition of precocious are close to the third percentile of these references. A high agreement was found between the pubic hair stages and stages of pubertal (genital and breast) development, but slightly more in boys than in girls. Menarcheal age was dependent on height, weight, and body mass index. At a given age tall or heavy girls have a higher probability of having menarche compared with short or thin girls. A body weight exceeding 60 kg (+1 SDS), or a body mass index of >20 (+1 SDS), has no or little effect on the chance of having menarche, whereas for height such a ceiling effect was not observed. In conclusion, in The Netherlands the age at onset of puberty or menarche has stabilized since 1980. Height, weight, and body mass index have a strong influence on the chance of menarche.

Adolescent↗

PubMed2000

[Cesar therapy is temporarily more effective in patients with chronic low back pain than the standard treatment by family practitioner: randomized, controlled and blinded clinical trial with 1 year follow-up].

OBJECTIVE: To determine the effectiveness of a special form of exercise therapy ('Cesar therapy') on self reported recovery and improvement of posture amongst patients with chronic aspecific lower back pain. DESIGN: Prospective randomized controlled and blinded investigation. METHOD: After informed consent had been obtained, patients with chronic aspecific lower back pain were given, on a randomized basis, either an exercise therapy (experimental group, n = 112) or a standard treatment by their general practitioner (control group, n = 110). Outcome measures were self reported recovery of back pain and improvement of posture (thoracic and lumbar spine, pelvis). Self reported recovery was determined by means of a dichotomized 7-point scale (questionnaire). Posture was measured qualitatively by a panel of 11 Cesar therapists (blinded) and quantitatively by an optical-electronic posture recording system (Vicon). Measurements were taken at baseline (pre-randomization) and at 3, 6 and 12 months after randomization. RESULTS: Three months after randomization, patients who were treated according to Cesar therapy, reported an improvement in their back symptoms (80%) significantly more often than the control group (47%). In both groups, however, only small improvements in posture were found. The judgement of the Cesar panel exhibited a significant difference between the two groups, with respect to the spine, in favour of Cesar therapy. Differences between the groups were still present 6 months after randomization, but could no longer be detected at 12 months after randomization. CONCLUSION: Cesar therapy was significantly more effective than standard treatment among patients with chronic lower back pain for a period of 6 months after randomization.

Adult↗

PubMed2000

Body index measurements in 1996-7 compared with 1980.

OBJECTIVES: To compare the distribution of body mass index (BMI) in a national representative study in The Netherlands in 1996-7 with that from a study in 1980. METHODS: Cross sectional data on height, weight, and demographics of 14 500 boys and girls of Dutch origin, aged 0-21 years, were collected from 1996 to 1997. BMI references were derived using the LMS method. The 90th, 50th, and 10th BMI centiles of the 1980 study were used as baseline. Association of demographic variables with BMI-SDS was assessed by ANOVA. RESULTS: BMI age reference charts were constructed. From 3 years of age onwards 14-22% of the children exceeded the 90th centile of 1980, 52-60% the 50th centile, and 92-95% the 10th centile. BMI was related to region, educational level of parents (negatively) and family size (negatively). The -0.9, +1.1, and +2.3 SD lines in 1996-7 corresponded to the adult cut off points of 20, 25, and 30 kg/m(2) recommended by the World Health Organisation/European childhood obesity group. CONCLUSION: BMI age references have increased in the past 17 years. Therefore, strategies to prevent obesity in childhood should be a priority in child public health.

Adolescent↗

PubMed2000

Continuing positive secular growth change in The Netherlands 1955-1997.

Since 1858, an increase of mean stature has been observed in the Netherlands, reflecting the improving nutritional, hygienic, and health status of the population. In this study, stature, weight, and pubertal development of Dutch youth, derived from four consecutive nationwide cross-sectional growth studies during the past 42 y, are compared to assess the size and rate of the secular growth change. Data on length, height, weight, head circumference, sexual maturation, and demographics of 14,500 boys and girls of Dutch origin in the age range 0-20 y were collected in 1996 and 1997. Growth references for height and weight were constructed with a method that summarizes the distribution by three smooth curves representing skewness (L curve), the median (M curve), and coefficient of variation (S curve). The relationship between height and demographic variables was assessed by multivariate analysis. Reference curves for menarche and secondary sex characteristics were estimated by a generalized additive model using a logit transformation. A positive secular growth change has been present in the past 42 y for children, adolescents, and young adults of Dutch origin, although at a slower rate in the last 17 y. Height differences according to region, educational level of child and parents, and family size have remained. In girls, median age at menarche has decreased by 6 mo during the past four decades to 13.15 y. Environmental conditions have been favorable for many decades in the Netherlands, and the positive secular change in height has not yet come to a halt, in contrast to Scandinavian countries. Main contributors to the increase in height may be improved nutrition, child health, and hygiene, and a reduction of family size.

Adolescent↗