PubMed Health⌕ Search

Biomedical subjects

J G Fryer

Publications and source records attributed to J G Fryer.

30 records · Page 2Linked to original sources
PubMed1987

Analysis of linear growth using a mathematical model. I. From birth to three years.

According to the "ICP-growth model" (ICP = Infancy, Childhood and Puberty components), linear growth during the first three years of life can be represented mathematically by a combination of a sharply decelerating Infancy component and a slowly decelerating Childhood component. Growth as measured by supine length is analysed for 191 longitudinally followed healthy infants using this model. The main aim is to devise ICP-based methods for biological and clinical applications. The onset of the Childhood component, which occurs some time between 6 and 12 months of age and is typically abrupt, can be detected on an individual basis. Its starting point probably defines the as yet unknown age at which growth hormone begins to exert a significant influence. The analyses have also revealed some new facets of linear growth. Most infants are found to have a non-linear decelerating Infancy component, free from seasonal influence. Age at onset of the Childhood component is earlier for girls than for boys and is positively related to the magnitude of the Infancy component. During the second year of life the variation in growth rate of the cohort increases. This fluctuation is found to be seasonal and greater for those with late onset of the Childhood component. During the third year of life the growth pattern is stabilized.

Age Factors↗
PubMed1987

Analysis of linear growth using a mathematical model. II. From 3 to 21 years of age.

The 'ICP growth model' (ICP = Infancy, Childhood and Puberty components) represents linear growth from 3 years of age to maturity by a combination of a slowly decelerating childhood component together with a sigmoid puberty component, the latter acting only during adolescence. Linear growth is analysed for 157 longitudinally followed healthy infants using this model. The main aim is to assess the ability of the ICP model to describe and evaluate individual growth patterns in healthy children with particular emphasis on the considerable individual variation in the timing of puberty and the shape of the pubertal growth spurt. The use of the model to evaluate growth longitudinally over both short and long periods is also outlined. Reference values based on the ICP approach, the ICP Standard, seem to have a number of advantages in comparison with cross-sectional standards. In the 'Prepubertal ICP Standard', the contribution of the puberty component is omitted. The standard can be applied on an individual basis to evaluate prepubertal growth and pubertal onset, independently of the timing of puberty. By using the 'Pubertal ICP Standard' both the difference in pubertal maturation and the negative relationship between the size of the pubertal gain and the timing of puberty are taken into account. The fact that the gain in the puberty component is time-invariant, and can thus be aligned with the timing of puberty for an individual child, forms the basis of this approach. The analyses have also revealed a new predictor for final height, which is termed HAPO (height adjusted for pubertal onset). This predictor is based on age and attained size at onset of puberty--the 'onset' regression line.

Adolescent↗
PubMed1985

A methodology for evaluating size at birth.

Data from the Swedish Medical Birth Registration, 1977-78, were utilized to develop methods of calculating reference standards for evaluating size at birth. Using the clinical information available, a 'healthy' sub-group was extracted. The individual distributions of birthweight (BW), birth length (BL) and birth headcircumference (BHc) at each week of gestational age (GA) were modelled following some truncation of their ranges. Application of the Box-Cox power family of transformations was generally found to improve the normality of the data. Certain percentages (such as 2.28, 50 and 97.72) were linked through a smoothing device. Features of the results include a positively skewed BW distribution in most GA weeks, a normal positively skewed BW distribution in most GA weeks, a normal distribution of BL and BHc at term, a larger relative variation in BW at lower GA than at term, and a distinct sigmoid shape of the median and other BW curves. Compared with five commonly quoted standards, the present data show the least deceleration in the fullterm region. Disregarding the clinical information, 'primary' sub-groups were also extracted using decomposing techniques. These gave rise to similar BW/GA relationships. Using data from the WHO comparative study, the method just mentioned was applied to standardize BW and BW-specific early neonatal mortality rates. This resulted in an improved description of biological events.

Birth Weight↗
PubMed1984

Factors associated with delayed onset of regular respiration.

In a population of 16333 singleton births born in one week of April, 1970, 4.4% failed to establish regular respiration within 3 min of birth. A follow-up at 5 years of age collected medical, educational and sociological information on 79.6% of the survivors of the cohort identified by the birth survey. Data have been analysed to investigate the relationships between the delay in the onset of regular respiration and possible risk factors identifiable prior to or at the time of birth. Complex statistical analysis employing linear modelling techniques showed that the delay in the onset of respiration was primarily related to: null and high parity; antepartum haemorrhage (especially placenta praevia); pre-eclampsia; breech delivery; Caesarian section and low birthweight. There was no association with maternal smoking during pregnancy or with social class. These conclusions are reasonably consistent with those drawn from other studies using alternative measures of asphyxia.

Child, Preschool↗
PubMed1984

Delayed onset of regular respiration and subsequent development.

A comprehensive survey carried out at birth, data on mortality and a 5 year follow-up covering medical, educational and sociological aspects of child development were available for singleton births born in one week of April 1970. The survey at 5 years of age included 12363 children, 79.6% of the surviving cohort. An assessment has been made of the extent to which delay in the onset of regular respiration at birth is associated with the subsequent development of the child. Using the results of our previous investigations, the relationships between this delay and other factors known at the time of birth have been taken into account. The distributions of a large number of development variables were not significantly different for groups of children determined by respiratory delay at birth, but there was an association with mortality and cerebral palsy. In addition, there was an unexpected relationship between delayed onset of respiration and subsequent bronchitis. This association remained significant after controlling for possible confounding effects using linear modelling techniques.

Bronchitis↗
PubMed1983

Plus ça change: predictors of birthweight in two national studies.

The 16 989 singleton births in one week of March, 1958, studied by the British Perinatal Mortality Survey, were subjected to an analysis of covariance, which showed that major factors associated with birthweight of the infant were: maternal height, history of smoking in pregnancy, parity and history of pre-eclampsia during the pregnancy. The same analysis was repeated on the data collected on 16792 singletons born 12 years later in one week of April, 1970 and studied by the British Births Survey. In spite of major changes in obstetric practice and in the maternal population, the same factors were shown to be highly significant and the magnitude of the associations had changed little.

Analysis of Variance↗
PubMed1975

Maximum likelihood estimation for a special type of grouped data with an application to a dose-response problem.

A short-cut method is given for calculating grouped maximum likelihood (ML) estimates when the data are relatively coarsely grouped in some directions, but more finely grouped in others. The algebraic details are then worked out for a dose-response problem that generates data of this kind. The situation envisaged is a variation on the usual quantal response problem in that dosage levels are taken to be random but grouped. Finally, the method is applied both to real and simulated response data conforming to this pattern and shown to work well in practice.

Birth Weight↗
PubMedDate not supplied

An update of the Swedish reference standards for weight, length and head circumference at birth for given gestational age (1977-1981).

An update of the Swedish reference standards for weight, length, and head circumference at birth, for each week of gestational age, is presented. It is based on the total Swedish cohorts of infants born 1977-1981 (n = 475,588). A "healthy population" (79%) was extracted, using prospectively collected data. Weekly (28-42 weeks) grouped data for length and head circumference were well approximated by the normal distribution, but the distributions for birthweight were positively skewed. The original skewed distributions for birthweight were transformed, using the square root, resulting in distributions close to the Gaussian. For smoothing purposes, the weakly values for the mean and the standard deviation were both fitted by a third degree polynomial function. These functions also make possible the calculation of the continuous variable, standard deviation score, for individual newborn infants as well as a comparison of distributions between groups of infants. The reference values and charts presented here have two major advantages over the current Swedish ones: the sample size used is now sufficiently large at the lower gestational ages, so that empirically found variations can be used, and the skewness of the birth weight distribution has been taken into account. The use of the reference standards presented here improves and facilitates evaluation of size deviation at birth.

Birth Weight↗