In an original study of postnatal developmental physiology we used serial antenatal ultrasound scanning to identify fetal growth restriction.6
Any baby with a fetal abdominal girth two or more standard deviations below the mean or who by birth weight was below the second centile at term was deemed to be IUGR. During this initial study, all infants were weighed regularly and deep body temperature monitored at regular intervals, until there were no longer any changes in deep body temperature with sleep.
Now that those IUGR children are about 9 years old, they were recalled for a new study of their cardiovascular status. For comparison we chose controls from a large database of healthy children, who had shown normal fetal growth, were delivered at term and had normal birth weight, and who had been studied previously within the same developmental physiology project. The children in the control group were age matched with the IUGR children. All children had their height and weight measured; the height by a portable Harpenden stadiometer to the nearest millimetre and the weight by a Marsden Professional Physician Scale to the nearest 100 g. The heights of the mothers were also measured similarly. Paternal heights were mostly self‐reported. As part of the normal health surveillance scheme for under‐fives, weights and heights of the children were measured at intervals and recorded in the “Red Book” or parent held record.
For the purpose of the cardiovascular study each child had a full medical examination, and 24‐h recording of ECG and ambulatory blood pressure. This is a report of the changes in body weight and height; cardiovascular changes will be reported elsewhere.
Collation of data
Information including medical conditions, medications taken, birth and perinatal data, heights of parents, and heights and weights of children at different ages was extracted onto a spreadsheet for analysis.
Analysis of weight and height data
We used the commercially available United Kingdom Growth Standards Data Analysis software (LMS Research Disc, Harlow Healthcare, Tyne and Wear, UK) to convert all the weight, height and body mass index (BMI) measurements into age and sex corrected corresponding standard deviation (z) scores with reference to 1990 British growth reference charts.
The z score is a statistical measure of the distance (measured in standard deviations) from the mean of a dataset in a gaussian population. A z score of 0 is at the mean of the population and a z score of +1 or –1 means that the value is 1 SD above or below the mean, respectively. z Score values between +2 and –2 cover 95% of the values in a gaussian population. By using z scores we have standardised our data by reference to the 1990 population mean. Changes of weight z scores were calculated between birth and final weight.
We carried out the statistical analysis using SAS version 9.1.3 for Windows. To determine whether the difference in z scores between the two groups was significant at the various ages of measurement, multivariable general linear models were applied to the data. These models are an extension of multiple linear regression models, in which there is a continuous dependent variable, and a combination of continuous and categorical independent variables, the aim being to quantify the relationship between the predictors and the dependent variable, and to find the best predictors. Potential candidate predictors were: IUGR; duration of breast feeding; whether breast fed or not; maternal height; estimated paternal height; mean parental height; current smoking status in household; maternal smoking status in pregnancy; Indices of Multiple Deprivations (IMD 2004); sex; presence of a major medical problem; and current use of medication.
IMD 2004 is a measure of multiple deprivation at the small area level defined as Lower Layer of Super Output Area (SOA), which was developed from the 2001 census to improve reporting of statistical data. The lower layer of SOA, on which IMD 2004 is based, typically represents an area with a minimum population of 1000 and mean population of 1500, and is more reflective of local population than a much larger electoral ward. The IMD 2004 contains seven domains of deprivation: income; employment; health and disability; education and training; barriers to housing; living environment; and crime.
What is already known on this topic
- Fetal growth restriction can influence subsequent body size.
- There is conflicting evidence that intrauterine growth restriction leads to obesity in later life.
What this study adds
- Children with fetal growth restriction gain weight at a much faster rate but do not fully catch up by the age of 9 years with normal children.
- There is no evidence that fetal growth restriction is associated with later obesity.
Univariable analyses were used to narrow the selection process by eliminating variables with a probability >0.1 of predicting each dependent variable, and then the remaining variables were entered into a multivariable main effects model using a backward stepwise procedure. Significant interactions were then explored. We used this method owing to the small number of subjects per candidate predictor variable.