Table 1.
Sample characteristics in the Gemini twin study (n 2336) and National Diet and Nutrition Survey (NDNS) (n 386) (Mean values and standard deviations; numbers and percentages)
| Gemini | NDNS | |||
|---|---|---|---|---|
| Characteristics | Mean | sd | Mean | sd |
| Age at diet diary completion (months) | 20·6 | 1·1 | 26·4 | 8·8 |
| Weight at birth (kg) | 2·5 | 0·5 | – | |
| Weight SDS at birth* | −0·5 | 0·9 | – | |
| Gestational age (weeks) | 36·2 | 2·5 | – | |
| n | % | n | % | |
| Feeding method 0–3 months† | ||||
| Breast-fed infants (%) | 1468 | 62·8 | – | |
| Bottle-fed infants | 868 | 37·2 | – | |
| Sex | ||||
| Boys | 1157 | 49·5 | 207 | 53·6 |
| Girls | 1179 | 50·5 | 179 | 46·4 |
| Ethnicity | ||||
| White | 2222 | 95·1 | 328 | 85·0 |
| Non-white | 106 | 4·9 | 58 | 15·0 |
| Socio-economic status‡ | ||||
| High | 1056 | 46 | 158 | 40·9 |
| Intermediate | 370 | 16·1 | 79 | 20·5 |
| Low | 872 | 37·9 | 149 | 38·6 |
Weight SDS references children’s weights against the population mean (weight SDS=0) in 1990( 11 ), for the child’s age at measurement, sex and gestational age. A weight SDS>0 indicates higher weight, and a weight SDS<0 indicates lower weight compared with children of the same age, sex and gestational age.
The proportion of infants breast-fed in the first 3 months from birth was obtained with the question ‘which feeding method did you use in the first 3 months?’ with response options ranging from 1=entirely breast-feeding to 6=entirely bottle feeding. Categories 1–5 were classified as ‘breast-fed’ and category 6 as ‘bottle-fed’.
Classified using the Office for National Statistics( 10 ) and grouped into higher (higher and lower managerial and professional occupations), intermediate (intermediate occupations, small employers and own account workers) and lower socio-economic status (lower supervisory and technical occupations, (semi)routine occupations, never worked and long-term unemployed).