and storage iron concentrations in life and between blood ferritin and liver iron concentrations after death.'0 It is reasonable to suppose that if infants who die of SIDS are born with excess tissue iron stores then this would be reflected in the blood ferritin measured soon after birth.The availability of blood spots on stored Guthrie cards enabled us to compare blood ferritin concentrations in the first week of life from victims ofSIDS and controls. A significant difference might have formed the basis of a useful screening test for infants at risk.Plasma ferritin concentrations in normal adults vary from 15 to 300 gg/l and reflect the variable concentrations ofstorage iron present.6There is a similar variability of ferritin concentrations in newborn infants so that wide variations in the mean value of the four control cards for each case are to be expected. The mean value of 93 gg/l in eight samples of cord blood is within the expected range.6 In the cord blood samples the plasma component accounts for a mean of 7% of the total blood ferritin-a smaller proportion than the mean of approximately 20% for adult blood.'0Preliminary studies showed that little ferritin could be extracted from the dried spots of blood on Guthrie cards stored for more than six months. However, with the extraction procedure described above, studies of blood spots stored at temperatures from 4 to 56°C indicated that a recovery of about 25% might be expected for cards stored for prolonged periods of time at room temperature.Our study is limited by the small numbers and because it would not be possible to detect a difference between a case and the control cards of less than 20%. Nevertheless

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Details of room temperature, clothing, and bedding used by night and by day and in winter and in summer were recorded for 649 babies aged 8 to 26 weeks. Room temperature at night was significantly related to outside temperature and duration of heating. Total insulation was significantly related to outside temperature and to minimum room temperature, but there was wide variation in insulation at the same room temperature. High levels of insulation for a given room temperature were found particularly at night and in winter, and were associated with the use of thick or doubled duvets and with swaddling. At least half the babies threw off some or all of their bedding at night, and at least a quarter sweated. Younger mothers and mothers in the lower social groups put more bedclothes over their babies, and the latter also kept their rooms warmer. Many mothers kept their babies warmer during infections.There has recently been interest in the thermal environment of sleeping babies, arising mainly from suggestions that some cases of sudden infant death syndrome (SIDS)'" and haemorrhagic shock and encephalopathy syndrome (HSES)5 may be linked with overheating. A difficulty in evaluating this hypothesis has been the lack of control data. There have been four published surveys, from Exeter,6 Nottingham,7 Leicester,8 and Dunedin (New Zealand),9 of how mothers keep their babies warm.We present the findings of a population survey of the thermal environment of 649 sleeping babies by day and night in summer and in winter. weeks (n=238), or 26 weeks old (n=207). The interviewer recorded full details of clothing and bedding used for the baby's sleep the previous night and for sleep on the day of the visit, inspecting all items to check their type and material. She also recorded the social background of the family, the gestation and birth weight of the baby, the type and duration of heating, the ventilation of the room, whether the baby sweated while sleeping, and what adjustments the mother made if the baby had an infection.The ambient temperature of the baby's sleeping place was measured, for day by a recording at the time of the visit, for night by a maximumminimum thermometer left near the cot and collected next morning (temperature recordings were not available for three babies). Outside temperatures for the same times were obtained from the Meteorological Office. The study continued through all months of the year except August. The data were analysed separately for the 326 mothers who were interviewed in summer and the 323 who were interviewed in winter, summer being defined as the period of British summer time. and were approached for interview. Of these 329 (33-6%) declined to participate or were not available. The social class distribution (by father's occupa-

The purpose of the study was to investigate whether the thermal environment in which babies slept before developing haemorrhagic shock encephalopathy syndrome (HSES) diVered from that of other babies. Data were collected by standardised interview from parents of 31 babies who had had HSES before the age of 7 months and compared with equivalent data for 124 control babies, with matching for outside temperature on the relevant night and for age. Multivariate analysis showed a strong association between HSES and covering of the baby's head by bedding, the odds ratio being 30.7 (95% confidence interval, 2.5 to 384). There were weaker associations with other aspects of the thermal environment. This suggests a link between HSES and some cases of cot death, supports the suggestion that HSES may be caused by overheating, and reinforces advice that babies should be placed to sleep in such a way that they are less likely to become totally covered. (Arch Dis Child 1999;81:155-158)