J. M. D. Thompson

Four modifiable and other major risk factors for cot death: the New Zealand study.

Abstract New Zealands high mortality rate from sudden infant death syndrome (SIDS) prompted the development of the New Zealand Cot Death Study. A report of the analysis of the data from the first year has been published. This report now gives the major identified risk factors from the full 3 year data set. In this case‐control study there were 485 infants who died from SIDS in the post‐neonatal age group, and 1800 control infants, who were a representative sample of all hospital births in the study region. Obstetric records were examined and parental interviews were completed in 97.5% and 86.9% of subjects, respectively. As expected many risk factors for SIDS were confirmed including: lower socio‐economic status, unmarried mother, young mother, younger school‐leaving age of mother, younger age of mother at first pregnancy, late attendance at antenatal clinic, non‐attendance at antenatal classes, Maori, greater number of previous pregnancies, the further south the domicile, winter, low birthweight, short gestation, male infant and admission to a special care baby unit. In addition, however, we identified four risk factors that are potentially amenable to modification. These were the prone sleeping position of the baby (odds ratio (OR) = 3.70; 95% confidence interval (Cl) = 2.91, 4.70); bed sharing (OR = 2.70; 95% Cl = 2.02, 3.62); maternal smoking of 1–9 cigarettes per day (OR = 3.47; 95% Cl = 2.50, 4.83), 10–19 cigarettes per day (OR = 3.94; 95% Cl = 2.87, 5.41) or more than 20 cigarettes per day (OR = 5.90; 95% Cl = 4.20, 8.31); and not breast feeding (OR = 2.39; 95% Cl = 1.88, 3.04). After controlling for all of the above variables, the relative risks associated with prone sleeping position (OR = 4.84). sharing bed (OR = 2.02), maternal smoking (OR = 1.79) and not breast feeding (OR = 1.89) were still statistically significant. Population‐attributable risk calculations suggest that these four risk factors may account for 82% of deaths from SIDS. The SIDS mortality rate may fall to less than 0.7/1000 live births if all parents stop putting their infants down to sleep in the prone position, do not sleep with their baby, do not smoke, and breast feed their infants.

Risk factors for atopic dermatitis in New Zealand children at 3·5 years of age

Background  The prevalence of atopic dermatitis (AD) is increasing in Western societies. The hygiene hypothesis proposes that this is due to reduced exposure to environmental allergens and infections during early life.

Risk factors for small-for-gestational-age babies: The Auckland Birthweight Collaborative Study.

Objective: This case‐control study determined whether internationally recognized risk factors for small‐for‐gestational‐age (SGA) term babies were applicable in New Zealand.

Placenta weight percentile curves for singleton deliveries

Objective  To produce population‐based, gender‐ and gestational‐age‐specific centile curves for placental weight.

Infant room-sharing and prone sleep position in sudden infant death syndrome

BACKGROUND There is evidence that the risk of sudden infant death syndrome is lower among ethnic groups in which parents generally share a room with the infant for sleeping. We investigated whether the presence of other family members in the infants sleeping room affects the risk of the sudden infant death syndrome. METHODS The case-control study covered a region with 78% of all births in New Zealand during 1987-90. Home interviews were completed with parents of 393 (81.0% of total) babies who died from the sudden infant death syndrome aged 28 days to 1 year and 1592 (88.4% of total) controls, selected from all hospital births in the study region. FINDINGS The relative risk of sudden infant death for sharing the room with one or more adults compared with not sharing was 0.19 (95% CI 0.08-0.45) for sharing at night during the last 2 weeks and 0.27 (0.17-0.41) for sharing in the last sleep, after control for other confounders. Sharing the room with one or more children did not affect the relative risk (1.25 [0.86-1.82] for sharing during last 2 weeks; 1.29 [0.85-1.94] for sharing in last sleep). There was a significant interaction (p = 0.033) between not sharing the room with an adult and prone sleep position in the last sleep. Compared with infants sharing the room with an adult and not prone, the multivariate relative risk was 16.99 (10.43-27.69) for infants not sharing with an adult and prone, 3.28 (2.06-5.23) for infants sharing the room and prone, and 2.60 (1.58-4.30) for infants not sharing the room and not prone. The interaction between adult room-sharing and prone sleep position suggests that both exposures may affect the risk of sudden infant death syndrome through a common mechanism. INTERPRETATION We recommend that infants sleep in the same bedroom as their parents at night to reduce the risk of sudden infant death syndrome.

Maternal nutritional risk factors for small for gestational age babies in a developed country: a case-control study

Aims: To assess the effect of maternal diet during pregnancy on the risk of delivering a baby who is small for gestational age (SGA). Methods: Case-control study of 844 cases (SGA) and 870 controls (appropriate size for gestational age (AGA)). Only term (37+ completed weeks of gestation) infants were included. Retrospective food frequency questionnaires were completed at birth on the diet at the time of conception and in the last month of pregnancy. Results: At the time of conception, mothers of AGA infants ate significantly more servings of carbohydrate rich food and fruit, and were more likely to have taken folate and vitamin supplements than mothers of SGA infants. There was some evidence that mothers of AGA infants also ate more servings of dairy products, meat, and fish (0.05 < p < 0.1). However, after adjustment for maternal ethnicity, smoking, height, weight, hypertension, and occupation, fish intake (p  =  0.04), carbohydrate-rich foods (p  =  0.04), and folate supplementation (p  =  0.02) were associated with a reduced risk of SGA. In the last month of pregnancy, only iron supplementation was associated with a reduced risk of SGA (p  =  0.05) after adjustment for potential confounders. Conclusions: This study suggests that small variations in maternal diets within the normal range during pregnancy in developed countries are associated with differences in birth weight.

Smoking, nicotine and tar and risk of small for gestational age babies

Aims: To assess the effect of maternal smoking and environmental tobacco smoke (ETS) on risk of small for gestational age infants (SGA). Methods: Case‐control study of 844 cases and 870 controls. Results: Maternal smoking in pregnancy was associated with an increased risk of SGA (adjusted odds ratio (OR) = 2.41; 95% confidence interval (CI) = 1.78, 3.28). We could not detect an increased risk of SGA with paternal smoking, or with other household smokers when the mother was a non‐smoker, but did find an increased risk with exposure to ETS in the workplace or while socializing. Infants of mothers who ceased smoking during pregnancy were not at increased risk of SGA, but those who decreased but did not stop remained at risk of SGA. There was no evidence that the concentration of nicotine and tar in the cigarettes influenced the risk of SGA.

Breastfeeding and intelligence of preschool children

AIM To investigate whether breastfeeding during infancy is a determinant of intelligence at 3.5 y. METHODS Five hundred and fifty European children enrolled at birth in the Auckland Birthweight Collaborative Study were assessed at 3.5 y of age. Approximately half were small for gestational age (SGA < or =10th percentile) at birth and half were appropriate for gestational age (AGA >10th percentile). Duration of breastfeeding was recorded at maternal interview, and the intelligence of children was assessed using the Stanford Binet Intelligence Scale. Regression analysis was used to calculate estimates of difference in intelligence scores between breastfeeding groups for the total sample and the group of SGA children. Analyses of the total sample were weighted to account for the disproportionate sampling of SGA children. RESULTS Breastfeeding was not significantly related to intelligence scores in the total sample despite a trend for longer periods of breastfeeding to be associated with higher intelligence scores. However, in the SGA group, breastfeeding was significantly related to IQ at 3.5 y. Small for gestational age children who were breastfed for longer than 12 mo had adjusted scores 6.0 points higher than those who were not breastfed (p=0.06). CONCLUSION Breastfeeding may be particularly important for the cognitive development of preschool children born small for gestational age.

Socioeconomic status and preterm birth: New Zealand trends, 1980 to 1999

Background: While a number of countries have reported rising preterm birth rates over the past two decades, none has examined the effects of socioeconomic status on preterm birth at a national level. Aim: To document the changing incidence of preterm birth in New Zealand over the past 20 years and to determine whether particular socioeconomic or ethnic subsections of the population have contributed disproportionately to the changes seen. Methods: Birth registration data routinely available from the New Zealand Health Information Service were analysed for the period 1980–99. Information for a total of 1 079 478 singleton live births was linked by Domicile Code to the New Zealand Deprivation Index, a small area index of deprivation. Results: Singleton preterm birth rates rose by 37.2% during the 20 year period, from 4.3% in 1980 to 5.9% in 1999. Rates increased by 71.9% among those living in the most affluent areas, but by only 3.5% among those living in the most deprived areas, resulting in the disappearance of a socioeconomic gradient in preterm birth that had existed during the early 1980s. Conclusions: This study challenges traditional thinking on the associations between socioeconomic status and preterm birth. Further research is necessary if the changes that have occurred in New Zealand over the past 20 years are to be fully understood.

Parental reported apnoea, admissions to hospital and sudden infant death syndrome

Three studies were undertaken: (i) a nation‐wide case‐control study for sudden infant death syndrome (SIDS), with 393 cases and 1592 controls, examined the association between parental reported apnoea and SIDS; (ii) a case‐cohort study, with 84 cases of parental reported apnoea and 1502 controls, aimed to identify risk factors for apnoea; and (ii) national hospital admission data for ALTE and national SIDS mortality data were compared for the years 1986 to 1994. Parental reported apnoea was associated with a significant increased risk of SIDS [adjusted odds ratio (OR) 1.86; 95% confidence interval (CI) 1.12, 3.09]. The population attributable risk was 8%. There was a significant increased risk for parental reported apnoea in infants who did not die after adjustment for potential confounders with maternal smokers, short gestation and admission to the neonatal unit. There was no association with prone sleeping position, co‐sleeping and bottle feeding. The mean annual admission rate for ALTE was 9.4/1000 live births. This did not change significantly over the study period (1986–1994). In contrast, the SIDS mortality rate decreased from over 4/ 1000 to 2.1/1000. Admission rates were higher for Maori infants and boys.