Falling asleep: the determinants of sleep latency.

BACKGROUND: Difficulty falling asleep (prolonged sleep latency) is a frequently reported problem in school-aged children. AIMS: This study aimed to describe the distribution of sleep latency and factors that influence its duration. METHODS: 871 children of European mothers were recruited at birth. 591 (67.9%) children took part in the follow-up at 7 years of age. Sleep and daytime activity were measured objectively by an actigraph worn for 24 h. RESULTS: Complete sleep data were available for 519 children (87.8%) with a mean age of 7.3 years (SD 0.2). Median sleep latency was 26 minutes (interquartile range 13-42). Higher mean daytime activity counts were associated with a decrease in sleep latency (-1.2 minutes per 102 movement count per minute, p = 0.05). Time spent in sedentary activity was associated with an increase in sleep latency (3.1 minutes per hour of sedentary activity, p = 0.01). CONCLUSIONS: These findings emphasise the importance of physical activity for children, not only for fitness, cardiovascular health and weight control, but also for promoting good sleep.

Risk factors for asthma at 3.5 and 7 years of age.

BACKGROUND: It has been suggested that factors in early life including exposure to allergens and microbes may influence the development of asthma. OBJECTIVE: To identify risk factors for asthma in early childhood. Methods Eight-hundred and seventy-one children of European mothers were enrolled at birth, of whom 385 (44.2%) were born small for gestational age (SGA) and 486 were appropriate for gestational age (AGA). Data were collected at birth, 12 months, 3.5 years of age (y) and 7 y. The outcome of interest (current wheeze) was defined as a positive response to the question: 'Has your child had wheezing or whistling in the chest in the last 12 months?' RESULTS: Participation rate was 85.4% at 1 y, 63.1% at 3.5 y and 68.0% at 7 y. The prevalence of asthma was 23.8% at 3.5 y and 18.1% at 7 y. Antibiotic use in the first year of life and day care in the first year of life were associated with increased risk of wheeze at 7 y [odds ratio (OR)=4.3 95% confidence interval (CI) (1.8-10.1) and OR=2.8 95% CI (1.2-6.5), respectively], but not at 3.5 y. Exposure to dogs was a risk factor for asthma at both ages [OR=2.1 95% CI (1.1-3.8)] as was sleeping on a used cot mattress in the first year of life [OR=1.8 95% CI (1.0-3.2)]. CONCLUSIONS: There was a significant association between antibiotic use and day care in the first year of life and wheezing at 7 y but not at 3.5 y. This strengthens the argument that these factors increase the risk of asthma. We have also made the novel observation that sleeping on a used mattress in the first year of life is a risk factor for wheezing at 3.5 and 7 y. Capsule summary This prospective study of 871 children made the novel observation that sleeping on a used mattress in the first year of life was a risk factor for wheezing at 3.5 and 7 y.

On the Breslow-Holubkov estimator.

Breslow and Holubkov (J Roy Stat Soc B 59:447-461 1997a) developed semiparametric maximum likelihood estimation for two-phase studies with a case-control first phase under a logistic regression model and noted that, apart for the overall intercept term, it was the same as the semiparametric estimator for two-phase studies with a prospective first phase developed in Scott and Wild (Biometrica 84:57-71 1997). In this paper we extend the Breslow-Holubkov result to general binary regression models and show that it has a very simple relationship with its prospective first-phase counterpart. We also explore why the design of the first phase only affects the intercept of a logistic model, simplify the calculation of standard errors, establish the semiparametric efficiency of the Breslow-Holubkov estimator and derive its asymptotic distribution in the general case.

Family-specific approaches to the analysis of case-control family data.

Case-control studies augmented by the values of responses and covariates from family members allow investigators to study the association between the response and genetics and environment by relating differences in the response directly to within-family differences in covariates. However, existing approaches for case-control family data parameterize covariate effects in terms of the marginal probability of response, the same effects that one estimates from standard case-control studies. This article focuses on the estimation of family-specific covariate effects and develops efficient methods to fit family-specific models such as binary mixed-effects models. We also extend the approach to cover any setting where one has a fully specified model for the vector of responses in a family. We illustrate our approach using data from a case-control family study of brain cancer and consider the use of weighted and conditional likelihood methods as alternatives.

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.

Maternal stress, social support and preschool children's intelligence.

BACKGROUND: Despite some research suggesting maternal stress may be associated with cognitive impairment in preschool children, there has been little direct investigation of the association between maternal stress, social support and children's intelligence. AIM: To determine whether maternal stress and social support during pregnancy and during the child's early years of life are associated with the intelligence test performance of preschool children. STUDY DESIGN: Five hundred and fifty European mothers and children enrolled in the Auckland Birthweight Collaborative Study at birth were interviewed when the child was 3 1/2 years of age. SUBJECTS: All children were full term gestation and approximately half the sample were small for gestational age at birth (SGA = birthweight < or = 10th percentile). OUTCOME MEASURE: The cognitive ability of children aged 3 1/2 years was assessed using the Stanford Binet Intelligence Scale 4th Edition. RESULTS: In the total sample, maternal stress and lack of social support during pregnancy were significantly associated with lower intelligence test scores of children. In the group of SGA children, maternal stress post pregnancy was significantly associated with lower intelligence test scores in children. There is evidence that for some children the presence of good social support for mothers may reduce the negative effects of maternal stress on children's cognitive development. CONCLUSION: Maternal stress and lack of social support appear to be associated with lower intelligence test scores of preschool children. Social support may attenuate some of the negative effects of maternal stress on intelligence in children born small for gestational age.

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. OBJECTIVES: To examine factors associated with a diagnosis of AD at 3.5 years of age, especially those factors implicated by the hygiene hypothesis. METHODS: The Auckland Birthweight Collaborative study is a case-control study of risk factors for small for gestational age babies. Cases were born at term with birthweight < or = 10th centile; controls were appropriate for gestational age, with birthweight > 10th centile. The infants were assessed at birth, 1 year and 3.5 years of age. Data were collected by parental interview and examination of the child. AD was defined as the presence of an itchy rash in the past 12 months with three or more of the following: history of flexural involvement; history of generally dry skin; history of atopic disease in parents or siblings; and visible flexural dermatitis as per photographic protocol. Statistical analyses took into account the disproportionate sampling of the study population. RESULTS: Analysis was restricted to European subjects. Eight hundred and seventy-one children were enrolled at birth, 744 (85.4%) participated at 1 year, and 550 (63.2%) at 3.5 years. AD was diagnosed in 87 (15.8%) children seen at 3.5 years. The prevalence of AD did not differ by birthweight. AD at 3.5 years was associated with raised serum IgE > 200 kU L(-1), and wheezing, asthma, rash or eczema at 1 year. In multivariate analysis, adjusted for parental atopy and breastfeeding, AD at 3.5 years was associated with atopic disease in the parents: maternal atopy only, adjusted odds ratio (OR) 3.83, 95% confidence interval (CI) 1.20-12.23; paternal atopy only, adjusted OR 3.59, 95% CI 1.09-11.75; both parents atopic, adjusted OR 6.12, 95% CI 2.02-18.50. There was a higher risk of AD with longer duration of breastfeeding: < 6 months, adjusted OR 6.13, 95% CI 1.45-25.86; > or = 6 months, adjusted OR 9.70, 95% CI 2.47-38.15 compared with never breastfed. These findings remained significant after adjusting for environmental factors and a personal history of atopy. AD at 3.5 years was associated with owning a cat at 3.5 years (adjusted OR 0.45, 95% CI 0.21-0.97) but not with owning a dog at 3.5 years, pets at 1 year, nor with older siblings. Furthermore, AD at 3.5 years was not associated with gender, socioeconomic status, maternal smoking, parity, damp, mould, immunizations, body mass index or antibiotic use in first year of life. CONCLUSIONS: A personal and a parental history of atopic disease are risk factors for AD at 3.5 years. Duration of breastfeeding was associated with an increased risk of AD. No association was found with those factors implicated by the hygiene hypothesis. This study suggests that breastfeeding should not be recommended for the prevention of AD.

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.

Stress and lack of social support as risk factors for small-for-gestational-age birth.

AIM: To determine the contributions of social support and perceived stress to the risk of small-for-gestational-age birth. METHODS: The investigation was a case-control study of mothers of infants born at 37 or more completed weeks of gestation. Cases weighed less than the sex-specific 10th percentile for gestational age at birth (small for gestational age (SGA), n = 836), and controls (appropriate for gestational age (AGA), n = 870) comprised a random selection of heavier babies. RESULTS: In univariate analyses measures of informal social support, but not perceived stress or formal social support, were associated with SGA birth. It was found that Asian mothers are less likely to receive support from families and friends. After adjustment for ethnicity, informal social support was not associated with SGA. CONCLUSIONS: Support appears to reduce the risk of SGA births, but after adjustment for ethnicity this is no longer the case. Stress during pregnancy was not associated with SGA birth.

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. CONCLUSIONS: Maternal smoking in pregnancy is a major risk factor for SGA. This study suggests that mothers should be advised to cease smoking completely during pregnancy, and that a reduction in the number of cigarettes smoked or smoking low tar or nicotine concentration cigarettes does not reduce the risk of SGA.

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. METHODOLOGY: All babies were born at 37 or more completed weeks of gestation in one of three hospitals in Auckland. Cases weighed less than the sex specific 10th percentile for gestational age at birth, and controls (appropriate-for-gestational-age (AGA)) were a random selection of heavier babies. Information was collected by maternal interview and from obstetric databases. RESULTS: Information from 1714 completed interviews (844 SGA and 870 AGA) was available for analysis. Computerized obstetric records were available for 1691 of the 1701 women who consented to such access. In a multivariate analysis allowing for sex, gestational age at birth, social class and other potential confounders, mothers who smoked had a significantly increased risk of an SGA baby (adjusted OR 2.41; 95% CI 1.78-3.28), as did primiparous mothers (adjusted OR 1.34; 95% CI 1.03-1.73), mothers of Indian ethnicity (adjusted OR 3.22; 95% CI 1.95-5.30), women with pre-eclamptic toxaemia (adjusted OR 2.42; 95% CI 1.08-5.40) and those with pre-existing hypertension toxaemia (adjusted OR 5.49; 95% CI 1.81-16.71). Mothers of SGA infants were shorter (P < 0.001) and reported lower prepregnancy body weights (P < 0.001) than mothers of AGA infants. The population attributable fraction for smoking suggests that up to 18% of SGA infants born in the ABC Study could be related to maternal smoking. CONCLUSIONS: Risk factors associated with SGA births in other countries are also important in New Zealand. Smoking in pregnancy is an important and potentially modifiable behaviour, and efforts to decrease the number of women who smoke during pregnancy should be encouraged.

Smoking during pregnancy: how reliable are maternal self reports in New Zealand?

OBJECTIVE: To determine the reliability of self reports of smoking during pregnancy. METHODS: Residual sera from early and late antenatal blood samples were tested for cotinine for all pregnancies over a six month period. Over an overlapping 12 month period, a postal questionnaire on smoking was also sent to all new mothers (n = 4857) when their baby was 4-8 weeks old. Smoking status from obstetric booking notes was also obtained. RESULTS: The cotinine-validated smoking prevalence was 31.3% for the first trimester and 27.7% for the third trimester. Questionnaire self reported prevalences were 19.2% and 15.7% for the first and third trimesters respectively, and 18.9% for obstetric booking. Of cotinine-validated smokers, 22% denied smoking-self deceivers. Of mothers who replied to the questionnaire, a half appeared to systematically under report the amount they smoked. CONCLUSIONS: Nearly a quarter of smoking pregnant women did not report smoking. Moreover, of those who did, the amount smoked was often under reported. This tendency to under report may rise as pressures to stop smoking increase. Accurate measures of smoking prevalence in pregnant women will require objective testing.

Breastfeeding in Canterbury over three decades.

AIM: To document breastfeeding levels in Canterbury between 1968 to 1994. METHODS: The method of feeding at discharge from hospital, at 4 weeks and at 3 months of age was obtained from maternal obstetric records, Plunket nursing notes, parent interviews or by self completed questionnaires. Data were compiled for the years 1968 to 1994. RESULTS: In 1968, only half of all mothers were breastfeeding when discharged. However, rates have steadily increased since then so that by 1990, 90% of infants were recorded as being breastfed at discharge. Levels of exclusive breastfeeding have also increased. By 1992-4, 82.2% of babies were being exclusively breastfed at discharge from hospital, 72.4% at 4 weeks and 62.5% at 3 months. CONCLUSION: Levels of breastfeeding in Canterbury are now relatively high. The Public Health Commission has set a target for 75% of infants to be fully breastfed at 3 months of age by the year 2000. To achieve this the circumstances that hinder breastfeeding need to be addressed.

Prevalence of smoking in early pregnancy by census area: measured by anonymous cotinine testing of residual antenatal blood samples.

AIM: To accurately measure the prevalence of smoking in early pregnancy by census area units (CAU) in Christchurch. METHODS: Smoking status in pregnancy was determined by serum cotinine assay for all antenatal blood samples taken over a 6 month period. CAUs in Christchurch were grouped into quartiles according to the proportion of maternal smokers. Social factors from 1991 census data were used to describe the characteristics of each quartile. RESULTS: The overall rate of smoking in pregnancy was 33.0%. Rates ranged from 10.6% to 56.9% for the census area groups. CAUs in the upper quartile (39-57% of women smoking in pregnancy) were clustered together geographically and were associated with lower socioeconomic indices. The strongest correlation was between average income with smoking rates (Pearson correlation coefficient 0.76). CONCLUSION: Smoking rates in pregnancy have remained at around 30% for at least 20 years, with some areas of the city having rates nearly double this. It would seem logical to promote smoke-free pregnancy activities in localities with the highest rates of smoking. Future evaluation of the efficacy of such programmes should be done using objective measurements.

The length of the referral chain after failing preschool tympanometry.

AIMS: To describe the time intervals during the process of detection and management of chronic secretory otitis media/glue ear. METHOD: Tympanometry records of 508 preschool children who failed both tympanometry screening and the subsequent retest were examined. Additional information was obtained from 205 parents/caregivers by telephone interview. RESULTS: Calculations of time intervals between tympanometry screening and retesting showed that 75% of children had been retested within 20 weeks and 95% by 40 weeks. Two-thirds (67%) of children had visited their general practitioner within 4 weeks of failing their retest, although 13% had still yet to be seen by 20 weeks. The mean time interval between the initial general practitioner visit and subsequently being seen by an ENT specialist was 20 weeks in the public system compared to 5 weeks if seen privately (p < 0.001). CONCLUSION: The preschool tympanometry screening programme functioned well, although there were delays in retesting 25% of preschoolers. There were substantial time intervals for some children for each link in the referral chain. The reasons for these delays needs investigation to determine how much it is a part of the treatment process and how much due to waiting list problems.

Women in low income groups smoke more: Canterbury 1976-92.

AIM: To examine the relationship between income and levels of smoking in women of child-bearing age. METHODS: Census area units within the Christchurch region were divided into five groups according to average income for each of the census years 1976, 1981 and 1991 respectively. Smoking rates were obtained from census data for 1976 and 1981. For 1992, data from a questionnaire on smoking during pregnancy and obstetric records were used. RESULTS: For all years, higher proportions of women from low income groups smoked. The overall percentage of female smokers in Canterbury fell slightly from 31.6% in 1976 to 27.5% in 1981. There were 27.1% of pregnant women smoking in 1992. There were marked changes by economic groups. The percentage of smokers in the highest income group fell from 24.8% in 1976 to 21.0% in 1981: an 18% fall. Smokers in the lowest income group increased from 36.8% in 1976 to 39.8% in 1981. The same patterns were seen for smoking in pregnancy in the 1992 data. CONCLUSION: While the downward trend for smokers in the high income groups is good news, it is of concern that the proportion of smokers in the lower income groups remains so high. Young women have the highest rates of smoking, which is of special concern when they become pregnant. Smokefree intervention programmes need to be specifically targeted at these groups.

Infant feeding patterns in Canterbury.

AIM: To examine infant feeding patterns during the first 6 months of life in Canterbury. METHODS: A random sample of 10% of all births over a 12 month period in Canterbury was taken from birth notifications (n = 520). Information on the type of feeding was recorded prospectively at three time periods and extracted from available Plunket nursing notes. The participation rate was 81%. Data from nonparticipants on the method of feeding at discharge was obtained from obstetric records. RESULTS: Overall, 90.7% were breastfed at discharge. There was no difference between breastfeeding rates of the participants (91%) compared to the nonparticipants. For participants, 88% were exclusively breastfed at discharge which steadily declined to 36% at 24 weeks. However, some breastmilk was still being given to 70% at 24 weeks. CONCLUSION: Breastfeeding rates are good in comparison to other nations. However, there is room for improvement particularly maintaining exclusive breastfeeding to at least four months. This could be stimulated by the Baby Friendly Hospital Initiative and the fostering of a baby friendly environment to further support and promote breastfeeding in the community.

Microalbuminuria in a middle-aged workforce. Effect of hyperglycemia and ethnicity.

OBJECTIVE: To determine the prevalence of microalbuminuria in a mixed, ethnic population and to find the extent that ethnic variation in microalbuminuria can be explained by abnormal glucose metabolism, obesity, hypertension, hypertriglyceridemia, and life-style factors. RESEARCH DESIGN AND METHODS: Urinary albumin concentrations were measured in 5467 middle-aged Maori, Pacific Islander, and European workers who participated in a health-screening survey of 46 New Zealand companies. Participants provided a first-voided, morning urine sample; had a 75-g oral glucose tolerance test; had weight, height, and blood pressure measured; and completed a self-administered questionnaire about past medical history and sociodemographic status. RESULTS: A significantly higher prevalence of microalbuminuria was found in individuals with new cases of diabetes mellitus (24.1%), in cases of diabetes mellitus previously diagnosed (20.6%), and in those with impaired glucose tolerance (16.1%) compared with nondiabetic individuals (4.0%). Moreover, in the general population, a piecewise linear relationship was detected between albuminuria and plasma glucose with significant changes of slope corresponding with 2 h plasma glucose concentrations (95% confidence interval) of 6.7 (6.4-7.0) and 9.2 (8.6-9.8) mM, respectively. After adjusting for sex, obesity, hypertension, hypertriglyceridemia, cigarette smoking, and heavy alcohol consumption in a multivariate model, glycemia was the most significant determinant of urinary albumin concentrations in all three ethnic groups. However, blood glucose concentrations did not completely explain the higher relative risk (95% confidence interval) of microalbuminuria in Maori (5.97; 4.48-7.78) and Pacific Islander (5.33; 4.13-6.87) workers compared with European workers. CONCLUSIONS: Of the variables investigated, hyperglycemia was the most important factor explaining the high prevalence of microalbuminuria in Maori and Pacific Islander workers compared with the European workers. However, only 14.9% of the variation in urinary albumin concentrations was found in our multivariate model, and we have speculated on the contribution of other factors such as diet and coexisting renal diseases.

Dietary nutrient intakes and slight albuminuria in people at least 40 years old.

We studied the relation between diet and slight albuminuria in 5416 people, ages 40 years and over, who participated in a health screening survey of a local workforce. Degree of albuminuria showed log-linear univariate relations with dietary protein, cholesterol, and sodium intakes, and negative log-linear univariate relations with dietary fiber and polyunsaturated to saturated fat (P/S) ratio. After adjusting for age, gender, and ethnicity, the relative risk (95% confidence interval) for slight albuminuria was significantly increased in people reporting dietary cholesterol consumption > 226 mg/day compared with people reporting consumption < or = 226 mg/day [1.32 (1.02, 1.70)], and significantly reduced in people reporting dietary fiber consumption > 26 g/day compared with people reporting consumption < or = 26 g/day [0.74 (0.58, 0.95)]. There was no significant effect of dietary protein, P/S ratio, or salt intake. We conclude that risk of slight albuminuria is increased by consumption of dietary cholesterol and reduced by consumption of dietary fiber.