Camilla Schmidt Morgen

Socioeconomic position and the risk of preterm birth : a study within the Danish National Birth Cohort

BACKGROUND Low socioeconomic position is generally associated with increased risk of preterm birth, but it remains unclear whether the inequality depends on the socioeconomic measure used, if the associations differ according to the degree of prematurity, and how individual level risk factors mediate the association. METHODS The hazard ratios (HR) of preterm birth associated with five different measures of socioeconomic position and three degrees of preterm birth were analysed in a dataset of 75 890 singleton pregnancies (1996-2002) from the Danish National Birth Cohort. This, and the mediating role of selected individual level risk factors (smoking, alcohol consumption, binge drinking, pre-pregnancy body mass index, gestational weight gain) were estimated, using Cox regression analyses. RESULTS Mothers with <10 years of education had an elevated risk of preterm birth compared with mothers with >12 years of education and the association interacted with parity, while income and occupation affected the risk to a lesser degree. The adjusted HR for less educated nulliparous and parous women were 1.22 (95% CI 1.04-1.42) and 1.56 (95% CI 1.31-1.87), respectively, compared with women with >12 years of education. For parous women with <10 years of education inclusion of smoking in the model decreased the HR of preterm birth to 1.43 (95% CI 1.19-1.72). CONCLUSIONS Maternal educational level was the strongest predictor of preterm birth among five socioeconomic measures and the gradient did not differ significantly according to the degree of preterm birth. For parous women smoking explained some of the educational gradient but in general the selected risk factors only reduced the relative educational gradient in preterm birth marginally.

Socio-economic inequality in preterm birth: a comparative study of the Nordic countries from 1981 to 2000

During the 1980s and 1990s, there were large social and structural changes within the Nordic countries. Here we examine time changes in risks of preterm birth by maternal educational attainment in Denmark, Finland, Norway and Sweden. Information on gestational age and maternal socio-economic position was obtained from the NorCHASE database, which includes comparable population-based register data of births from Denmark, Finland, Sweden and Norway from 1981 to 2000. The risks of very preterm birth (<32 gestational weeks) and moderately preterm birth (32-36 gestational weeks) were calculated by maternal educational attainment and analysed in 5-year intervals from 1981 to 2000. Compared with mothers with >12 years of education, mothers with <10 years of education had similarly increased risks of very, and to a lesser extent moderately, preterm birth in all four countries. The educational gradient increased slightly over time in very preterm births in Denmark, while there was a slight narrowing of the gap in Sweden. In moderately preterm births, the educational inequality gap was constant over the study period in Denmark, Norway and Sweden, but narrowed in Finland. The educational gradient in preterm birth remained broadly stable from 1981 to 2000 in all four countries. Consequently, the socio-economic inequalities in preterm birth were not strongly influenced by structural changes during the period.

Trends in Prevalence of Overweight and Obesity in Danish Infants, Children and Adolescents – Are We Still on a Plateau?

Background After the worldwide steep increase in child and adolescent overweight and obesity during the last decades, there is now evidence of a levelling off in the prevalence in many countries in the Western world. Aim To examine whether there still is a plateau in the prevalence of overweight and obesity in Danish children and adolescents, or whether the prevalence is decreasing or rising again. Methods The trends in the prevalence rates were based on three data sets providing comparable repeated estimates: 1) the Danish Health Visitors Child Health Database (DHVCHD) with measurements on infant and childhood height and weight from 2002 to 2011 (n up to 39,984), 2) the Danish National Birth Cohort (DNBC) with maternal reports of measured infant and childhood height and weight from 1998 to 2010 (n up to 56,826) and 3) the Danish part of the Health Behaviour in School-aged Children survey (HBSC) with self-reported information on adolescent height and weight from the years 2002 to 2010 (n = 16,557). Overweight and obesity were categorized according to WHO growth standards. Trends were assessed by repeated point estimates and linear regression analyses providing regression coefficients for changes in per cent per year with 95% confidence intervals (CI). Results The prevalence rates of overweight and obesity for infants, children and adolescents showed a mixed pattern of decline, stability and increase (ranging from -1.10 through 0.29 per cent per year with CI’s from -3.10 through 2.37). Overall, there were no consistent statistically significant trends upwards or downwards, although some significant downward trends in childhood and adolescence were observed. Conclusion This study, based on data from 1998 through 2011, showed that the prevalence rates of overweight and obesity among Danish infants, children and adolescents were largely still on a plateau with tendencies for a decline among children and adolescents.

Obesity: global trends in the prevalence of overweight and obesity.

A new report provides compelling evidence of the high prevalence of overweight and obesity throughout the world. The prevalence has increased since 1980, but at different rates across ages, times and locations. Studies exploring the causes of these differences could aid development of effective prevention strategies.

Parental socioeconomic position and development of overweight in adolescence: longitudinal study of Danish adolescents.

BackgroundAn inverse social gradient in overweight among adolescents has been shown in developed countries, but few studies have examined whether weight gain and the development of overweight differs among adolescents from different socioeconomic groups in a longitudinal study. The objective was to identify the possible association between parental socioeconomic position, weight change and the risk of developing overweight among adolescents between the ages 15 to 21.MethodsProspective cohort study conducted in Denmark with baseline examination in 1996 and follow-up questionnaire in 2003 with a mean follow-up time of 6.4 years. A sample of 1,656 adolescents participated in both baseline (mean age 14.8) and follow-up (mean age 21.3). Of these, 1,402 had a body mass index (BMI = weight/height2kg/m2) corresponding to a value below 25 at baseline when adjusted for age and gender according to guidelines from International Obesity Taskforce, and were at risk of developing overweight during the study period. The exposure was parental occupational status. The main outcome measures were change in BMI and development of overweight (from BMI < 25 to BMI > = 25).ResultsAverage BMI increased from 21.3 to 22.7 for girls and from 20.6 to 23.6 in boys during follow-up. An inverse social gradient in overweight was seen for girls at baseline and follow-up and for boys at follow-up. In the full population there was a tendency to an inverse social gradient in the overall increase in BMI for girls, but not for boys. A total of 13.4% developed overweight during the follow-up period. Girls of lower parental socioeconomic position had a higher risk of developing overweight (ORs between 4.72; CI 1.31 to 17.04 and 2.03; CI 1.10-3.74) when compared to girls of high parental socioeconomic position. A tendency for an inverse social gradient in the development of overweight for boys was seen, but it did not meet the significance criteriaConclusionsThe levels of overweight and obesity among adolescents are high and continue to rise. Results from this study suggest that the inverse social gradient in overweight becomes steeper for girls and emerges for boys in late adolescence (age span 15 to 21 years). Late adolescence seems to be an important window of opportunity in reducing the social inequality in overweight among Danish adolescents.

Association between smoking and the risk of heavy drinking among young women: a prospective study

AIM To address the association between smoking habits and the risk of later heavy drinking among young women. METHODS Repeated assessments of alcohol and smoking habits were obtained in 1991-93 and 1999-2000 in a Danish representative cohort in Copenhagen. A total of 6369 non- to moderate-drinking Danish women, aged 20-29 years at baseline, attended a follow-up examination and were included in the study. The risk of becoming a heavy drinker (more than 14 drinks per week) 8 years after enrolment was analyzed by means of logistic regression. RESULTS A total of 177 women became heavy drinkers during follow-up. Daily smoking at baseline was associated with an increased risk of becoming a heavy drinker 8 years later. Relative to nonsmokers, the adjusted odds ratios (OR) for becoming a heavy drinker associated with smoking 1-14, 15-24, or more than 24 cigarettes per day were 1.6 (95% confidence intervals (CI) 1.1-2.4), 1.7 (CI 1.1-2.6), and 2.3 (CI 0.9-5.9), respectively. Age at sexual debut modified the effect of smoking, and women with a debut before the age of 15 years had an adjusted OR of 2.9 (CI 1.1-3.9) compared to never-smokers while there seemed to be no effect among women with a sexual debut after the age of 18. In addition, relative to nondrinkers, all of the moderate (1-5 units per week), medium (6-10 units), and large (10-14 units) alcohol consumption at baseline were associated independently with becoming a heavy drinker 8 years later. CONCLUSIONS This study suggests that smoking is an important predictor of later heavy drinking among young women and that this relatively elevated risk is most pronounced among women with an early sexual debut.

Socioeconomic position and the risk of spontaneous abortion: a study within the Danish National Birth Cohort

Objectives To investigate the relationship between different indicators of socioeconomic position and the risk of spontaneous abortion. Design Cohort study. Setting 1996–2002, Denmark. Participants All first time participants, a total of 89 829 pregnant women, enrolled in the Danish National Birth Cohort were included in the present study. Overall, 4062 pregnancies ended in spontaneous abortion. Information on education, income and labour market attachment in the year before pregnancy was drawn from national registers. Main outcome measure Spontaneous abortion, that is, fetal death within the first 22 weeks of pregnancy, was the outcome of interest. The authors estimated HRs of spontaneous abortion using Cox regression analysis with gestational age as the underlying time scale. Results Women with <10 years of education had an elevated risk of spontaneous abortion when compared with women with >12 years of education (HR 1.19 (95% CI 1.05 to 1.34)). The HR estimates for the four lowest income quintiles were all increased (HRs between 1.09 and 1.15) as compared with the upper quintile but did not differ considerably from each other. In general, no statistically significant association was found between labour market attachment and the risk of spontaneous abortion; however, the group of women on disability pension had an increased HR of spontaneous abortion when compared with women who were employed (HR 1.32 (95% CI 0.82 to 2.13)). Conclusions Educational level and income were inversely associated with the risk of spontaneous abortion. As these factors most likely are non-causally related to spontaneous abortion, the findings indicate that factors related to social position, probably of the environmental and behavioural type, may affect spontaneous abortion risk. The study highlights the need for studies addressing such exposures in order to prevent spontaneous abortions.

Socioeconomic disparities in birth weight and body mass index during infancy through age 7 years: a study within the Danish National Birth Cohort

Background Socioeconomic inequalities in birth weight and in body mass index (BMI) later in childhood are in opposite directions, which raises questions about when during childhood the change in direction happens. We examined how maternal and paternal education and household income were associated with birthweight z-scores and with BMI z-scores at age 5 and 12 months and 7 years, and we examined the socioeconomic differences in the tracking of these z-scores across infancy and childhood. Methods The associations were studied in a cohort of children in the Danish National Birth Cohort, single born between 1997 and 2003, for whom information on body size from at least 1 of 4 time points (n=85 062) was recorded. We examined the associations using linear mixed-effects modelling. Results Children from families with a low maternal and paternal educational level changed their body size z-scores upwards between birth and age 7 years. At age 5 and 12 months, there were no educational gradient. A low maternal educational level was associated with lower birth weight for gestational age z-scores at birth for boys (−0.199; 95% CI −0.230 to −0.169) and girls (−0.198; 95% CI −0.229 to −0.167) and higher BMI z-scores at age 7 for boys (0.198; 95% CI 0.154 to 0.242) and girls (0.218; 95% CI 0.173 to 0.264). There was not a similarly clear pattern in the tracking between different household income groups. However, a low household income level was associated with higher z-scores of both birth weight and BMI at age 7 years, but with a much weaker gradient at 5 and 12 months. Conclusions The educational gradient shifts from positive with birth weight, to none during infancy to inverse with BMI at age 7 years. In contrast, the income gradient was positive at birth and at 7 years and much weaker during infancy.

Prenatal risk factors influencing childhood BMI and overweight independent of birth weight and infancy BMI: a path analysis within the Danish National Birth Cohort

Background and objectives:Prenatal risk factors for childhood overweight may operate indirectly through development in body size in early life and/or directly independent hereof. We quantified the effects of maternal and paternal body mass index (BMI), maternal age, socioeconomic position (SEP), parity, gestational weight gain, maternal smoking during pregnancy, caesarean section, birth weight, and BMI at 5 and 12 months on BMI and overweight at 7 and 11 years.Methods:Family triads with information on maternal, paternal and child BMI at ages 7 (n=29 374) and 11 years (n=18 044) were selected from the Danish National Birth Cohort. Information originated from maternal interviews and medical health examinations. Path analysis was used to estimate the direct and indirect effects of prenatal risk factors on childhood BMI z-scores (BMIz per unit score of the risk factor). Logistic regression was used to examine associations with overweight.Results:The strongest direct effects on BMIz at age 7 were found for maternal and paternal BMI (0.19 BMIz and 0.14 BMIz per parental BMIz), low SEP (0.08 BMIz), maternal smoking (0.12 BMIz) and higher BMIz at 5 and 12 months (up to 0.19 BMIz per infant BMIz). For BMIz at age 11 with BMIz at age 7 included in the model, similar effects were found, but the direct effects of BMIz at age 5 and 12 months were mediated through BMI at age 7 (0.62 BMIz per BMIz). Same results were found for overweight. The sum of the direct effects can be translated to approximate absolute measures: 2.4 kg at 7 years, 5.7 kg at 11 years, in a child with average height and BMI.Conclusions:Parental BMI, low SEP and smoking during pregnancy have persisting, strong and direct effects on child BMI and overweight independent of birth weight and infancy BMI.

Maternal smoking during pregnancy and offspring overweight: is there a dose–response relationship? An individual patient data meta-analysis

Background/objectivesA number of meta-analyses suggest an association between any maternal smoking in pregnancy and offspring overweight obesity. Whether there is a dose–response relationship across number of cigarettes and whether this differs by sex remains unclear.Subject/methodsStudies reporting number of cigarettes smoked during pregnancy and offspring BMI published up to May 2015 were searched. An individual patient data meta-analysis of association between the number of cigarettes smoked during pregnancy and offspring overweight (defined according to the International Obesity Task Force reference) was computed using a generalized additive mixed model with non-linear effects and adjustment for confounders (maternal weight status, breastfeeding, and maternal education) and stratification for sex.ResultsOf 26 identified studies, 16 authors provided data on a total of 238,340 mother–child-pairs. A linear positive association was observed between the number of cigarettes smoked and offspring overweight for up to 15 cigarettes per day with an OR increase per cigarette of 1.03, 95% CI = [1.02–1.03]. The OR flattened with higher cigarette use. Associations were similar in males and females. Sensitivity analyses supported these results.ConclusionsA linear dose–response relationship of maternal smoking was observed in the range of 1–15 cigarettes per day equally in boys and girls with no further risk increase for doses above 15 cigarettes.