Global burden of 288 causes of death and life expectancy decomposition in 204 countries and territories and 811 subnational locations, 1990-2021: a systematic analysis for the Global Burden of Disease Study 2021

BACKGROUND

Regular, detailed reporting on population health by underlying cause of death is fundamental for public health decision making. Cause-specific estimates of mortality and the subsequent effects on life expectancy worldwide are valuable metrics to gauge progress in reducing mortality rates. These estimates are particularly important following large-scale mortality spikes, such as the COVID-19 pandemic. When systematically analysed, mortality rates and life expectancy allow comparisons of the consequences of causes of death globally and over time, providing a nuanced understanding of the effect of these causes on global populations.

METHODS

The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 cause-of-death analysis estimated mortality and years of life lost (YLLs) from 288 causes of death by age-sex-location-year in 204 countries and territories and 811 subnational locations for each year from 1990 until 2021. The analysis used 56 604 data sources, including data from vital registration and verbal autopsy as well as surveys, censuses, surveillance systems, and cancer registries, among others. As with previous GBD rounds, cause-specific death rates for most causes were estimated using the Cause of Death Ensemble model-a modelling tool developed for GBD to assess the out-of-sample predictive validity of different statistical models and covariate permutations and combine those results to produce cause-specific mortality estimates-with alternative strategies adapted to model causes with insufficient data, substantial changes in reporting over the study period, or unusual epidemiology. YLLs were computed as the product of the number of deaths for each cause-age-sex-location-year and the standard life expectancy at each age. As part of the modelling process, uncertainty intervals (UIs) were generated using the 2·5th and 97·5th percentiles from a 1000-draw distribution for each metric. We decomposed life expectancy by cause of death, location, and year to show cause-specific effects on life expectancy from 1990 to 2021. We also used the coefficient of variation and the fraction of population affected by 90% of deaths to highlight concentrations of mortality. Findings are reported in counts and age-standardised rates. Methodological improvements for cause-of-death estimates in GBD 2021 include the expansion of under-5-years age group to include four new age groups, enhanced methods to account for stochastic variation of sparse data, and the inclusion of COVID-19 and other pandemic-related mortality-which includes excess mortality associated with the pandemic, excluding COVID-19, lower respiratory infections, measles, malaria, and pertussis. For this analysis, 199 new country-years of vital registration cause-of-death data, 5 country-years of surveillance data, 21 country-years of verbal autopsy data, and 94 country-years of other data types were added to those used in previous GBD rounds.

FINDINGS

The leading causes of age-standardised deaths globally were the same in 2019 as they were in 1990; in descending order, these were, ischaemic heart disease, stroke, chronic obstructive pulmonary disease, and lower respiratory infections. In 2021, however, COVID-19 replaced stroke as the second-leading age-standardised cause of death, with 94·0 deaths (95% UI 89·2-100·0) per 100 000 population. The COVID-19 pandemic shifted the rankings of the leading five causes, lowering stroke to the third-leading and chronic obstructive pulmonary disease to the fourth-leading position. In 2021, the highest age-standardised death rates from COVID-19 occurred in sub-Saharan Africa (271·0 deaths [250·1-290·7] per 100 000 population) and Latin America and the Caribbean (195·4 deaths [182·1-211·4] per 100 000 population). The lowest age-standardised death rates from COVID-19 were in the high-income super-region (48·1 deaths [47·4-48·8] per 100 000 population) and southeast Asia, east Asia, and Oceania (23·2 deaths [16·3-37·2] per 100 000 population). Globally, life expectancy steadily improved between 1990 and 2019 for 18 of the 22 investigated causes. Decomposition of global and regional life expectancy showed the positive effect that reductions in deaths from enteric infections, lower respiratory infections, stroke, and neonatal deaths, among others have contributed to improved survival over the study period. However, a net reduction of 1·6 years occurred in global life expectancy between 2019 and 2021, primarily due to increased death rates from COVID-19 and other pandemic-related mortality. Life expectancy was highly variable between super-regions over the study period, with southeast Asia, east Asia, and Oceania gaining 8·3 years (6·7-9·9) overall, while having the smallest reduction in life expectancy due to COVID-19 (0·4 years). The largest reduction in life expectancy due to COVID-19 occurred in Latin America and the Caribbean (3·6 years). Additionally, 53 of the 288 causes of death were highly concentrated in locations with less than 50% of the global population as of 2021, and these causes of death became progressively more concentrated since 1990, when only 44 causes showed this pattern. The concentration phenomenon is discussed heuristically with respect to enteric and lower respiratory infections, malaria, HIV/AIDS, neonatal disorders, tuberculosis, and measles.

INTERPRETATION

Long-standing gains in life expectancy and reductions in many of the leading causes of death have been disrupted by the COVID-19 pandemic, the adverse effects of which were spread unevenly among populations. Despite the pandemic, there has been continued progress in combatting several notable causes of death, leading to improved global life expectancy over the study period. Each of the seven GBD super-regions showed an overall improvement from 1990 and 2021, obscuring the negative effect in the years of the pandemic. Additionally, our findings regarding regional variation in causes of death driving increases in life expectancy hold clear policy utility. Analyses of shifting mortality trends reveal that several causes, once widespread globally, are now increasingly concentrated geographically. These changes in mortality concentration, alongside further investigation of changing risks, interventions, and relevant policy, present an important opportunity to deepen our understanding of mortality-reduction strategies. Examining patterns in mortality concentration might reveal areas where successful public health interventions have been implemented. Translating these successes to locations where certain causes of death remain entrenched can inform policies that work to improve life expectancy for people everywhere.

FUNDING

Bill & Melinda Gates Foundation.

Stretching oneself too thin and facing ethical challenges: Healthcare professionals' experiences during the COVID-19 pandemic

BACKGROUNDS

Most countries are facing increased pressure on healthcare resources. A better understanding of how healthcare providers respond to new demands is relevant for future pandemics and other crises.

OBJECTIVES

This study aimed to explore what nurses and doctors in Norway reported as their main ethical challenges during two periods of the COVID-19 pandemic: February 2021 and February 2022.

RESEARCH DESIGN

A longitudinal repeated cross-sectional study was conducted in the Western health region of Norway. The survey included an open-ended question about ethical challenges among doctors and nurses in hospital departments. Free-text comments were analysed using Systematic Text Condensation and also presented in a frequency table.

ETHICAL CONSIDERATIONS

Ethical approval was granted by the Regional Research Ethics Committee in Western Norway (131,421). All participants provided consent when participating in the study.

RESULTS

In 2021, 249 and in 2022, 163 healthcare professionals responded to the open-ended question. Nurses and doctors reported three main categories of ethical challenges related to the COVID-19 pandemic: (1) barriers that hindered them in acting as they ethically would have wanted to do; (2) priority-setting dilemmas linked to overtreatment, transfer of resources and ranking patient needs; and (3) workload expansion threatening work-life balance and employees' health. Category one comprised of resource barriers, regulatory barriers, system barriers, and personal barriers. Regulatory barriers, especially visitor restrictions for next-of-kin, were the most frequently reported in 2021. Resource barriers, related to the increased scarcity of qualified staff, were most frequently reported in 2022. Clinicians stretched themselves thin to avoid compromising on care, diagnostics, or treatment.

CONCLUSIONS

Developing clinicians' ability to handle and cope with limited healthcare resources is necessary. To foster resilience and sustainability, healthcare leaders, in collaboration with their staff, should ensure fair priority-setting and initiate reflections among doctors and nurses on what it implies to provide 'good enough' care.

The associations between different types of infections and circadian preference and shift work

Disturbed sleep and circadian disruption are reported to increase the risk of infections. People with an evening circadian preference and night workers typically report insufficient sleep, and the aims of the present study were to investigate possible associations between various types of infections and circadian preference and shift work status. Data were collected from an online cross-sectional survey of 1023 participants recruited from the Norwegian practice-based research network in general practice - PraksisNett. The participants completed questions about circadian preference (morning type, intermediate type, evening type), work schedule (day work, shift work without nights, shift work with night shifts), and whether they had experienced infections during the last three months (common cold, throat infection, ear infection, sinusitis, pneumonia/bronchitis, COVID-19, influenza-like illness, skin infection, gastrointestinal infection, urinary infection, venereal disease, eye infection). Data were analyzed with chi-square tests and logistic regression analyses with adjustment for relevant confounders (gender, age, marital status, country of birth, children living at home, and educational level). Results showed that evening types more often reported venereal disease compared to morning types (OR = 4.01, confidence interval (CI) = 1.08-14.84). None of the other infections were significantly associated with circadian preference. Shift work including nights was associated with higher odds of influenza-like illness (OR = 1.97, CI = 1.10-3.55), but none of the other infections. In conclusion, neither circadian preference nor shift work seemed to be strongly associated with risk of infections, except for venereal disease (more common in evening types) and influenza-like illness (more common in night workers). Longitudinal studies are needed for causal inferences.

Self-reported short and long sleep duration, sleep debt and insomnia are associated with several types of infections: Results from the Norwegian practice-based research network in general practice - PraksisNett

Objective

The objective was to assess the association between self-reported infections and sleep duration, sleep debt, chronic insomnia, and insomnia severity.

Methods

In total, 1023 participants were recruited from the Norwegian practice-based research network in general practice to a cross-sectional online survey with validated questions about sleep habits and insomnia symptoms (Bergen Insomnia Scale (BIS) and Insomnia Severity Index (ISI)), and whether they had experienced various infections during the last three months. Data were analyzed with chi-square tests and logistic regressions with adjustment for relevant confounders.

Results

Self-reported short sleep duration (<6 h) was significantly associated with increased odds of throat infection (OR = 1.60), ear infection (OR = 2.92), influenzalike illness (OR = 1.81) and gastrointestinal infection (OR = 1.91) whereas long sleep duration (>9 h) was associated with increased odds of throat (OR = 3.33) and ear infections (OR = 5.82), compared to sleep duration of 6-9 h, respectively. Sleep debt of >2 h was associated with increased odds of the common cold (OR = 1.67), throat infection (OR = 2.58), ear infection (OR = 2.84), sinusitis (OR = 2.15), pneumonia/bronchitis (OR = 3.97), influenzalike illness (OR = 2.66), skin infection (OR = 2.15), and gastrointestinal infection (OR = 2.80), compared to no sleep debt. Insomnia (based on BIS and ISI) was associated with throat infection (OR = 2.06, 2.55), ear infection (OR = 2.43, 2.45), sinusitis (OR = 1.82, 1.80), pneumonia/bronchitis (OR = 2.23, 3.59), influenzalike illness (OR = 1.77, 1.90), skin infection (OR = 1.64, 2.06), gastrointestinal infection (OR = 1.94, 3.23), and eye infection (OR = 1.99, 2.95).

Conclusions

These novel findings support the notion that people who have insufficient sleep or sleep problems are at increased risk of infections.

The association between self-reported sleep problems, infection, and antibiotic use in patients in general practice

Objectives

There is emerging evidence that sleep problems and short sleep duration increase the risk of infection. We aimed to assess whether chronic insomnia disorder, chronic sleep problems, sleep duration and circadian preference based on self-report were associated with risk of infections and antibiotic use among patients visiting their general practitioner (GP).

Methods

We conducted a cross-sectional study of 1,848 unselected patients in Norway visiting their GP during 2020.The patients completed a one-page questionnaire while waiting for the consultation, that included the validated Bergen Insomnia Scale (BIS), questions on self-assessed sleep problem, sleep duration and circadian preference and whether they have had any infections or used antibiotics in the last 3 months. Relative risks (RR) were estimated using modified Poisson regression models.

Results

The risk of infection was 27% (95% CI RR 1.11-1.46) and 44% higher (95% CI 1.12-1.84) in patients sleeping < 6 h and >9 h, respectively, compared to those sleeping 7-8 h. The risk was also increased in patients with chronic insomnia disorder or a chronic sleep problem. For antibiotic use, the risk was higher for patients sleeping < 6 h, and for those with chronic insomnia disorder or a chronic sleep problem.

Conclusions

Among patients visiting their GP, short sleep duration, chronic insomnia and chronic sleep problem based on self-report were associated with higher prevalence of infection and antibiotic use. These findings support the notion of a strong association between sleep and infection.

Associations between excessive fatigue and pain, sleep, mental-health and work factors in Norwegian nurses

AIM

To investigate whether pain, sleep duration, insomnia, sleepiness, work-related factors, anxiety, and depression associate with excessive fatigue in nurses.

BACKGROUND

Fatigue among nurses is a problem in the context of ongoing nursing shortages. While myriad factors are associated with fatigue not all relationships are understood. Prior studies have not examined excessive fatigue in the context of pain, sleep, mental health, and work factors in a working population to determine if associations between excessive fatigue and each of these factors remain when adjusting for each other.

METHODS

A cross-sectional questionnaire study among 1,335 Norwegian nurses. The questionnaire included measures for fatigue (Chalder Fatigue Questionnaire, score ≥4 categorized as excessive fatigue), pain, sleep duration, insomnia (Bergen Insomnia Scale), daytime sleepiness (Epworth Sleepiness Scale), anxiety and depression (Hospital Anxiety and Depression Scale), and work-related factors. Associations between the exposure variables and excessive fatigue were analyzed using chi-square tests and logistic regression analyses.

RESULTS

In the fully adjusted model, significant associations were found between excessive fatigue and pain severity scores for arms/wrists/hands (adjusted OR (aOR) = 1.09, CI = 1.02-1.17), hips/legs/knees/feet (aOR = 1.11, CI = 1.05-1.18), and headaches/migraines (aOR = 1.16, CI = 1.07-1.27), sleep duration of <6 hours (aOR = 2.02, CI = 1.08-3.77), and total symptom scores for insomnia (aOR = 1.05, CI = 1.03-1.08), sleepiness (aOR = 1.11, CI = 1.06-1.17), anxiety (aOR = 1.09, CI = 1.03-1.16), and depression (aOR = 1.24, CI = 1.16-1.33). The musculoskeletal complaint-severity index score (aOR = 1.27, CI = 1.13-1.42) was associated with excessive fatigue in a separate model adjusted for all variables and demographics. Excessive fatigue was also associated with shift work disorder (OR = 2.25, CI = 1.76-2.89) in a model adjusted for demographics. We found no associations with shift work, number of night shifts and number of quick returns (<11 hours between shifts) in the fully adjusted model.

CONCLUSION

Excessive fatigue was associated with pain, sleep- and mental health-factors in a fully adjusted model.

Shift workers are at increased risk of severe COVID-19 compared with day workers: Results from the international COVID sleep study (ICOSS) of 7141 workers

The present study had two main aims. First, to investigate whether shift/night workers had a higher prevalence and severity of COVID-19 compared with day workers. Second, to investigate whether people regularly working in face-to-face settings during the pandemic exhibited a higher prevalence and severity of COVID-19 compared with those having no need to be in close contact with others at work. Data consisted of 7141 workers from 15 countries and four continents who participated in the International COVID Sleep Study-II (ICOSS-II) between May and December 2021. The associations between work status and a positive COVID-19 test and several indications of disease severity were tested with chi-square tests and logistic regressions adjusted for relevant confounders. In addition, statistical analyses were conducted for the associations between face-to-face work and COVID-19 status. Results showed that shift/night work was not associated with an increased risk of COVID-19 compared to day work. Still, shift/night workers reported higher odds for moderate to life-threatening COVID-19 (adjusted odds ratio (aOR) = 2.71, 95%-confidence interval = 1.23-5.95) and need for hospital care (aOR = 5.66, 1.89-16.95). Face-to-face work was associated with an increased risk of COVID-19 (aOR = 1.55, 1.12-2.14) but not with higher disease severity. In conclusion, shift/night work was not associated with an increased risk of COVID-19, but when infected, shift/night workers reported more severe disease. Impaired sleep and circadian disruption commonly seen among shift/night workers may be mediating factors. Working face-to-face increased the risk of COVID-19, likely due to increased exposure to the virus. However, face-to-face work was not associated with increased disease severity.

Prevalence of insomnia and hypnotic use in Norwegian patients visiting their general practitioner

BACKGROUND

Sleep problems are common in the general population, but there are few studies on the prevalence of sleep problems and hypnotic use among patients in general practice.

OBJECTIVES

To estimate the prevalence of insomnia (based on the Diagnostic and Statistical Manual of Mental Disorders [DSM], version 5), self-reported sleep problems and hypnotic use among patients in general practice, and explore whether the prevalence depended on patient characteristics.

METHODS

A cross-sectional study with questionnaire data collected by 114 final-year medical students while deployed in different general practices in Norway during 2020. A total of 1,848 consecutive and unselected patients (response rate 85.2%) visiting their general practitioners (GPs) completed a one-page questionnaire, that included the validated Bergen Insomnia Scale (BIS), questions on for how long they have had a sleep problem, hypnotic use, and background characteristics. Associations were estimated using a modified Poisson regression model.

RESULTS

The prevalence of chronic insomnia according to BIS was 48.3%, while 46.9% reported chronic sleep problems (sleep problems of ≥3 months) and 17.8% reported hypnotic use. Females, patients with low compared with higher education, and patients who slept shorter or longer than 7-8 h, had higher risk of chronic insomnia disorder (CID), chronic self-reported sleep problems (CSP), and hypnotic use. The oldest age group (≥65 years) had lower risk of chronic insomnia compared with the youngest (18-34) but twice the probability of hypnotic use.

CONCLUSIONS

CID, CSP, and hypnotic use were prevalent among patients visiting their GP. Insomnia can be effectively treated and deserves more attention among GPs.

A shift to something better? A longitudinal study of work schedule and prescribed sleep medication use in nurses

OBJECTIVES

To explore whether a change in work schedule was associated with a change in the probability of prescribed sleep medication use.

METHODS

A longitudinal study with annual questionnaire data (2008/2009-2021, except 2019) on work schedule (day work only, shift work without nights and shift work with nights) and prescribed sleep medication use from 2028 Norwegian nurses (mean age 31.7 years, 90.5% women at baseline) who participated in the ongoing Survey of Shift work, Sleep and Health (SUSSH). Associations were estimated using a random effects model, and a fixed effects regression model in which nurses were included as their own control to account for potential unobserved confounding.

RESULTS

In both models, day work was associated with a more than 50% lower probability of sleep medication use compared with shift work with nights (adjusted OR (aOR) 0.50, 95% CI 0.27 to 0.93 in the random effects model, and an aOR 0.32, 95% CI 0.14 to 0.70 in the fixed effects regression model). Shift work without nights was associated with a non-statistically significant reduction in sleep medication use within nurses in the fixed effects regression model when compared with shift work with nights (aOR 0.66, 95% CI 0.37 to 1.20).

CONCLUSIONS

Day work was associated with a significant reduced probability of prescribed sleep medication use compared with shift work with nights. This indicates that quitting night work will improve sleep and thereby reduce hypnotic use.

Association of sweetened carbonated beverage consumption during pregnancy and ADHD symptoms in the offspring: a study from the Norwegian Mother, Father and Child Cohort Study (MoBa)

PURPOSE

Intrauterine exposures influence offspring health and development. Here we investigated maternal intake of sweetened carbonated beverages (SCB) during pregnancy and its association with ADHD symptoms in the offspring.

METHODS

This study was based on the Norwegian Mother, Father and Child Cohort Study (MoBa) and the Medical Birth Registry of Norway. Maternal diet mid-pregnancy was assessed using a food frequency questionnaire (FFQ). All mothers who responded to the FFQ and a questionnaire when their child was 8 years of age were included (n = 39,870). The exposure was defined as maternal intake (daily servings) of SCB, using no daily intake as reference. Outcome was offspring ADHD symptoms, evaluated as a continuous standardized ADHD score and as a binary outcome of six or more ADHD symptoms vs. five symptoms or less. Associations were analysed using log-binomial regression and linear mixed regression models with adjustment for covariates.

RESULTS

The adjusted regression coefficients for the standardized ADHD offspring symptom score were 0.31 [95% confidence intervals (0.001, 0.62)] and 0.46 (0.15, 0.77) for maternal daily intake of ≥ 1 glasses of SCB, when the models included adjustments for total energy intake or energy intake from other sources than SCBs and sweet drinks, respectively. The corresponding adjusted relative risks were 1.16 (1.004, 1.34) and 1.21. (1.05, 1.39) for drinking ≥ 1 glasses daily.

CONCLUSION

In a large pregnancy cohort with offspring followed until 8 years of age, we found an association between maternal daily intake of SCB and offspring ADHD symptoms. These results suggest a weak positive relationship between prenatal exposure to SCB and offspring ADHD.

Sleep medication and melatonin use among Norwegian nurses - A cross-sectional study

Aim

To estimate the prevalence of sleep medication and melatonin use among nurses and to assess if factors related to work, sleep or mental health, were associated with such use.

Design

A cross‐sectional study.

Methods

A questionnaire survey including 2,798 Norwegian nurses. Associations were estimated using a modified Poisson regression model.

Results

In total, 7.5%, 4.6% and 2.0% of the nurses included in the present study reported prescribed sleep medication, over‐the‐counter sleep medication or melatonin use in the last year, respectively. Short sleep duration, sleep problems and psychological conditions were strongly associated with both prescribed and over‐the‐counter sleep medication use. Nurses who worked more than 60 night shifts in the last year were at increased risk of sleep medication use.

Maternal Chronic Conditions and Risk of Cerebral Palsy in Offspring: A National Cohort Study

BACKGROUND AND OBJECTIVES

Previous studies suggest that children of mothers with certain chronic conditions may be at increased risk of cerebral palsy (CP). We explored possible associations between 17 maternal chronic conditions and CP in offspring.

METHODS

We conducted a prospective cohort study of Norwegian children born in 1990-2012 and surviving to 2 years of age. Information on maternal chronic conditions during pregnancy were extracted from the Medical Birth Registry of Norway (1990-2012). Information on chronic conditions in mothers and fathers recorded in the Norwegian Patient Registry (2008-2014) was available for a subset of children. CP diagnoses were extracted from the National Insurance Scheme (1990-2014) and the Norwegian Patient Registry (2008-2014). We estimated relative risks (RRs) and 95% confidence intervals (CIs) of CP in offspring of parents with chronic conditions compared with the general population using log binominal regression models.

RESULTS

A total of 1 360 149 Norwegian children, including 3575 children with CP (2.6 per 1000 live births), fulfilled the inclusion criteria. The highest risk of CP was among offspring of mothers with type 2 diabetes (RR 3.2; 95% CI 1.8-5.4), lupus erythematosus (RR 2.7; 95% CI 0.9-8.3), type 1 diabetes (RR 2.2; 95% CI 1.4-3.4), and Crohn disease (RR 2.1; 95% CI 1.0-4.1) during pregnancy. No increased risks were seen for offspring of fathers with chronic conditions.

CONCLUSIONS

Several maternal chronic conditions were associated with increased risk of CP in offspring. Maternal autoimmune disorders carried a particular risk.

Priority-setting dilemmas, moral distress and support experienced by nurses and physicians in the early phase of the COVID-19 pandemic in Norway

Background:

The global COVID-19 pandemic has imposed challenges on healthcare systems and professionals worldwide and introduced a ´maelstrom´ of ethical dilemmas. How ethically demanding situations are handled affects employees’ moral stress and job satisfaction.

Aim:

Describe priority-setting dilemmas, moral distress and support experienced by nurses and physicians across medical specialties in the early phase of the COVID-19 pandemic in Western Norway.

Research design:

A cross-sectional hospital-based survey was conducted from 23 April to 11 May 2020.

Ethical considerations:

Ethical approval granted by the Regional Research Ethics Committee in Western Norway (131421).

Findings:

Among the 1606 respondents, 67% had experienced priority-setting dilemmas the previous two weeks. Healthcare workers who were directly involved in COVID-19 care, were redeployed or worked in psychiatry/addiction medicine experienced it more often. Although 59% of the respondents had seen adverse consequences due to resource scarcity, severe consequences were rare. Moral distress levels were generally low (2.9 on a 0–10 scale), but higher in selected groups (redeployed, managers and working in psychiatry/addiction medicine). Backing from existing collegial and managerial structures and routines, such as discussions with colleagues and receiving updates and information from managers that listened and acted upon feedback, were found more helpful than external support mechanisms. Priority-setting guidelines were also helpful.

Discussion:

By including all medical specialties, nurses and physicians, and various institutions, the study provides information on how the COVID-19 mitigation also influenced those not directly involved in the COVID-19 treatment of patients. In the next stages of the pandemic response, support for healthcare professionals directly involved in outbreak-affected patients, those redeployed or those most impacted by mitigation strategies must be a priority.

Conclusion:

Empirical research of healthcare workers experiences under a pandemic are important to identify groups at risks and useful support mechanisms.

Parental education and the risk of cerebral palsy for children: an evaluation of causality

AIM

To explore whether increasing parental education has a causal effect on risk of cerebral palsy (CP) in the child, or whether unobserved confounding is a more likely explanation.

METHOD

We used data from Norwegian registries on approximately 1.5 million children born between 1967 and 2011. We compared results from a traditional cohort design with results from a family-based matched case-control design, in which children with CP were matched to their first cousins without CP. In addition, we performed a simulation study to assess the role of unobserved confounding.

RESULTS

In the cohort design, the odds of CP were reduced in children of mothers and fathers with higher education (adjusted odds ratio [OR] 0.67, 95% confidence interval [CI] 0.60-0.75 for maternal education, and adjusted OR 0.75, 95% CI 0.67-0.85 for paternal education). In the family-based case-control design, only an association for maternal education remained (adjusted OR 0.80, 95% CI 0.64-0.99). Results from a simulation study suggested that this association could be explained by unobserved confounding.

INTERPRETATION

A causal effect of obtaining higher education on risk of CP in the child is unlikely. Results stress the importance of continued research on the role of genetic and environmental risk factors that vary by parents' educational level.

WHAT THIS PAPER ADDS

Children of higher-educated parents had significantly lower odds of cerebral palsy (CP). There was no evidence of difference in risk of CP within first cousins whose mothers or fathers had different educational levels. Association between parental education and odds of CP did not reflect a causal effect.

Parental socioeconomic status and risk of cerebral palsy in the child: evidence from two Nordic population-based cohorts

Background

We investigated whether the risk of cerebral palsy (CP) in the child varies by parents’ socioeconomic status, in Denmark and Norway.

Methods

We included almost 1.3 million children born in Demark during 1981–2007 and 2.4 million children born in Norway during 1967–2007, registered in the Medical Birth registries. Data on births were linked to Statistics Denmark and Norway to retrieve information on parents’ education and relationship status and, in Denmark, also income. CP diagnoses were obtained from linkage with national registries. We used multivariate log-binominal regression models to estimate relative risk (RR) of CP according to parental socioeconomic status.

Results

There was a strong trend of decreasing risk of CP with additional education of both the mother and the father. These trends were nearly identical for the two parents, with a one-third reduction in risk for those with the highest education compared with parents with the lowest education. When both parents had high education, risk of CP was further reduced (RR 0.58, 0.53–0.63). Women with partners had a reduction in risk (RR 0.79, 0.74–0.85) compared with single mothers overall. Risk patterns were stable over time, across countries and within spastic bilateral and unilateral CP. Household income was not associated with risk of CP.

Conclusions

Risk of CP in two Scandinavian countries was lower among educated parents and mothers with a partner, but unrelated to income. Factors underlying this stable association with education are unknown, but could include differences in potentially modifiable lifestyle factors and health behaviours.

Cerebral palsy among children of immigrants in Denmark and the role of socioeconomic status

BACKGROUND

Children of immigrants in Denmark have excess risk for some of the most well-established risk factors for cerebral palsy (CP).

OBJECTIVES

To study differences in risk of CP between children of immigrants and children of Danish-born mothers, and explore whether socioeconomic status drives any potential association.

METHODS

A register-based cohort study including 1,274,616 children born in Denmark between 1981 and 2007. Of these, 2807 had a validated CP diagnosis in the Danish CP Register. We estimated the risk of CP as odds ratios (OR) using logistic regression and assessed mediation through socioeconomic status using natural effect models.

RESULTS

In children of Danish-born mothers, 2.2/1000 had CP overall and the prevalence was similar for children of immigrants. However, children of immigrants had lower risk of unilateral spastic CP than children of Danish native-born mothers; OR = 0.59 (95% CI:0.38-0.91) for Western and OR = 0.79 (95% CI:0.61-1.03) for Non-Western immigrants. By contrast, the risk of bilateral spastic CP was higher in children of Non-Western immigrants (OR = 1.27 (95% CI:1.05-1.53)), especially from Turkey and Pakistan compared with children of Danish native-born mothers. The mediation analysis revealed an indirect effect (through maternal educational level and household income) with an OR of 1.06 (95% CI:0.99-1.14) for children of Non-Western immigrants.

CONCLUSIONS

While children of immigrants had lower risk of unilateral spastic CP than children of Danish-born mothers, the risk of bilateral spastic CP was increased in children of Non-Western immigrants. Socioeconomic status did not appear to be a significant contributor to the increased risk of bilateral spastic CP.

Maternal Prepregnancy BMI and Risk of Cerebral Palsy in Offspring

OBJECTIVES

To investigate the association between maternal pre-pregnancy BMI and risk of cerebral palsy (CP) in offspring.

METHODS

The study population consisted of 188 788 children in the Mothers and Babies in Norway and Denmark CP study, using data from 2 population-based, prospective birth cohorts: the Norwegian Mother and Child Cohort Study and the Danish National Birth Cohort. Prepregnancy BMI was classified as underweight (BMI <18.5), lower normal weight (BMI 18.5-22.9), upper normal weight (BMI 23.0-24.9), overweight (BMI 25.0-29.9), and obese (BMI ≥30). CP diagnoses were obtained from the national CP registries. Associations between maternal prepregnancy BMI and CP in offspring were investigated by using log-binomial regression models.

RESULTS

The 2 cohorts had 390 eligible cases of CP (2.1 per 1000 live-born children). Compared with mothers in the lower normal weight group, mothers in the upper normal group had a 40% excess risk of having a child with CP (relative risk [RR], 1.35; 95% confidence interval [CI], 1.03-1.78). Excess risk was 60% (RR, 1.56; 95% CI, 1.21-2.01) for overweight mothers and 60% (RR, 1.55; 95% CI 1.11-2.18) for obese mothers. The risk of CP increased ∼4% for each unit increase in BMI (RR, 1.04; 95% CI, 1.02-1.06). Estimates changed little with adjustment for mother's occupational status, age, and smoking habits.

CONCLUSIONS

Higher prepregnancy maternal BMI was associated with increased risk of CP in offspring.

Cohort profile: cerebral palsy in the Norwegian and Danish birth cohorts (MOBAND-CP)

PURPOSE

The purpose of MOthers and BAbies in Norway and Denmark cerebral palsy (MOBAND-CP) was to study CP aetiology in a prospective design.

PARTICIPANTS

MOBAND-CP is a cohort of more than 210 000 children, created as a collaboration between the world's two largest pregnancy cohorts-the Norwegian Mother and Child Cohort study (MoBa) and the Danish National Birth Cohort. MOBAND-CP includes maternal interview/questionnaire data collected during pregnancy and follow-up, plus linked information from national health registries.

FINDINGS TO DATE

Initial harmonisation of data from the 2 cohorts has created 140 variables for children and their mothers. In the MOBAND-CP cohort, 438 children with CP have been identified through record linkage with validated national registries, providing by far the largest such sample with prospectively collected detailed pregnancy data. Several studies investigating various hypotheses regarding CP aetiology are currently on-going.

FUTURE PLANS

Additional data can be harmonised as necessary to meet requirements of new projects. Biological specimens collected during pregnancy and at delivery are potentially available for assay, as are results from assays conducted on these specimens for other projects. The study size allows consideration of CP subtypes, which is rare in aetiological studies of CP. In addition, MOBAND-CP provides a platform within the context of a merged birth cohort of exceptional size that could, after appropriate permissions have been sought, be used for cohort and case-cohort studies of other relatively rare health conditions of infants and children.