Sources of heterogeneity in the meta-analysis of observational studies: the example of SIDS and sleeping position

Synthesis methods used to combine observational studies and randomised trials in published meta-analyses

BACKGROUND

This study examined the synthesis methods used in meta-analyses pooling data from observational studies (OSs) and randomised controlled trials (RCTs) from various medical disciplines.

METHODS

We searched Medline via PubMed to identify reports of systematic reviews of interventions, including and pooling data from RCTs and OSs published in 110 high-impact factor general and specialised journals between 2015 and 2019. Screening and data extraction were performed in duplicate. To describe the synthesis methods used in the meta-analyses, we considered the first meta-analysis presented in each article.

RESULTS

Overall, 132 reports were identified with a median number of included studies of 14 [9-26]. The median number of OSs was 6.5 [3-12] and that of RCTs was 3 [1-6]. The effect estimates recorded from OSs (i.e., adjusted or unadjusted) were not specified in 82% (n = 108) of the meta-analyses. An inverse-variance common-effect model was used in 2% (n = 3) of the meta-analyses, a random-effects model was used in 55% (n = 73), and both models were used in 40% (n = 53). A Poisson regression model was used in 1 meta-analysis, and 2 meta-analyses did not report the model they used. The mean total weight of OSs in the studied meta-analyses was 57.3% (standard deviation, ± 30.3%). Only 44 (33%) meta-analyses reported results stratified by study design. Of them, the results between OSs and RCTs had a consistent direction of effect in 70% (n = 31). Study design was explored as a potential source of heterogeneity in 79% of the meta-analyses, and confounding factors were investigated in only 10% (n = 13). Publication bias was assessed in 70% (n = 92) of the meta-analyses. Tau-square was reported in 32 meta-analyses with a median of 0.07 [0-0.30].

CONCLUSION

The inclusion of OSs in a meta-analysis on interventions could provide useful information. However, considerations of several methodological and conceptual aspects of OSs, that are required to avoid misleading findings, were often absent or insufficiently reported in our sample.

Cutaneous adverse events in patients treated with PD-1/PD-L1 checkpoint inhibitors and their association with survival: a systematic review and meta-analysis

Immune-related cutaneous adverse events (irCAEs) in patients treated with programmed cell death-1/programmed death-ligand 1 (PD-1/PD-L1) checkpoint inhibitors may be associated with better clinical outcomes. However, the extent to which these results can be extrapolated to all tumour types remains unclear. Herein, we conducted a meta-analysis of patients with cancer receiving anti-PD-1/PD-L1 immunotherapy, to determine the cumulative incidence of irCAEs and their association with survival. We systematically searched six databases (PubMed, Embase, Cochrane, CNKI, CSPD, and CQVIP database) for all cohort studies reporting the relationship between irCAEs and patient survival from the time of database construction to 1 November, 2020. The primary outcomes were objective response rate (ORR), progression-free survival (PFS), and overall survival (OS), with complete remission (CR), partial remission (PR), stable disease (SD), and progressive disease (PD) as secondary outcomes. Patients with irCAEs exhibited higher ORR, and were more likely to report CR and PR and less likely to develop PD than those who did not experience irCAEs. Moreover, the occurrence of irCAEs was significantly associated with both favourable PFS and OS. Therefore, patients with irCAEs have better survival benefit and a significantly lower risk of tumour progression or death. Hence, the occurrence of irCAEs may be a useful marker for predicting the clinical efficacy of anti-PD-1/PD-L1 immunotherapy.

Safety of Provocative Testing With Intracoronary Acetylcholine and Implications for Standard Protocols

BACKGROUND

Heterogeneity in diagnostic criteria and provocation protocols has posed challenges in understanding the safety of coronary provocation testing with intracoronary acetylcholine (ACh) for the contemporary diagnosis of epicardial and microvascular spasm.

OBJECTIVES

We examined the safety of testing and subgroup differences in procedural risks based on ethnicity, diagnostic criteria, and provocation protocols.

METHODS

PubMed and Embase were searched in November 2021 to identify original articles reporting procedural complications associated with intracoronary ACh administration. The primary outcome was the pooled estimate of the incidence of major complications including death, myocardial infarction, ventricular tachycardia/fibrillation, and shock.

RESULTS

A total of 16 studies with 12,585 patients were included in the meta-analysis. The overall pooled estimate of the incidence of major complications was 0.5% (95% CI: 0.0%-1.3%) without any reports of death. Exploratory subgroup analyses revealed that the pooled incidence of major complications was significantly higher in the studies that followed the contemporary diagnosis criteria for epicardial spasm defined as ≥90% diameter reduction (1.0%; 95% CI: 0.3%-2.0%) but significantly lower in Western populations (0.0%; 95% CI: 0.0%-0.45%). The rate of positive epicardial spasm and the incidence of major complications were similar between provocation protocols using the maximum ACh doses of 100 μg and 200 μg.

CONCLUSIONS

Intracoronary ACh administration for the contemporary diagnosis of epicardial and microvascular spasm is a safe procedure. Moreover, excellent safety records are observed in Western populations primarily presenting with myocardial ischemia and/or infarction with nonobstructive coronary arteries. This study will help standardize ACh testing to improve clinical diagnosis and ensure procedural safety.

The prevalence of chronic pain in young adults: a systematic review and meta-analysis

ABSTRACT

Prior systematic reviews have summarized the prevalence and impact of chronic pain in "average" pediatric (i.e., school-age) and adult (i.e., middle-age) age groups. To our knowledge, this is the first study to describe the prevalence of chronic pain in the subgroup of individuals that fall in between established boundaries of "childhood" and "adulthood" - known as young adulthood. The goal of this research was to meta-analyze prevalence data on pain in young adults based on available data published between 2008 and 2020. Searches were identified with MEDLINE, Embase, and PsycINFO. We included general population and university-based studies presenting prevalence estimates of chronic pain (pain lasting ≥3 months) in young adults. We identified 43 articles providing prevalence estimates across a combined population of 97,437 young adult respondents (age range: 15-34), with studies undertaken in 22 countries. Available data allowed for stratification of prevalence according to pain condition. The overall pooled random-effect prevalence rate of chronic pain in young adults was 11.6%, suggesting that 1 in every 9 young adults experience chronic pain worldwide. Prevalence rates varied considerably according to pain condition. Estimates did not vary according to sex, geographic location, and several study methodological characteristics (i.e., population type, sampling area, sampling year, investigation period, assessment method). Overall, young adult chronic pain is common and should be recognized as a major public health concern. Considering the difficulties young adults face accessing adult healthcare, greater attention is needed to develop transition programs and evidence-based treatments tailored to the unique needs of this age group.

Single nucleotide polymorphisms and the risk of developing a second primary cancer among head and neck cancer patients: a systematic literature review and meta-analysis

BACKGROUND

Head and Neck Cancer (HNC) survivors are at increased risk of developing a second primary cancer (SPC). Along with the environmental risk factors, genetic factors have been associated with a potential increased susceptibility to SPC development. We aim to identify the Single Nucleotide Polymorphisms (SNPs) that contribute to SPC development among HNC survivors through a systematic review and meta-analysis.

METHODS

We searched PubMed, Scopus and ISI Web of Science for eligible studies published in English until January 31st, 2020. We included studies reporting primary data that evaluated the association between SNPs and SPC risk in HNC patients. Data were pooled in a random-effect meta-analyses, when at least two studies on the same SNP evaluated the same genotype model. Heterogeneity was assessed using the χ2-based Q-statistics and the I2 statistics. Quality of the included studies was assessed using the Q-Genie tool.

RESULTS

Twenty-one studies, of moderate to good quality, were included in the systematic review. Fifty-one genes were reported across the included studies to have significant associations with an increased SPC risk. Overall, 81 out of 122 investigated SNPs were significantly associated with the SPC risk. Seven studies were included in the meta-analysis, which showed five SNPs associated with an increased risk of SPC: p21C70T, CT + TT (HR = 1.76; 95% CI: 1.28-2.43); FASLG -844C > T, CT + TT (HR = 1.82; 95% CI: 1.35-2.46), P21 C98A, CA + AA (HR = 1.75; 95% CI: 1.28-2.38); FAS -670A > G (HR = 1.84; 95% CI: 1.28-2.66) and GST-M1, Null genotype (HR = 1.54; 95% CI: 1.13-2.10).

CONCLUSIONS

The identified SNPs in our systematic review and meta-analysis might serve as potential markers for identification of patients at high risk of developing SPC after primary HNC.

PROSPERO REGISTRATION NUMBER

CRD42019135612 .

A systematic review of the quality of reporting of interventions in the surgical treatment of Crohn's anal fistula: an assessment using the TIDiER and Blencowe frameworks

BACKGROUND

Crohn's anal fistula is a challenging condition, and may require multiple surgical procedures. To replicate successful procedures, these must be adequately reported in the literature. The aim of this study was to review the quality of reporting of components of surgical interventions for Crohn's anal fistula.

METHODS

A systematic review was conducted. It was registered with PROSPERO (CRD:42019135157). The Medline and EMBASE databases were searched for studies reporting interventions intended to close fistula in patients with Crohn's disease, published between 1999 and August 2019. Abstracts and full texts were screened for inclusion by two reviewers. Dual extraction of data was performed to compare reporting to the TIDiER and Blencowe frameworks for reporting of interventions.

RESULTS

Initial searches identified 207 unique studies; 38 full texts were screened for inclusion and 33 were included. The most common study design was retrospective cohort (17/33), and the most frequently reported interventions were anal fistula plug (n = 8) and fibrin glue (n = 6). No studies showed coverage of all domains of TIDieR. Reporting was poor among domains related to who provided an intervention, where it was provided, and how it was tailored. Reporting of domains in the Blencowe framework was poor; the majority of studies did not report the component steps of procedures or efforts to standardise them.

CONCLUSIONS

This study demonstrates that reporting on technical aspects of interventions for Crohn's anal fistula is poor. Surgeons should aim to improve reporting to allow accurate reproduction of techniques both in clinical practice and in clinical trials.

Cardiovascular risk factors and mortality in hospitalized patients with COVID-19: systematic review and meta-analysis of 45 studies and 18,300 patients

BACKGROUND

A high prevalence of cardiovascular risk factors including age, male sex, hypertension, diabetes, and tobacco use, has been reported in patients with Coronavirus disease 2019 (COVID-19) who experienced adverse outcome. The aim of this study was to investigate the relationship between cardiovascular risk factors and in-hospital mortality in patients with COVID-19.

METHODS

MEDLINE, Cochrane, Web of Sciences, and SCOPUS were searched for retrospective or prospective observational studies reporting data on cardiovascular risk factors and in-hospital mortality in patients with COVID-19. Univariable and multivariable age-adjusted analyses were conducted to evaluate the association between cardiovascular risk factors and the occurrence of in-hospital death.

RESULTS

The analysis included 45 studies enrolling 18,300 patients. The pooled estimate of in-hospital mortality was 12% (95% CI 9-15%). The univariable meta-regression analysis showed a significant association between age (coefficient: 1.06; 95% CI 1.04-1.09; p < 0.001), diabetes (coefficient: 1.04; 95% CI 1.02-1.07; p < 0.001) and hypertension (coefficient: 1.01; 95% CI 1.01-1.03; p = 0.013) with in-hospital death. Male sex and smoking did not significantly affect mortality. At multivariable age-adjusted meta-regression analysis, diabetes was significantly associated with in-hospital mortality (coefficient: 1.02; 95% CI 1.01-1.05; p = 0.043); conversely, hypertension was no longer significant after adjustment for age (coefficient: 1.00; 95% CI 0.99-1.01; p = 0.820). A significant association between age and in-hospital mortality was confirmed in all multivariable models.

CONCLUSIONS

This meta-analysis suggests that older age and diabetes are associated with higher risk of in-hospital mortality in patients infected by SARS-CoV-2. Conversely, male sex, hypertension, and smoking did not independently correlate with fatal outcome.

Occurrence of metachronous second primary cancer in head and neck cancer survivors: A systematic review and meta-analysis of the literature

OBJECTIVE

Head and neck cancer (HNC) is the sixth leading cancer worldwide with approximately 600,000 new cases per year. Several studies suggest that HNC survivors may have an increased risk of developing second primary cancers (SPCs). A systematic review and meta-analysis was performed aiming to quantify the overall and site-specific risk of metachronous SPCs in HNC survivors.

METHODS

PubMed, Web of Science and Scopus were searched to identify studies published until October 2019. Studies investigating the standardised incidence ratio (SIR) of metachronous SPC were included. A random-effects meta-analysis was performed to calculate the overall and site-specific SIRs. Newcastle-Ottawa Scale was used to assess the study's quality. Heterogeneity was quantified using the I² statistics and explored using meta-regression.

RESULTS

Twenty-six studies were included in the systematic review. Studies differed by the definition of metachronous SPC used. For the meta-analyses, the studies were grouped according to these definitions. In the three groups, the overall risk of metachronous SPC was increased. The highest SPC risk was for oropharynx, oesophagus and lung.

CONCLUSIONS

Head and neck cancer survivors are at increased overall risk of metachronous SPCs. The canonical upper aerodigestive sites, HNLE (head and neck, oesophagus and lung), were the SPC sites with the highest risk.

IMPLICATION FOR CANCER SURVIVORS

Our results emphasise the importance of targeted surveillance strategies aimed at early detection and tertiary preventive interventions.

History of premenstrual syndrome and development of postpartum depression: A systematic review and meta-analysis

BACKGROUND

Premenstrual syndrome (PMS) is thought to be a risk factor for postpartum depression (PPD), but results from studies examining the association have been mixed.

OBJECTIVES

To estimate the association between pre-pregnancy history of PMS and development of PPD and evaluate the risk of bias of included evidence.

SEARCH STRATEGY

PubMed, EMBASE, CINAHL, PsycINFO, Cochrane Library, CNKI, Wanfang Data, and reference lists of relevant papers were searched.

SELECTION CRITERIA

Observational studies that collected pre-pregnancy history of PMS and measured PPD status between one week and one year after delivery were included.

DATA COLLECTION AND ANALYSIS

This study followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Random-effect models were used to calculate pooled odds ratios (ORs) with 95% confidence interval (CI). Small study effect was analysed by funnel plot. Risk of bias was assessed using the Risk of Bias Instrument for Non-Randomized Studies of Exposures (ROBINS-E).

MAIN RESULTS

Our meta-analysis included 19 studies. Overall, women with a pre-pregnancy history of PMS had more than double the odds of PPD compared to those without PMS (OR: 2.20, 95% CI: 1.81-2.68). However, the quality of evidence was low: five studies had moderate risk, eleven studies had serious risk, and three studies had critical risk of bias.

CONCLUSIONS

Current evidence supports a significant association between history of PMS and development of PPD. Well-designed prospective studies are needed to further investigate this relationship.

Indicators Associated With Job Morale Among Physicians and Dentists in Low-Income and Middle-Income Countries: A Systematic Review and Meta-analysis

IMPORTANCE

Improving health care in low- and middle-income countries (LMICs) requires a workforce with positive job morale. However, the level of job morale in this population remains unclear.

OBJECTIVE

To analyze studies measuring the job morale of physicians and dentists working in LMICs, using levels of job burnout, job satisfaction, and job motivation as indicators of job morale.

DATA SOURCES

A comprehensive search of Scopus, PubMed, PsycINFO, EMBASE, Web of Science, and the Cochrane Library, from database inception to October 30, 2018, and gray literature was performed.

STUDY SELECTION

Studies were eligible if at least 50% of the sample were qualified physicians and/or dentists working in public health care settings in LMICs. Three indicators of job morale in this population were used: job burnout, job satisfaction, and job motivation. Of 12 324 records reviewed, 79 studies were included in the systematic review and 59 were eligible for the meta-analysis.

DATA EXTRACTION AND SYNTHESIS

Data were extracted independently by several investigators in accordance with the Meta-analyses of Observational Studies in Epidemiology (MOOSE) reporting guidelines. Random-effects meta-analyses, planned subgroup analyses, and metaregression were performed. The Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies was used to assess bias.

MAIN OUTCOMES AND MEASURES

Levels of job burnout, job satisfaction, and job motivation as indicators of job morale.

RESULTS

Overall, 12 324 records were identified. Of them, 80 records, representing 79 studies and involving 45 714 participants across 37 LMICs, met the inclusion criteria for the review; however, only 3 were from low-income countries. In 21 studies with 9092 participants working mainly in middle-income countries, 32% (95% CI, 27%-38%; I2 = 95.32%; P < .001) reported job burnout, and in 20 studies with 14 113 participants, 60% (95% CI, 53%-67%; I2 = 98.21%; P < .001) were satisfied with their job overall. Sufficient data were not available for a meta-analysis of job motivation.

CONCLUSIONS AND RELEVANCE

The findings suggest that, among physicians and dentists working mainly in middle-income countries, more than half reported having positive job morale. Positive job morale among physicians and dentists may help with recruitment and retention and thus support programs for improving health care in LMICs.

Prevalence of depressive symptoms in overweight and obese children and adolescents in mainland China: A meta-analysis of comparative studies and epidemiological surveys

BACKGROUND

Obesity is associated with a higher risk of depression in children and adolescents. This is a meta-analysis of studies examining depressive symptoms in overweight and obese children and adolescents in China.

METHODS

A systematic literature search was performed independently in both English (PubMed, EMBASE, Web of Science and Medline Complete) and Chinese (China National Knowledge Internet, WANFANG Data and WeiPu VIP) databases from their commencement date to December 31, 2018. The pooled prevalence of depressive symptoms was calculated using a random-effects model. Data analyses were performed with STATA Version 12.0, R Version 3.3.0 and R Studio Version 0.99.903.

RESULTS

Twenty-two epidemiological and 18 comparative studies were included in the meta-analysis. The overall prevalence of depressive symptoms was 24.02% (95% CI: 15.92%-33.16%) in obese children and adolescents and 22.61% (95% CI: 14.87%-31.34%) in overweigh children and adolescents. Obese children and adolescents were more likely to suffer from depressive symptoms (OR = 1.877, 95% CI: 1.459-2.415, P < 0.001) than their non-obese counterparts. The use of different screening scales for depressive symptoms was significantly associated with the prevalence of depressive symptoms.

CONCLUSIONS

Depressive symptoms are common in overweight and obese children and adolescents in China. Obese, but not overweight children and adolescents had higher risk of depressive symptoms. In order to lessen the risk of depressive symptoms, regular screening and effective interventions should be implemented to reduce obesity and overweight in this population.

Disparities in the management of cardiovascular risk factors in patients with psychiatric disorders: a systematic review and meta-analysis

BACKGROUND

The high cardiovascular (CV) morbidity and mortality reported for patients with psychiatric disorders may possibly be due to a poorer management of CV risk factors (CVRFs). However, these healthcare disparities remain poorly understood. In this paper, studies comparing the management of smoking, diabetes, hypertension and dyslipidaemia, in patients with and without depression, anxiety, schizophrenia, bipolar or personality disorder, were reviewed.

METHODS

Prospective studies comparing rates of screening, diagnosis, treatment and control of CVRFs were searched in PubMed, Embase, PsychInfo, Scopus and Web of Science (inception to January 2017). The Meta-analysis of Observational Studies in Epidemiology (MOOSE) criteria were used. Studies were assessed for quality. Wherever possible, meta-analyses were conducted to summarize the findings.

RESULTS

Twenty studies, out of the 18 333 references initially identified, were included. Most studies were heterogeneous in design. Two areas permitted meta-analyses: the pooled odds ratio for quitting smoking for those with depression was 0.64 (0.49-0.80) p < 0.001; the pooled difference of glycated haemoglobin for patients with type 2 diabetes and depression was 0.18 (0.06-0.31) p = 0.005. Individual studies showed associations between: schizophrenia and lower probability of having smoking habit recorded; schizoid personality disorder and higher probability of remaining non-smokers after quitting; anxiety and poorer control of type I diabetes; depression, anxiety or schizophrenia and lower probability of having a diagnosis of hypertension; schizophrenia or bipolar disorder and lower use of antihypertensive and lipid-lowering drugs.

CONCLUSIONS

A proactive clinical management, together with further studies, are needed to reduce the CV morbidity and mortality of patients with psychiatric disorders.

Methods to systematically review and meta-analyse observational studies: a systematic scoping review of recommendations

Background

Systematic reviews and meta-analyses of observational studies are frequently performed, but no widely accepted guidance is available at present. We performed a systematic scoping review of published methodological recommendations on how to systematically review and meta-analyse observational studies.

Methods

We searched online databases and websites and contacted experts in the field to locate potentially eligible articles. We included articles that provided any type of recommendation on how to conduct systematic reviews and meta-analyses of observational studies. We extracted and summarised recommendations on pre-defined key items: protocol development, research question, search strategy, study eligibility, data extraction, dealing with different study designs, risk of bias assessment, publication bias, heterogeneity, statistical analysis. We summarised recommendations by key item, identifying areas of agreement and disagreement as well as areas where recommendations were missing or scarce.

Results

The searches identified 2461 articles of which 93 were eligible. Many recommendations for reviews and meta-analyses of observational studies were transferred from guidance developed for reviews and meta-analyses of RCTs. Although there was substantial agreement in some methodological areas there was also considerable disagreement on how evidence synthesis of observational studies should be conducted. Conflicting recommendations were seen on topics such as the inclusion of different study designs in systematic reviews and meta-analyses, the use of quality scales to assess the risk of bias, and the choice of model (e.g. fixed vs. random effects) for meta-analysis.

Conclusion

There is a need for sound methodological guidance on how to conduct systematic reviews and meta-analyses of observational studies, which critically considers areas in which there are conflicting recommendations.

Electronic supplementary material

The online version of this article (10.1186/s12874-018-0495-9) contains supplementary material, which is available to authorized users.

Incidence, prognostic factors and impact of postoperative delirium after major vascular surgery: A meta-analysis and systematic review

Although postoperative delirium is a common complication and increases patient care needs, little is known about the predictors and outcomes of delirium in patients having vascular surgery. This review aimed to determine the incidence, prognostic factors and impact of postoperative delirium in vascular surgical patients. MEDLINE and EMBASE were systematically searched for articles published between January 2000 and January 2016 on delirium after vascular surgery. The primary outcome was the incidence of delirium. Secondary outcomes were contributing prognostic factors and impact of delirium. Study quality and risk of bias was assessed using the QUIPS tool for systematic reviews of prognostic studies, and MOOSE guidelines for reviews of observational studies. Quantitative analyses of extracted data were conducted using meta-analysis where possible to determine incidence of delirium and prognostic factors. A qualitative review of outcomes was performed. Fifteen articles were eligible for inclusion. Delirium incidence ranged between 5% and 39%. Meta-analysis found that patients with delirium were older than those without delirium (OR 3.6, p<0.001). Prognostic factors predicting delirium included increased age (OR 1.04, p<0.001), pre-existing cognitive impairment (OR 9.8, p=0.01), hypertension, pre-existing depression and open aortic surgery. Delirious patients remained in hospital 6 days longer ( p<0.001) and had more complications than patients without delirium. Data were limited on the impact of procedure complexity, endovascular compared to open surgery or type of anaesthetic. Postoperative delirium occurs frequently, resulting in major morbidity for vascular patients. Improved quality of prognostic studies may identify modifiable peri-operative factors to improve quality of care for vascular surgical patients.

Clinical risk factors for pre-eclampsia determined in early pregnancy: systematic review and meta-analysis of large cohort studies

OBJECTIVE

To develop a practical evidence based list of clinical risk factors that can be assessed by a clinician at ≤ 16 weeks' gestation to estimate a woman's risk of pre-eclampsia.

DESIGN

Systematic review and meta-analysis of cohort studies.

DATA SOURCES

PubMed and Embase databases, 2000-15.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Cohort studies with ≥ 1000 participants that evaluated the risk of pre-eclampsia in relation to a common and generally accepted clinical risk factor assessed at ≤ 16 weeks' gestation.

DATA EXTRACTION

Two independent reviewers extracted data from included studies. A pooled event rate and pooled relative risk for pre-eclampsia were calculated for each of 14 risk factors.

RESULTS

There were 25,356,688 pregnancies among 92 studies. The pooled relative risk for each risk factor significantly exceeded 1.0, except for prior intrauterine growth restriction. Women with antiphospholipid antibody syndrome had the highest pooled rate of pre-eclampsia (17.3%, 95% confidence interval 6.8% to 31.4%). Those with prior pre-eclampsia had the greatest pooled relative risk (8.4, 7.1 to 9.9). Chronic hypertension ranked second, both in terms of its pooled rate (16.0%, 12.6% to 19.7%) and pooled relative risk (5.1, 4.0 to 6.5) of pre-eclampsia. Pregestational diabetes (pooled rate 11.0%, 8.4% to 13.8%; pooled relative risk 3.7, 3.1 to 4.3), prepregnancy body mass index (BMI) >30 (7.1%, 6.1% to 8.2%; 2.8, 2.6 to 3.1), and use of assisted reproductive technology (6.2%, 4.7% to 7.9%; 1.8, 1.6 to 2.1) were other prominent risk factors.

CONCLUSIONS

There are several practical clinical risk factors that, either alone or in combination, might identify women in early pregnancy who are at "high risk" of pre-eclampsia. These data can inform the generation of a clinical prediction model for pre-eclampsia and the use of aspirin prophylaxis in pregnancy.

Prognostic impact of elevation of vascular endothelial growth factor family expression in patients with non-small cell lung cancer: an updated meta-analysis

BACKGROUND

The vascular endothelial growth factor family has been implicated in tumorigenesis and metastasis. The prognostic value of each vascular endothelial growth factor family member, particular VEGF/ VEGFR co-expression, in patients with non-small lung cancer remains controversial.

MATERIALS AND METHODS

Relevant literature was identified by searching PubMed, EMBASE and Web of Science. Studies evaluating expression of VEGFs and/or VEGFRs by immunohistochemistry or ELISA in lung cancer tissue were eligible for inclusion. Hazard ratios (HRs) and 95% confidence intervals (CIs) from individual study were pooled by using a fixed- or random-effect model, heterogeneity and publication bias analyses were also performed.

RESULTS

74 studies covering 7,631 patients were included in the meta-analysis. Regarding pro-angiogenesis factors, the expression of VEGFA (HR=1.633, 95%CI: 1.490-1.791) and VEGFR1 (HR=1.924, 95%CI: 1.220-3.034) was associated separately with poor survival. Especially, VEGFA over-expression was an independent prognostic factor in adenocarcinoma (ADC) (HR=1.775, 95%CI: 1.384-2.275) and SCC (HR=2.919, 95%CI: 2.060-4.137). Co-expression of VEGFA/VEGFR2 (HR=2.011, 95%CI: 1.405-2.876) was also significantly associated with worse survival. For lymphangiogenesis factors, the expression of VEGFC (HR=1.611, 95%CI: 1.407-1.844) predicted a poor prognosis. Co-expression of VEGFC/VEGFR3 (HR=2.436, 95%CI: 1.468-4.043) emerged as a preferable prognostic marker.

CONCLUSIONS

The expression of VEGFA (particularly in SCC and early stage NSCLC), VEGFC, VEGFR1 indicates separately an unfavorable prognosis in patients with NSCLC. Co-expression VEGFA/ VEGFR2 is comparable with VEGFC/VEGFR3, both featuring sufficient discrimination value as preferable as prognostic biologic markers.

The prevalence of gestational diabetes mellitus among Aboriginal and Torres Strait Islander women in Australia: a systematic review and meta-analysis

INTRODUCTION

Gestational diabetes mellitus (GDM) is an important and increasing health problem. This study aims to investigate and explain the marked variation in reported GDM prevalence among Australian Indigenous women.

MATERIALS AND METHODS

We searched five databases to August 2013 for studies of GDM prevalence; two people independently assessed search results, extracted data, and appraised risk of bias. Meta-analysis was conducted, and between-study heterogeneity examined using subgroup analyses. Within-study findings were synthesized narratively.

RESULTS

The pooled GDM prevalence from 23 of the 25 total studies (5.74%, 4.78-6.71) was similar to that reported in national studies, but heterogeneity was substantial (I(2)  = 97%), making conclusions from between-study comparisons difficult. The greatest reductions in heterogeneity were seen within subgroups using localized diagnostic criteria (I(2)  = 43%, 3 studies), universal screening (I(2)  = 58%) and some jurisdictions, probably reflecting proxy measures of increased consistency in diagnostic and screening methods. Insufficient data were available to assess the effect of factors such as rurality, diagnostic criteria, study design and data sources on prevalence. Synthesis of within-study findings showed: higher age-adjusted prevalences of GDM in Indigenous versus non-Indigenous women; Indigenous women have greater increases in prevalence with maternal age; and non-Indigenous women appear to have a steeper increase in GDM prevalence over time. Prevalence increased almost fourfold in two studies following introduction of universal screening when compared with selective risk-based screening, although numbers were small.

DISCUSSION/CONCLUSIONS

The published GDM prevalence among Indigenous women varies markedly, probably due to variation in diagnostic and screening practices.

Cardiac ion channelopathies and the sudden infant death syndrome

The sudden infant death syndrome (SIDS) causes the sudden death of an apparently healthy infant, which remains unexplained despite a thorough investigation, including the performance of a complete autopsy. The triple risk model for the pathogenesis of SIDS points to the coincidence of a vulnerable infant, a critical developmental period, and an exogenous stressor. Primary electrical diseases of the heart, which may cause lethal arrhythmias as a result of dysfunctioning cardiac ion channels (“cardiac ion channelopathies”) and are not detectable during a standard postmortem examination, may create the vulnerable infant and thus contribute to SIDS. Evidence comes from clinical correlations between the long QT syndrome and SIDS as well as genetic analyses in cohorts of SIDS victims (“molecular autopsy”), which have revealed a large number of mutations in ion channel-related genes linked to inheritable arrhythmogenic syndromes, in particular the long QT syndrome, the short QT syndrome, the Brugada syndrome, and catecholaminergic polymorphic ventricular tachycardia. Combining data from population-based cohort studies, it can be concluded that at least one out of five SIDS victims carries a mutation in a cardiac ion channel-related gene and that the majority of these mutations are of a known malignant phenotype.

Sudden infant death syndrome and prone sleeping position

In this review, we describe the epidemiological work conducted by ourselves and others on prone sleep position and sudden infant death. What we have learned since 1990 is that the prone sleep position was a major component of a casual pathway that was operating in over half of the SIDS deaths that were occurring in developed countries at the end of the 1980. It has been estimated that advice to place infants supine to sleep may have saved in the order of 850 infants annually in Australia and other countries. The story of the SIDS epidemic is an example of the contribution that epidemiology can make to the understanding and prevention of an important public health problem.

Meta-analysis of factors related to health services that predict treatment default by tuberculosis patients

The identification of factors that predict tuberculosis (TB) treatment default can help control this problem. The current study used a systematic review to investigate associations between TB treatment default and previously studied factors related to health services. Abstracts were searched in the MEDLINE and LILACS databases and in the bibliography of the full texts under evaluation. Studies were included if TB treatment default was evaluated by comparing two or more groups and data could be extracted. A total of 41 studies were included for combining data. It was possible to combine five exposures: "difficult access to health services"; "need for hospitalization"; "training or support for adherence"; "delay in initiating treatment"; "long wait before medical attendance". "Difficult access to health services", "training or support for adherence", and "need for hospitalization" were associated with TB treatment default. All exposures demonstrated heterogeneity, which was only explained in one. Publication bias was only detected for one exposure.

[Systematic reviews and meta-analysis]

Over the past years, systematic reviews and meta-analyses have led to significant changes in clinical medicine and health policy. To date, they can be viewed as the most objective instruments to answer clinical as well health policy questions. In addition, systematic reviews are an important tool to synthesize the enormous amount of new medical knowledge into a manageable format. Nevertheless, the methodological quality of published systematic reviews and meta-analyses varies and biased results can be misleading. Therefore, it is important for readers of systematic reviews to critically evaluate the underlying methods, to be able to assess the validity of their findings. This manuscript is part of a methods series of the Wiener Medizinische Wochenschrift. It summarizes the methodological hallmarks of systematic reviews and meta-analyses to provide readers with the methodological background necessary to critically evaluate systematic reviews and meta-analyses.

Nonsteroidal anti-inflammatory drugs and lung cancer risk: a population-based case control study

BACKGROUND

It remains unknown whether nonsteroidal anti-inflammatory drugs (NSAIDs) confer a protective effect against lung cancer development. We examined the relationship between NSAID exposure and subsequent lung cancer development in a large statewide, population-based cohort.

DESIGN

Nested case-control study in the Tennessee Medicaid population from 1990 to 2000.

METHODS

Lung cancer cases were identified using a statewide computerized claims database. Each time a case was identified, age- and sex-matched controls were randomly selected from the available source population. A detailed pharmacy database quantified nonsteroidal anti-inflammatory drug (NSAID) exposure during the 5 years before cancer diagnosis, and conditional logistic regression was used to examine the relationship between NSAID exposure and lung cancer development. Identical analyses were repeated in a subpopulation of high-risk individuals with chronic obstructive pulmonary disease (COPD).

RESULTS

303,399 persons were enrolled in the study population. During 1.9 million person-years of follow-up (median 6.3 years per person), 3,370 lung cancer cases were identified. Among those ever using NSAIDs, the adjusted odds ratio of developing lung cancer was 1.03 (95% confidence interval: 0.94-1.12). Among those using >24 months of NSAIDs in the 5 years before lung cancer diagnosis, the adjusted odds ratio for lung cancer was 0.96 (95% confidence interval: 0.82-1.11), and no protective effect was demonstrated in any NSAID exposure stratum. Similarly, among the 2519 high-risk individuals with chronic obstructive pulmonary disease, no significant protective effect from NSAIDs was noted.

CONCLUSION

This large statewide, population-based study did not demonstrate a protective effect of NSAIDs on lung cancer development in either the general or high-risk chronic obstructive pulmonary disease populations.

Infant sleeping position and the sudden infant death syndrome: systematic review of observational studies and historical review of recommendations from 1940 to 2002

BACKGROUND

Before the early 1990s, parents were advised to place infants to sleep on their front contrary to evidence from clinical research.

METHODS

We systematically reviewed associations between infant sleeping positions and sudden infant death syndrome (SIDS), explored sources of heterogeneity, and compared findings with published recommendations.

RESULTS

By 1970, there was a statistically significantly increased risk of SIDS for front sleeping compared with back (pooled odds ratio (OR) 2.93; 95% confidence interval (CI) 1.15, 7.47), and by 1986, for front compared with other positions (five studies, pooled OR 3.00; 1.69-5.31). The OR for front vs the back position was reduced as the prevalence of the front position in controls increased. The pooled OR for studies conducted before advice changed to avoid front sleeping was 2.95 (95% CI 1.69-5.15), and after was 6.91 (4.63-10.32). Sleeping on the front was recommended in books between 1943 and 1988 based on extrapolation from untested theory.

CONCLUSIONS

Advice to put infants to sleep on the front for nearly a half century was contrary to evidence available from 1970 that this was likely to be harmful. Systematic review of preventable risk factors for SIDS from 1970 would have led to earlier recognition of the risks of sleeping on the front and might have prevented over 10 000 infant deaths in the UK and at least 50 000 in Europe, the USA, and Australasia. Attenuation of the observed harm with increased adoption of the front position probably reflects a "healthy adopter" phenomenon in that families at low risk of SIDS were more likely to adhere to prevailing health advice. This phenomenon is likely to be a general problem in the use of observational studies for assessing the safety of health promotion.

Variability of breast cancer risk in observational studies of hormone replacement therapy: a meta-regression analysis

OBJECTIVES

A re-analysis of data from 51 epidemiological studies reported a significant 14% increase in the risk of breast cancer associated with the use of hormone replacement therapy (HRT). Unlike randomized trials, these observational studies varied in design and methods. This study was conducted to explore the impact of study design factors on the rate ratio.

METHODS

We performed a meta-regression analysis of 39 epidemiological studies of HRT and breast cancer. The rate ratio of breast cancer associated with ever use of HRT was evaluated in relation to study design, study period, country, primary study objective, method of exposure measurement, age control, adjustment factors related to reproduction and menopause, and the presence of breast cancer surveillance. We used stepwise multiple regression analysis, weighted by the inverse of the variance of the logarithm of the rate ratio, to estimate ratios of rate ratios for these factors.

RESULTS

Exposure measured by personal interview and/or medical record review was associated with a 14% lower rate ratio estimate as compared with telephone interview or self-administered questionnaire (P = 0.018). Among studies that did not adjust for age at menopause, the rate ratio was 12% lower if the primary objective was HRT effect than not (P = 0.016), while it was 43% higher among studies that adjusted for age at menopause (P = 0.042). An index that included as six desirable design features, breast cancer surveillance, matching of controls, more reliable exposure information, adjustment for age at menopause and reproductive risk factors, and as primary objective the effect of HRT suggests that studies with none of these properties would lead to a rate ratio estimate of 1.14 (95% CI: 1.00-1.29) while studies with all six properties would produce a rate ratio of 0.98 (95% CI: 0.83-1.15).

CONCLUSIONS

Design factors of epidemiological studies could be an alternative explanation for the reported 14% increase in the risk of breast cancer associated with the use of HRT.

A multivariate "time based" analysis of SIDS risk factors

AIMS

To investigate the influence of analytical design on the variability of published results in studies of sudden infant death syndrome (SIDS).

METHODS

The results of a prospective case-control study, of 203 cases of SIDS, and 622 control infants are presented. All variables significant on univariate analysis were included in a multivariate model analysed in nine stages, starting with sociodemographic variables, then sequentially and cumulatively adding variables relating to pregnancy history, current pregnancy, birth, the interval from birth to the week prior to death, the last week, the last 48 hours, and the last sleep period. A ninth stage was created by adding placed to sleep prone for the last sleep period.

RESULTS

As additional variables are added, previously published SIDS risk factors emerged such as social deprivation, young maternal age, > or =3 previous live births, maternal smoking and drinking, urinary tract infection in pregnancy, reduced birth weight, and the infant having an illness, regurgitation, being sweaty, or a history of crying/colic in the interval from birth to the week before death, with co-sleeping and the lack of regular soother use important in the last sleep period. As the model progressed through stages 1-9, many significant variables became non-significant (social deprivation, young maternal age, maternal smoking and drinking) and in stage 9 the addition of placed to sleep prone for the last sleep period caused > or =3 previous live births and a reduced birth weight to become significant.

CONCLUSION

The variables found to be significant in a case-control study, depend on what is included in a multivariate model.

Cancer risks associated with the diagnosis of infertility

The effects of infertility and its treatment on cancer risk are of concern to many infertile couples. Infertile women appear to be at no higher risk for breast cancer although they may be more at risk for cancers of the uterus, particularly if they have ovulation disorders. Most studies show no increase in the risk of invasive ovarian cancer in infertile women, but ovarian tumours of borderline malignancy are more common. There seems to be no overall increase in cancer risk associated with fertility drug treatment, but questions remain about risk in subgroups of infertile women. Male infertility has been associated with an increased risk of testis cancer. Cancer incidence in children born after fertility treatment appears to be similar to that in the general population. Discussion of cancer risks in the context of other reproductive and community risks can be helpful to patients.