Selective reporting of adjusted estimates in observational epidemiology studies: reasons and implications for meta-analyses

Toward Open and Reproducible Epidemiology

Starting in the 2010s, researchers in the experimental social sciences rapidly began to adopt increasingly open and reproducible scientific practices. These practices include publicly sharing deidentified data when possible, sharing analytical code, and preregistering study protocols. Empirical evidence from the social sciences suggests such practices are feasible, can improve analytical reproducibility, and can reduce selective reporting. In academic epidemiology, adoption of open-science practices has been slower than in the social sciences (with some notable exceptions, such as registering clinical trials). Epidemiologic studies are often large, complex, conceived after data have already been collected, and difficult to replicate directly by collecting new data. These characteristics make it especially important to ensure their integrity and analytical reproducibility. Open-science practices can also pay immediate dividends to researchers' own work by clarifying scientific reasoning and encouraging well-documented, organized workflows. We consider how established epidemiologists and early-career researchers alike can help midwife a culture of open science in epidemiology through their research practices, mentorship, and editorial activities.

Comorbidity between mood and substance-related disorders: A systematic review and meta-analysis

BACKGROUND AND OBJECTIVES

Evidence indicates that mood disorders often co-occur with substance-related disorders. However, pooling comorbidity estimates can be challenging due to heterogeneity in diagnostic criteria and in the overall study design. The aim of this study was to systematically review and, where appropriate, meta-analyse estimates related to the pairwise comorbidity between mood disorders and substance-related disorders, after sorting these estimates by various study designs.

METHODS

We searched PubMed (MEDLINE), Embase, CINAHL and Web of Science for publications between 1980 and 2017 regardless of geographical location and language. We meta-analysed estimates from original articles in 4 broadly defined mood and 35 substance-related disorders.

RESULTS

After multiple eligibility steps, we included 120 studies for quantitative analysis. In general, regardless of variations in diagnosis type, temporal order or use of adjustments, there was substantial comorbidity between mood and substance-related disorders. We found a sixfold elevated risk between broadly defined mood disorder and drug dependence (odds ratio = 5.7) and fivefold risk between depression and cannabis dependence (odds ratio = 4.9) while the highest pooled estimate, based on period prevalence risk, was found between broadly defined dysthymic disorder and drug dependence (odds ratio = 11.3). Based on 56 separate meta-analyses, all pooled odds ratios were above 1, and 46 were significantly greater than 1 (i.e. the 95% confidence intervals did not include 1).

CONCLUSION

This review found robust and consistent evidence of an increased risk of comorbidity between many combinations of mood and substance-related disorders. We also identified a number of under-researched mood and substance-related disorders, suitable for future scrutiny. This review reinforces the need for clinicians to remain vigilant in order to promptly identify and treat these common types of comorbidity.

The confounder matrix: A tool to assess confounding bias in systematic reviews of observational studies of etiology

Systematic reviews and meta-analyses are essential for drawing conclusions regarding etiologic associations between exposures or interventions and health outcomes. Observational studies comprise a substantive source of the evidence base. One major threat to their validity is residual confounding, which may occur when component studies adjust for different sets of confounders, fail to control for important confounders, or have classification errors resulting in only partial control of measured confounders. We present the confounder matrix-an approach for defining and summarizing adequate confounding control in systematic reviews of observational studies and incorporating this assessment into meta-analyses. First, an expert group reaches consensus regarding the core confounders that should be controlled and the best available method for their measurement. Second, a matrix graphically depicts how each component study accounted for each confounder. Third, the assessment of control adequacy informs quantitative synthesis. We illustrate the approach with studies of the association between short interpregnancy intervals and preterm birth. Our findings suggest that uncontrolled confounding, notably by reproductive history and sociodemographics, resulted in exaggerated estimates. Moreover, no studies adequately controlled for all core confounders, so we suspect residual confounding is present, even among studies with better control. The confounder matrix serves as an extension of previously published methodological guidance for observational research synthesis, enabling transparent reporting of confounding control and directly informing meta-analysis so that conclusions are drawn from the best available evidence. Widespread application could raise awareness about gaps across a body of work and allow for more valid inference with respect to confounder control.

McGrath J. Co-morbidity between mood and anxiety disorders: A systematic review and meta-analysis

There is consistent evidence that mood disorders often co-occur with anxiety disorders, however, the strength of the association of these two broad groups of disorders has been challenging to summarize across different studies. The aim was to conduct a meta-analysis of publications reporting on the pairwise comorbidity between mood and anxiety disorders after sorting into comparable study types. We searched MEDLINE, Embase, CINAHL, Web of Science, and the grey literature for publications between 1980 and 2017 regardless of geographical locations and languages. We meta-analyzed estimates from original articles after sorting by: (a) broad or narrow diagnostic criteria, (b) study time-frame, and (c) estimates with or without covariate adjustments. Over 43 000 unique studies were identified through electronic searches, of which 391 were selected for full-text review. Finally, 171 studies were eligible for inclusion, including 53 articles from additional snowball searching. In general, regardless of variations in diagnosis type, study time-frame, temporal order, or use of adjustments, there was substantial comorbidity between mood and anxiety disorders. Based on the entire 90 separate meta-analyses, the median OR was 6.1 (range 1.5-18.7). Of these estimates, all 90 were above 1, and 87 were significantly greater than 1 (i.e., the 95% confidence intervals did not include 1). Fourteen of the 90 pooled estimates had ORs that were greater than 10. This systematic review found robust and consistent evidence of comorbidity between broadly defined mood and anxiety disorders. Clinicians should be vigilant for the prompt identification and treatment of this common type of comorbidity.

17α-Hydroxyprogesterone Caproate and the Risk of Glucose Intolerance in Pregnancy: A Systematic Review and Meta-analysis

OBJECTIVE

To evaluate whether 17α-hydroxyprogesterone caproate use in preventing preterm birth increases the risk of gestational diabetes mellitus (GDM).

DATA SOURCES

Electronic databases (MEDLINE, Scopus, ClinicalTrials.gov, PROSPERO, EMBASE, Scielo and the Cochrane Central Register of Controlled Trials) were searched for studies published before October 2018. Keywords included "gestational diabetes," "preterm birth," "pregnancy," and "17-hydroxyprogesterone caproate."

METHODS OF STUDY SELECTION

Studies comparing 17α-hydroxyprogesterone caproate with unexposed control groups in women with singleton gestation and a history of a prior spontaneous preterm birth were included. The primary outcome was the development of GDM. Secondary outcomes included abnormal 1-hour, 50-g glucose screen results and mean venous blood glucose levels. Summary estimates were reported as mean differences and 95% CI for continuous variables or relative risk (RR) with 95% CI for dichotomous outcomes. Meta-analysis was performed using the random effects model of DerSimonian and Laird.

TABULATION, INTEGRATION AND RESULTS

Six studies, four of which were cohort studies, met inclusion criteria and were included in the final meta-analysis. Of the 5,053 women, 1,538 (30.4%) received 17α-hydroxyprogesterone caproate and 3,515 (69.6%) were in unexposed control groups. The overall rate of GDM in women exposed to 17α-hydroxyprogesterone caproate was 10.9% vs 6.1% in women who were not exposed (RR 1.77, 95% CI 1.22-2.55). After exclusion of the cohort studies, the summary estimate of effect was nonsignificant among women who had been randomly allocated to 17α-hydroxyprogesterone caproate (RR 1.21, 95% CI 0.63-2.36).

CONCLUSION

Women with singleton gestations receiving weekly 17α-hydroxyprogesterone caproate for recurrent preterm birth prevention had a significantly higher incidence of abnormal glucose test results and GDM compared with those in unexposed control groups, a finding that did not hold among women who had been randomly allocated to 17α-hydroxyprogesterone caproate.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO, CRD42016041694.

Adjuvant 17-hydroxyprogesterone caproate in women with history-indicated cerclage: A systematic review and meta-analysis

INTRODUCTION

The purpose of this study was to evaluate whether there are additional benefits of 17-hydroxyprogesterone caproate (17-OHPC) supplementation in preventing recurrent spontaneous preterm birth in women with a prophylactic cerclage.

MATERIAL AND METHODS

Electronic databases (MEDLINE, Scopus, ClinicalTrials.gov, PROSPERO, EMBASE, Scielo and the Cochrane Central Register of Controlled Trials) were searched for studies published before June 2018. Keywords included "preterm birth", "prophylactic cerclage", "history-indicated cerclage", "pregnancy" and "17-hydroxyprogesterone caproate". Studies comparing history-indicated cerclage alone with cerclage+17-OHPC were included. The primary outcome measure was preterm birth at <24 weeks of gestation. Secondary outcome measures include preterm birth at <28 weeks, <32 weeks and <37 weeks of gestation, respiratory distress syndrome, necrotizing enterocolitis, fetal birthweight, neonatal intensive care unit stay, mean gestational age at delivery, fetal/neonatal death, neurological morbidity (intraventricular hemorrhage plus periventricular leukomalacia), neonatal sepsis and a composite of severe neonatal morbidity. Severe neonatal morbidity was defined as a composite measure of periventricular leukomalacia, intraventricular hemorrhage (grades III and IV), necrotizing enterocolitis or respiratory distress syndrome. Meta-analysis was performed using the random-effects model of DerSimonian and Laird. Risk of bias and quality assessment were performed using the ROBINS-I and GRADE tools, respectively. PROSPERO Registration Number: CRD42018094559.

RESULTS

Five studies met the inclusion criteria and were included in the final analysis. Of the 546 women, 357 (75%) received history-indicated cerclage alone and 189 (35%) received adjuvant 17-OHPC. The composite endpoint, severe neonatal morbidity, was present in 84 of 1515 neonates. Though there was a trend toward a reduced risk of preterm birth, the summary estimate of effect was not statistically significant when comparing cerclage alone with cerclage+17-OHPC at <24 weeks (relative risk [RR] .86, 95% confidence interval [CI] .45-1.65). Similarly, we found no differences in preterm birth at <37 weeks (RR .90, 95% CI .70-1.17) and <28 weeks (RR .85, 95% CI .54-1.32) when comparing cerclage alone with cerclage+17-OHPC. There were no differences in fetal birthweight, respiratory distress syndrome or necrotizing enterocolitis comparing cerclage alone with cerclage+17-OHPC.

CONCLUSIONS

Intramuscular 17-OHPC in combination with prophylactic cerclage in women with prior preterm birth had no synergistic effect in reducing spontaneous recurrent preterm birth or improving perinatal outcomes.

Behavioral impact of return of genetic test results for complex disease: Systematic review and meta-analysis

OBJECTIVE

Advances in genomewide association studies have made possible the return of genetic risk results for complex diseases. Two concerns about these results are (a) negative psychological consequences and (b) viewing probabilistic results as deterministic, leading to misinterpretation and inappropriate decisions. The present study evaluates these concerns through a meta-analytic review of existing literature.

METHOD

Seventeen genetic testing studies of complex disease, including 1,171 participants and reporting 195 effects, 104 of which were unadjusted for covariates, were meta-analyzed under a random effects model. Diseases included Alzheimer's, cardiovascular and coronary heart disease, lung cancer, melanoma, thrombophilia, and type II diabetes. Six domains of behavioral-psychological reactions were examined.

RESULTS

Carriers showed significantly increased self-reported behavior change compared to noncarriers when assessed 6 months or later after results return (Hedges's g = .36, p = .019).

CONCLUSIONS

Return of genetic testing results for complex disease does not strongly impact self-reported negative behavior or psychological function of at-risk individuals. Return of results does appear to moderately increase self-reported healthy behavior in carriers, although research on objectively observed behavior change is needed. This is a growing area of research, with preliminary results suggesting potential positive implications of genetic testing for complex disease on behavior change. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Trends in Epidemiology of Pediatric Inflammatory Bowel Disease in Canada: Distributed Network Analysis of Multiple Population-Based Provincial Health Administrative Databases

OBJECTIVES

The incidence of pediatric-onset inflammatory bowel disease (IBD) is increasing worldwide. We used population-based health administrative data to determine national Canadian IBD incidence, prevalence, and trends over time of childhood-onset IBD.

METHODS

We identified children <16 years (y) diagnosed with IBD 1999-2010 from health administrative data in five provinces (Alberta, Manitoba, Nova Scotia, Ontario, Quebec), comprising 79.2% of the Canadian population. Standardized incidence and prevalence were calculated per 100,000 children. Annual percentage change (APC) in incidence and prevalence were determined using Poisson regression analysis. Provincial estimates were meta-analyzed using random-effects models to produce national estimates.

RESULTS

5,214 incident cases were diagnosed during the study period (3,462 Crohn's disease, 1,382 ulcerative colitis, 279 type unclassifiable). The incidence in Canada was 9.68 (95% CI 9.11 to 10.25) per 100,000 children. Incidence was similar amongst most provinces, but higher in Nova Scotia. APC in incidence did not significantly change over the study period in the overall cohort (+2.06%, 95% CI -0.64% to +4.76%). However, incidence significantly increased in children aged 0-5y (+7.19%, 95% +2.82% to +11.56%). Prevalence at the end of the study period in Canada was 38.25 (95% CI 35.78 to 40.73) per 100,000 children. Prevalence increased significantly over time, APC +4.56% (95% CI +3.71% to +5.42%).

CONCLUSIONS

Canada has amongst the highest incidence of childhood-onset IBD in the world. Prevalence significantly increased over time. Incidence was not statistically changed with the exception of a rapid increase in incidence in the youngest group of children.

Selective serotonin reuptake inhibitor (SSRI) use during pregnancy and risk of preterm birth: a systematic review and meta-analysis

BACKGROUND

Depression is a prevalent condition in pregnancy affecting about 10% of women. Maternal depression has been associated with an increase in preterm births (PTB), low birthweight and fetal growth restriction, and postnatal complications. Available treatments for depressive disorders are psychotherapeutic interventions and antidepressant medications including selective serotonin inhibitors (SSRIs). SSRI use during pregnancy has been associated with several fetal and neonatal complications; so far, however, the risk of PTB in women using SSRIs during pregnancy is still a subject of debate.

OBJECTIVE

To evaluate the risk of preterm birth (PTB) in cases of exposure to SSRIs during pregnancy.

SEARCH STRATEGY

Electronic databases (MEDLINE, Scopus, ClinicalTrials.gov, the PROSPERO International Prospective Register of Systematic Reviews, EMBASE and the Cochrane Central Register of Controlled Trials) were searched from their inception until May 2015 with the use of a combination of the following text words 'depression', 'pregnancy', 'exposure', 'antidepressant', 'SSRI', 'selective serotonin reuptake inhibitor', 'preterm birth', 'small for gestational age' and 'prematurity'.

SELECTION CRITERIA

We included studies evaluating the effect of SSRIs exposure in utero and pregnancy outcomes. All cohort and case-control studies were eligible to be included if they reported the incidence of PTB after any exposure to SSRIs and had a comparison group of unexposed pregnant women. Studies without a control group were excluded.

DATA COLLECTION AND ANALYSIS

The primary outcome was the incidence of PTB <37 weeks. Subgroup analysis of studies in which controls were defined as women with depression but without SSRI exposure during pregnancy were planned.

MAIN RESULTS

Eight studies (1 237 669 women) were included: 93 982 in the exposure group and 1 143 687 in the control group. After adjusting for confounders, the incidence of PTB was significantly higher in the group of women treated with SSRIs compared with controls (i.e. both women with depression but without SSRI exposure and women without depression) (adjusted OR (aOR) 1.24, 95% CI 1.09-1.41). In the subgroup analysis of studies in which controls were defined as women with depression but without SSRI exposure during pregnancy, an increased risk of PTB (6.8 versus 5.8%; OR 1.17, 95% CI 1.10-1.25) in the SSRI group was found compared with controls (i.e. depressed women treated with psychotherapy alone).

CONCLUSIONS

Women who received SSRIs during pregnancy had a significantly higher risk of developing PTB compared with controls. This higher risk remained significant even when comparing depressed women on SSRI with women not on SSRI.

TWEETABLE ABSTRACT

Selective serotonin reuptake inhibitors may be associated with preterm birth.

Prior uterine evacuation of pregnancy as independent risk factor for preterm birth: a systematic review and metaanalysis

BACKGROUND

Preterm birth (PTB) is the number one cause of perinatal mortality. Prior surgery on the cervix is associated with an increased risk of PTB. History of uterine evacuation, by either induced termination of pregnancy (I-TOP) or spontaneous abortion (SAB), which involve mechanical and/or osmotic dilatation of the cervix, has been associated with an increased risk of PTB in some studies but not in others.

OBJECTIVE

The objective of the study was to evaluate the risk of PTB among women with a history of uterine evacuation for I-TOP or SAB.

DATA SOURCES

Electronic databases (MEDLINE, Scopus, ClinicalTrials.gov, EMBASE, and Sciencedirect) were searched from their inception until January 2015 with no limit for language.

STUDY ELIGIBILITY CRITERIA

We included all studies of women with prior uterine evacuation for either I-TOP or SAB, compared with a control group without a history of uterine evacuation, which reported data about the subsequent pregnancy.

STUDY APPRAISAL AND SYNTHESIS METHODS

The primary outcome was the incidence of PTB < 37 weeks. Secondary outcomes were incidence of low birthweight (LBW) and small for gestational age (SGA). We planned to assess the primary and the secondary outcomes in the overall population as well as in studies on I-TOP and SAB separately. The pooled results were reported as odds ratio (OR) with 95% confidence interval (CI).

RESULTS

We included 36 studies in this metaanalysis (1,047,683 women). Thirty-one studies reported data about prior uterine evacuation for I-TOP, whereas 5 studies reported data for SAB. In the overall population, women with a history of uterine evacuation for either I-TOP or SAB had a significantly higher risk of PTB (5.7% vs 5.0%; OR, 1.44, 95% CI, 1.09-1.90), LBW (7.3% vs 5.9%; OR, 1.41, 95% CI, 1.22-1.62), and SGA (10.2% vs 9.0%; OR, 1.19, 95% CI, 1.01-1.42) compared with controls. Of the 31 studies on I-TOP, 28 included 913,297 women with a history of surgical I-TOP, whereas 3 included 10,253 women with a prior medical I-TOP. Women with a prior surgical I-TOP had a significantly higher risk of PTB (5.4% vs 4.4%; OR, 1.52, 95% CI, 1.08-2.16), LBW (7.3% vs 5.9%; OR, 1.41, 95% CI, 1.22-1.62), and SGA (10.2% vs 9.0%; OR, 1.19, 95% CI, 1.01-1.42) compared with controls. Women with a prior medical I-TOP had a similar risk of PTB compared with those who did not have a history of I-TOP (28.2% vs 29.5%; OR, 1.50, 95% CI, 1.00-2.25). Five studies, including 124,133 women, reported data about a subsequent pregnancy in women with a prior SAB. In all of the included studies, the SAB was surgically managed. Women with a prior surgical SAB had a higher risk of PTB compared with those who did not have a history of SAB (9.4% vs 8.6%; OR, 1.19, 95% CI, 1.03-1.37).

CONCLUSION

Prior surgical uterine evacuation for either I-TOP or SAB is an independent risk factor for PTB. These data warrant caution in the use of surgical uterine evacuation and should encourage safer surgical techniques as well as medical methods.

Celiac disease and obstetric complications: a systematic review and metaanalysis

The aim of this metaanalysis was to evaluate the risk of the development of obstetric complications in women with celiac disease. We searched electronic databases from their inception until February 2015. We included all cohort studies that reported the incidence of obstetric complications in women with celiac disease compared with women without celiac disease (ie, control group). Studies without a control group and case-control studies were excluded. The primary outcome was defined a priori and was the incidence of a composite of obstetric complications that included intrauterine growth restriction, small for gestational age, low birthweight, preeclampsia and preterm birth. Secondary outcomes included the incidence of preterm birth, intrauterine growth restriction, stillbirth, preeclampsia, small for gestational age, and low birthweight. The review was registered with PROSPERO (CRD42015017263) before data extraction. All authors were contacted to obtain the original databases and perform individual participant data metaanalysis. Primary and secondary outcomes were assessed in the aggregate data analysis and in the individual participant data metaanalysis. We included 10 cohort studies (4,844,555 women) in this metaanalysis. Four authors provided the entire databases for the individual participant data analysis. Because none of the included studies stratified data for the primary outcome (ie, composite outcome), the assessment of this outcome for the aggregate analysis was not feasible. Aggregate data analysis showed that, compared with women in the control group, women with celiac disease (both treated and untreated) had a significantly higher risk of the development of preterm birth (adjusted odds ratio, 1.35; 95% confidence interval, 1.09-1.66), intrauterine growth restriction (odds ratio, 2.48; 95% confidence interval, 1.32-4.67), stillbirth (odds ratio, 4.84; 95% confidence interval, 1.08-21.75), low birthweight (odds ratio, 1.63; 95% confidence interval, 1.06-2.51), and small for gestational age (odds ratio, 4.52; 95% confidence interval, 1.02-20.08); no statistically significant difference was found in the incidence of preeclampsia (odds ratio, 2.45; 95% confidence interval, 0.90-6.70). The risk of preterm birth was still significantly higher both in the subgroup analysis of only women with diagnosed and treated celiac disease (odds ratio, 1.26; 95% confidence interval, 1.06-1.48) and in the subgroup analysis of only women with undiagnosed and untreated celiac disease (odds ratio, 2.50; 95% confidence interval; 1.06-5.87). Women with diagnosed and treated celiac disease had a significantly lower risk of the development of preterm birth, compared with undiagnosed and untreated celiac disease (odds ratio, 0.80; 95% confidence interval, 0.64-0.99). The individual participant data metaanalysis showed that women with celiac disease had a significantly higher risk of composite obstetric complications compared with control subjects (odds ratio, 1.51; 95% confidence interval, 1.17-1.94). Our individual participant data concurs with the aggregate analysis for all the secondary outcomes. In summary, women with celiac disease had a significantly higher risk of the development of obstetric complications that included preterm birth, intrauterine growth restriction, stillbirth, low birthweight, and small for gestational age. Since the treatment with gluten-free diet leads to a significant decrease of preterm delivery, physicians should warn these women about the importance of a strict diet to improve obstetric outcomes. Future studies calculating cost-effectiveness of screening for celiac disease during pregnancy, which could be easily performed, economically and noninvasively, are needed. In addition, further studies are required to determine whether women with adverse pregnancy outcomes should be screened for celiac disease, particularly in countries where the prevalence is high.

Field-wide meta-analyses of observational associations can map selective availability of risk factors and the impact of model specifications

OBJECTIVES

Instead of evaluating one risk factor at a time, we illustrate the utility of "field-wide meta-analyses" in considering all available data on all putative risk factors of a disease simultaneously.

STUDY DESIGN AND SETTING

We identified studies on putative risk factors of pterygium (surfer's eye) in PubMed, EMBASE, and Web of Science. We mapped which factors were considered, reported, and adjusted for in each study. For each putative risk factor, four meta-analyses were done using univariate only, multivariate only, preferentially univariate, or preferentially multivariate estimates.

RESULTS

A total of 2052 records were screened to identify 60 eligible studies reporting on 65 putative risk factors. Only 4 of 60 studies reported both multivariate and univariate regression analyses. None of the 32 studies using multivariate analysis adjusted for the same set of risk factors. Effect sizes from different types of regression analyses led to significantly different summary effect sizes (P-value < 0.001). Observed heterogeneity was very high for both multivariate (median I(2), 76.1%) and univariate (median I(2), 85.8%) estimates. No single study investigated all 11 risk factors that were statistically significant in at least one of our meta-analyses.

CONCLUSION

Field-wide meta-analyses can map availability of risk factors and trends in modeling, adjustments and reporting, as well as the impact of differences in model specification.

Using real-world data to evaluate the association of incretin-based therapies with risk of acute pancreatitis: a meta-analysis of 1,324,515 patients from observational studies

AIM

To investigate the real-world incidence of acute pancreatitis (AP) associated with incretin-based therapy (IBT).

METHODS

We carried out a systematic review and meta-analysis of observational studies using Medline, PubMed, Embase, the Cochrane Database, ClinicalTrials.gov and conference proceedings. We included: those studies in which AP was a pre-defined clinical outcome; longitudinal studies (case-control, cohort); studies that adjusted for confounders; studies that reported on a population exposed to IBT; studies in which non-IBT users or past users (who received IBTs >90 days before the index date) were used as the control group; studies that reported risk estimates [relative risks, odds ratios (ORs) or hazard ratios] with 95% confidence intervals (CIs) for AP event with IBT use, or that reported sufficient data to estimate these; and publications in the English language. Data were extracted by two independent investigators, and a consensus was reached with involvement of a third. Study-specific ORs from seven cohort studies and two case-control studies were meta-analysed using random-effects models. Associations were tested in subgroups representing different patient characteristics and study quality.

RESULTS

A total of nine studies that included 1,324,515 patients and 5195 cases of AP were included in our meta-analysis. The summary estimate of OR for an association between IBT and AP was 1.03 (95% CI 0.87-1.20).

CONCLUSIONS

The present meta-analysis of real-world data does not suggest that IBT is associated with AP. Although we should continue to remain vigilant, IBTs should be regarded as reasonable options to consider adding to the regimen of a patient with type 2 diabetes.

Pubertal timing in girls and depression: a systematic review

BACKGROUND

Because the incidence of depression increases after puberty, it is possible that pubertal timing in girls influences the onset of depression. Our objective was to assess the effect of early and late puberty in girls on the incidence of depression.

METHODS

We systematically searched relevant databases for controlled studies that assessed the impact of pubertal timing in girls on the incidence of depression or depressive symptoms. The last search was completed in August 2013. Two authors selected the studies, extracted the data, and assessed the quality of the evidence. Meta-analyses of the adjusted and unadjusted results were calculated using random effects.

RESULTS

Four cohort studies were included (n=8055 participants). Early puberty significantly increased the risk of new cases of depression in the unadjusted meta-analysis (RR=1.33; CI 95%: 1.02, 1.73) but not in the adjusted estimate of two of the included studies (RR=1.48; CI 95%: 0.69, 2.28). For late puberty, no significant associations were found (unadjusted RR=1.28; CI 95%: 0.87, 1.88). Two studies assessed the effect of early puberty on depressive symptoms and found positive associations. The quality of the available evidence was rated as very low.

LIMITATIONS

The polled results had wide confidence intervals, and the available evidence was of very low quality.

CONCLUSIONS

The available evidence supports little confidence regarding the impact of pubertal timing on the onset of depression in girls but suggests that early puberty in girls may increase the risk of depression. Further higher quality studies are needed to clarify the association between pubertal timing and the incidence of depression in girls and women.

Increasing value and reducing waste: addressing inaccessible research

The methods and results of health research are documented in study protocols, full study reports (detailing all analyses), journal reports, and participant-level datasets. However, protocols, full study reports, and participant-level datasets are rarely available, and journal reports are available for only half of all studies and are plagued by selective reporting of methods and results. Furthermore, information provided in study protocols and reports varies in quality and is often incomplete. When full information about studies is inaccessible, billions of dollars in investment are wasted, bias is introduced, and research and care of patients are detrimentally affected. To help to improve this situation at a systemic level, three main actions are warranted. First, academic institutions and funders should reward investigators who fully disseminate their research protocols, reports, and participant-level datasets. Second, standards for the content of protocols and full study reports and for data sharing practices should be rigorously developed and adopted for all types of health research. Finally, journals, funders, sponsors, research ethics committees, regulators, and legislators should endorse and enforce policies supporting study registration and wide availability of journal reports, full study reports, and participant-level datasets.

The effect of copayments for prescriptions on adherence to prescription medicines in publicly insured populations; a systematic review and meta-analysis

Introduction

Copayments are intended to decrease third party expenditure on pharmaceuticals, particularly those regarded as less essential. However, copayments are associated with decreased use of all medicines. Publicly insured populations encompass some vulnerable patient groups such as older individuals and low income groups, who may be especially susceptible to medication non-adherence when required to pay. Non-adherence has potential consequences of increased morbidity and costs elsewhere in the system.

Objective

To quantify the risk of non-adherence to prescribed medicines in publicly insured populations exposed to copayments.

Methods

The population of interest consisted of cohorts who received public health insurance. The intervention was the introduction of, or an increase, in copayment. The outcome was non-adherence to medications, evaluated using objective measures. Eight electronic databases and the grey literature were systematically searched for relevant articles, along with hand searches of references in review articles and the included studies. Studies were quality appraised using modified EPOC and EHPPH checklists. A random effects model was used to generate the meta-analysis in RevMan v5.1. Statistical heterogeneity was assessed using the I² test; p>0.1 indicated a lack of heterogeneity.

Results

Seven out of 41 studies met the inclusion criteria. Five studies contributed more than 1 result to the meta-analysis. The meta-analysis included 199, 996 people overall; 74, 236 people in the copayment group and 125,760 people in the non-copayment group. Average age was 71.75years. In the copayment group, (verses the non-copayment group), the odds ratio for non-adherence was 1.11 (95% CI 1.09–1.14; P = <0.00001). An acceptable level of heterogeneity at I² = 7%, (p = 0.37) was observed.

Conclusion

This meta-analysis showed an 11% increased odds of non-adherence to medicines in publicly insured populations where copayments for medicines are necessary. Policy-makers should be wary of potential negative clinical outcomes resulting from non-adherence, and also possible knock-on economic repercussions.

Quantitative assessment of the effects of MMP-2 polymorphisms on lung carcinoma risk

BACKGROUND

Previous studies assessing associations between matrix metalloproteinase 2 (MMP-2) polymorphisms and lung cancer risk reported conflicting results. A meta-analysis was therefore performed to derive a more precise estimation.

METHOD

Case-control studies assessing associations between MMP-2 C735T and C1306T polymorphisms and lung cancer risk were included. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were estimated.

RESULTS

7 studies with a total of 3,189 lung cancer cases and 3,013 controls were finally included into this meta-analysis. Overall, the MMP-2 C735T polymorphism was associated with lung cancer risk under the homozygote model (CC versus TT: OR =1.44, 95% CI = 1.03-2.02, I2 = 0%), while the MMP- 2 C1306T polymorphism also associated demonstrated links with all four models (all P values less than 0.05). Subgroup analyses by race suggested obvious associations between MMP-2 C735T and C1306T polymorphisms and lung cancer risk in Asians but not in Caucasians. There was no evidence for publication bias.

CONCLUSION

Currently available evidence supports teh conclusion that MMP-2 C735T and C1306T polymorphisms influence susceptibility to lung cancer in Asians.

Systematic review of HIV transmission between heterosexual serodiscordant couples where the HIV-positive partner is fully suppressed on antiretroviral therapy

BACKGROUND

The risk of sexual HIV transmission in serodiscordant couples when the HIV-positive partner has full virologic suppression on combination antiretroviral therapy (cART) is debated. This study aims to systematically review observational studies and randomized controlled trials (RCTs), evaluating rates of sexual HIV transmission between heterosexual serodiscordant couples when the HIV-positive partner has full suppression on cART.

METHODS AND FINDINGS

We searched major bibliographic databases to November 2012 for relevant observational studies and RCTs without language restrictions. Conference proceedings, key journals and bibliographies were also searched. Studies reporting HIV transmission rates, cART histories and viral loads of the HIV-positive partners were included. Two reviewers extracted methodologic characteristics and outcomes. Of 20,252 citations, 3 studies met all eligibility criteria with confirmed full virologic suppression in the HIV-positive partner. We included 3 additional studies (2 cohort studies, 1 RCT) that did not confirm viral suppression in the HIV-positive partner at transmission in a secondary meta-analysis. Methodologic quality was reasonable. The rate of transmission in the 3 studies confirming virologic suppression was 0 per 100 person-years (95% CI = 0-0.05), with low heterogeneity (I(2) = 0%). When we included the 3 studies that did not confirm virologic suppression, the rate of transmission was 0.14 per 100 person-years (95%CI = 0.04-0.31) (I(2) = 0%). In a sensitivity analysis including all 6 studies, the rate of transmission was 0 per 100 person-years (95%CI = 0-0.01) after omitting all transmissions with known detectable or unconfirmed viral loads, as full suppression in these cases was unlikely. Limitations included lack of data on same-sex couples, type of sexual intercourse (vaginal vs. anal), direction of HIV transmission, exact viral load at the time of transmission, sexually transmitted infections (STI) rates, and extent of condom use.

CONCLUSIONS

Our findings suggest minimal risk of sexual HIV transmission for heterosexual serodiscordant couples when the HIV-positive partner has full viral suppression on cART with caveats regarding information on sexual intercourse type, STIs, and condom use. These findings have implications when counseling heterosexual serodiscordant couples on sexual and reproductive health. More research is needed to explore HIV transmission risk between same-sex couples.

Lack of association between CYP1A1 T6235C polymorphism and coronary artery disease: evidence from a meta-analysis

A number of studies have evaluated the correlation between the cytochrome P450 1A1 (CYP1A1) T6235C polymorphism and coronary artery disease (CAD) risk, however, at present the results remain inconclusive. To provide a more robust investigation of this correlation, a meta-analysis was performed. In the present study, a systematic search of PubMed, Embase and CBM databases for studies published prior to June 6, 2012 was performed. The correlation between the CYP1A1 T6235C polymorphism and CAD risk was assessed by calculating pooled odds ratios (ORs) and 95% confidence intervals (95% CIs). Seven studies with a total of 2,903 cases and 2,304 controls were included in the meta-analysis. Overall, the CYP1A1 T6235C polymorphism was not correlated with CAD risk (C vs. T: OR=1.03; 95% CI, 0.87-1.22; P=0.728; CC vs. TT: OR=1.04; 95% CI, 0.84‑1.19; P=0.699; CC+TC vs. TT: OR=1.04; 95% CI, 0.93-1.18; P=0.478; CC vs. TC+TT: OR=1.04; 95% CI, 0.85‑1.28; P=0.704). A meta-analysis of five high-quality studies demonstrated that the CYP1A1 T6235C polymorphism is not correlated with risk of CAD in 4 genetic models. Ethnic subgroup analyses identified no significant correlation in Caucasian, Asian and African populations. The present meta-analysis study indicates that the CYP1A1 T6235C polymorphism is not correlated with CAD risk. Additional studies with a larger sample size and consistent design must be performed to confirm the present hypothesis.

Quantitative assessment of the association between MTHFR C677T polymorphism and hemorrhagic stroke risk

Many studies have investigated the association between methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism and hemorrhagic stroke, but the impact of MTHFR C677T on hemorrhagic stroke is unclear owing to the obvious inconsistence among those studies. This study aimed to quantify the strength of the association between MTHFR C677T polymorphism and hemorrhagic stroke risk. We searched Pubmed, Emabse and Wangfang databases for studies investigating the association between MTHFR C677T polymorphism and hemorrhagic stroke risk. We estimated the pooled odds ratio (OR) with its 95 % confidence intervals (95 % CI) to assess this possible association. Meta-analysis of included studies suggested that TT genotype was obviously associated with increased risk of hemorrhagic stroke (OR (TT versus CC) = 1.84, 95 % CI 1.45-2.34; OR (TT versus CT) = 1.53, 95 % CI 1.23-1.90; OR (TT versus CT/CC) = 1.64, 95 % CI 1.24-2.00) compared with CC or CT genotypes of MTHFR C677T polymorphism. Subgroup analyses by ethnicity further identified the association above in both Asians and Caucasians. No evidence of publication bias was observed. Thus, meta-analyses of available data suggest an obvious association between MTHFR C677T polymorphism and hemorrhagic stroke risk, and TT genotype contributes to increased risk of hemorrhagic stroke.

Polymorphism of 8q24 rsl3281615 and breast cancer risk : a meta-analysis

Several genome-wide association studies on breast cancer have reported similar findings of a new cancer susceptibility locus, 8q24 rsl3281615. Subsequent case-control studies have rapidly investigated the association between the single nucleotide polymorphism of rsl3281615 at chromosome 8q24 and breast cancer risk, but the effect of 8q24 rsl3281615 polymorphism on breast cancer is still unclear due to the inconsistence among those studies. Given the contradictory findings, a meta-analysis was performed to determine the association between 8q24 rsl3281615 polymorphism and breast cancer risk. 12 eligible case-control studies with a total of 42,508 cases and 53,928 controls were finally included into this meta-analysis by searching the PubMed, Embase, and China Biology Medicine (CBM) databases. We estimated the summary odds ratio (OR) with its corresponding 95 % confidence interval (95 % CI) to assess this association. Meta-analyses of total 12 studies showed 8q24 rsl3281615 polymorphism was significantly associated with an increased risk of breast cancer in all contrast models (OR(G vs. A) = 1.10, 95 % CI 1.05-1.14, P (OR) < 0.001; OR(GG vs. AA) = 1.20, 95 % CI 1.11-1.29, P (OR) < 0.001; OR(AG vs. AA) = 1.08, 95 % CI 1.05-1.12, P (OR) < 0.001; OR(GG vs. AA +AG) = 1.13, 95 % CI 1.07-1.19, P (OR) < 0.001; OR(GG+AG vs. AA) = 1.13, 95 % CI 1.07-1.19, P (OR) < 0.001). Meta-analyses of studies with high quality showed that 8q24 rsl3281615 polymorphism was still significantly associated with an increased risk of breast cancer under the five genetic contrast models. Sensitivity analyses by sequential omission of any individual studies and subgroup analyses by ethnicity further identified the significant association between 8q24 rsl3281615 polymorphism and breast cancer risk. Conclusively, this meta-analysis shows a significant association between 8q24 rsl3281615 polymorphism and breast cancer risk.

CNODES: the Canadian Network for Observational Drug Effect Studies

Although administrative health care databases have long been used to evaluate adverse drug effects, responses to drug safety signals have been slow and uncoordinated. We describe the establishment of the Canadian Network for Observational Drug Effect Studies (CNODES), a collaborating centre of the Drug Safety and Effectiveness Network (DSEN). CNODES is a distributed network of investigators and linked databases in British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, Quebec and Nova Scotia. Principles of operation are as follows: (1) research questions are prioritized by the coordinating office of DSEN; (2) the linked data stay within the provinces; (3) for each question, a study team formulates a detailed protocol enabling consistent analyses in each province; (4) analyses are "blind" to results obtained elsewhere; (5) protocol deviations are permitted for technical reasons only; (6) analyses using multivariable methods are lodged centrally with a methods team, which is responsible for combining the results to provide a summary estimate of effect. These procedures are designed to achieve high internal validity of risk estimates and to eliminate the possibility of selective reporting of analyses or outcomes. The value of a coordinated multi-provincial approach is illustrated by projects studying acute renal injury with high-potency statins, community-acquired pneumonia with proton pump inhibitors, and hyperglycemic emergencies with antipsychotic drugs. CNODES is an academically based distributed network of Canadian researchers and data centres with a commitment to rapid and sophisticated analysis of emerging drug safety signals in study populations totalling over 40 million.

MMP1-1607 1G/2G polymorphism and lung cancer risk: a meta-analysis

Matrix metalloproteinase-1 (MMP-1) plays an important role in the breakdown of extracellular matrix and mediates pathways of apoptosis, angiogenesis, and immunity. It has been demonstrated that MMP-1 overexpression is associated with tumor initiation, invasion, and metastasis. Many studies have investigated the association between MMP1-1607 1G/2G polymorphism and lung cancer risk, but the impact of MMP1-1607 1G/2G polymorphism on lung cancer is unclear owing to the obvious inconsistence among those studies. This study aimed to quantify the strength of the association between MMP1-1607 1G/2G polymorphism and lung cancer risk. We searched the PubMed, Embase, and Wanfang databases for studies on the association between MMP1-1607 1G/2G polymorphism and risk of lung cancer. We estimated summary odds ratio (OR) with its corresponding 95 % confidence interval (95%CI) to assess the association. Overall, MMP1-1607 1G/2G polymorphism was associated with increased risk of lung cancer under four genetic models (OR(2G versus 1G) = 1.21, 95 %CI 1.06-1.37; OR(2G2G versus 1G1G) = 1.36, 95%CI 1.09-1.70; OR(2G2G versus 2G1G+1G1G) = 1.33, 95 %CI 1.10-1.61; and OR(2G2G+2G1G versus 1G1G) = 1.15, 95 %CI 1.04-1.27). Meta-analyses of studies with high quality showed that MMP1-1607 1G/2G polymorphism was still associated with lung cancer risk under those four genetic models. Subgroup analyses by ethnicity and sensitivity analyses further identified the significant association in East Asians. No evidence of publication bias was observed. Meta-analyses of available data show a significant association between MMP1-1607 1G/2G polymorphism and lung cancer risk.

Biracial couples and adverse birth outcomes: a systematic review and meta-analyses

BACKGROUND

Differences in birth outcomes such as low birthweight (LBW), preterm births (PTB), stillbirth, differences in birthweight in Black vs. White race are well known. Infants born to biracial parents (mother and father from either Black or White races) also experience higher adverse birth outcomes.

OBJECTIVE

To systematically review and meta-analyze birth outcomes among parents of mixed racial background compared to parents of same race.

SEARCH STRATEGY

Medline, Embase, CINAHL and bibliographies of identified articles were searched for English language studies.

SELECTION CRITERIA

Studies reporting association between parental mixed racial status and LBW, PTB, or small-for-gestational age (SGA) outcomes were included. DATA COLLECTION AND ANALYSES: After exclusion of duplicate cohorts in different publications, data from White mother-Black father (WMBF), Black mother-White father (BMWF) and Black mother-Black father (BMBF) groups were compared with the White mother-White father (WMWF) group.

RESULTS

Eight English language studies from of 26 335 596 singleton births were included and reviewed. Compared to the WMWF group, the adjusted odds ratio (95% confidence intervals) were: (a) low birthweight; 1.21 (1.10-1.33) for WMBF, 1.75(1.64-1.87) for BMWF, and 2.08 (1.81-2.38) for BMBF; (b) preterm births; 1.17 (1.05-1.31) for WMBF, 1.37 (1.18-1.59) for BMWF, and 1.78 (1.59-2.00) for BMBF; and (c) stillbirths; 1.43 (0.92-2.21) for WMBF, 1.51 (1.09-2.08) for BMWF, and 1.85 (1.47-2.32) for BMBF.

CONCLUSION

Biracial status of parents was associated with higher risk for adverse pregnancy outcomes than both White parents but lower than both Black parents, with maternal race having a greater influence than paternal race on pregnancy outcomes.

Reporting recommendations for tumor marker prognostic studies (REMARK): explanation and elaboration

BACKGROUND

The Reporting Recommendations for Tumor Marker Prognostic Studies (REMARK) checklist consists of 20 items to report for published tumor marker prognostic studies. It was developed to address widespread deficiencies in the reporting of such studies. In this paper we expand on the REMARK checklist to enhance its use and effectiveness through better understanding of the intent of each item and why the information is important to report.

METHODS

REMARK recommends including a transparent and full description of research goals and hypotheses, subject selection, specimen and assay considerations, marker measurement methods, statistical design and analysis, and study results. Each checklist item is explained and accompanied by published examples of good reporting, and relevant empirical evidence of the quality of reporting. We give prominence to discussion of the 'REMARK profile', a suggested tabular format for summarizing key study details.

SUMMARY

The paper provides a comprehensive overview to educate on good reporting and provide a valuable reference for the many issues to consider when designing, conducting, and analyzing tumor marker studies and prognostic studies in medicine in general. To encourage dissemination of the Reporting Recommendations for Tumor Marker Prognostic Studies (REMARK): Explanation and Elaboration, this article has also been published in PLoS Medicine.

Cyclin D1 G870A polymorphism and lung cancer risk: a meta-analysis

Many studies have investigated the association between Cyclin D1 (CCND1) G870A polymorphism and lung cancer risk, but the impact of CCND G870A polymorphism on lung cancer is unclear owing to the obvious inconsistence among those studies. This study aimed to quantify the strength of association between CCND1 G870A polymorphism and lung cancer risk. We searched the PubMed, Embase, and Wangfang databases for articles on studies relating the CCND1 G870A polymorphism to the risk of lung cancer in humans. We estimated summary odds ratios (ORs) with their confidence intervals (CIs) to assess the association. Meta-analyses of total studies showed that CCND1 G870A polymorphism was associated with lung cancer risk under three genetic models (OR(A versus G) = 1.13, 95 % CI 1.03-1.24; OR(AA versus GG) = 1.20, 95 % CI 1.07-1.35; OR(AA versus AG + GG) = 1.23, 95 % CI 1.02-1.50). Meta-analyses of studies with high quality showed that CCND1 G870A polymorphism was associated with lung cancer risk under two genetic models (OR(A versus G) = 1.08, 95 % CI 1.02-1.15; OR(AA versus GG) = 1.17, 95 % CI 1.04-1.32). Subgroup analyses by ethnicity and sensitivity analyses further identified the significant association above. No evidence of publication bias was observed. Meta-analyses of available data show a significant association between the CCND1 G870A polymorphism and lung cancer risk, and CCND1 G870A polymorphic variant A contributes to increased risk of lung cancer.

Risk of hip fracture with hip or knee osteoarthritis: a systematic review

Osteoarthritis (OA) and hip fracture are two common musculoskeletal disorders associated with substantial societal and personal burden. The objective of this systematic review was to determine the association between hip or knee OA and risk of hip fractures in people aged 45 years and older as compared to people aged 45 years and older who do not have OA. We searched CINAHL, Cochrane Database of Systematic Reviews, Embase, OVID Medline, PUBMED, and SCOPUS for studies published up to July 2010 and conducted forward searches of included studies using Web of Science. Two reviewers independently screened articles for inclusion, extracted data, and evaluated the risk of bias of included studies using the Newcastle-Ottawa Scale. Eleven articles were included. Three investigated individuals with knee OA, two included adults with knee or hip OA, and six investigated adults with hip OA. We did not combine the hip OA or the knee OA studies in a meta-analysis due to the heterogeneity in: study populations and covariates adjusted for in estimates of association. Hip OA may be related to a decreased risk of hip fracture when considering crude estimates of association or estimates of association adjusted for a limited number of covariates, although not all studies found support for the presence of this association. The association between knee OA and hip fracture remains unclear. The presence of OA in the hip or knee should not act as an indication that assessment for hip fracture risk is unnecessary.

Maternal marital status and birth outcomes: a systematic review and meta-analyses

Systematically review risks of an infant being born with low birth weight (LBW), preterm birth (PTB) or small for gestational age (SGA) among married and unmarried women. Medline, Embase, CINAHL, and bibliographies of identified articles were searched for English language studies. Studies reporting birth outcomes of married and unmarried (single and cohabitant) were included. Two reviewers independently collected data and assessed the quality of the studies for biases in sample selection, exposure assessment, confounder, analytical, outcome assessments, and attrition. Meta-analyses were performed using random effect model for both unadjusted and adjusted data and odds ratio (OR), and 95% confidence interval (CI) were calculated. Twenty-one studies of low to moderate risk of bias were included. Compared to married mothers unadjusted odds of (a) LBW was increased among unmarried (OR 1.46, 95%CI 1.25-1.71), single (OR 1.65, 95%CI 1.44-1.88) and cohabitating (OR 1.29, 95%CI 1.25-1.32) mothers; (b) PTB was increased among unmarried (OR 1.22, 95%CI 1.14-1.31), single (OR 1.54, 95%CI 1.39-1.72) and cohabitating (OR 1.15, 95%CI 1.08-1.23) mothers and (c) SGA birth was increased among unmarried (OR 1.45, 95%CI 1.32-1.61), single (OR 1.70, 95%CI 1.47-1.97) and cohabitating (OR 1.36, 95%CI 1.30-1.42) mothers. Meta-analyses of adjusted odds estimates confirmed these findings at marginally lower odds. Maternal unmarried status is associated with an increased risk of LBW, PTB and SGA births.

Reporting Recommendations for Tumor Marker Prognostic Studies (REMARK): explanation and elaboration

The REMARK (Reporting Recommendations for Tumor Marker Prognostic Studies) guideline includes a checklist which aims to improve the reporting of these types of studies. Here, we expand on the REMARK checklist to enhance its use and effectiveness through better understanding of the intent of each item and why the information is important to report. Each checklist item of the REMARK guideline is explained in detail and accompanied by published examples of good reporting. The paper provides a comprehensive overview to educate on good reporting and provide a valuable reference of issues to consider when designing, conducting, and analyzing tumor marker studies and prognostic studies in medicine in general.

Reporting on covariate adjustment in randomised controlled trials before and after revision of the 2001 CONSORT statement: a literature review

OBJECTIVES

To evaluate the use and reporting of adjusted analysis in randomised controlled trials (RCTs) and compare the quality of reporting before and after the revision of the CONSORT Statement in 2001.

DESIGN

Comparison of two cross sectional samples of published articles.

DATA SOURCES

Journal articles indexed on PubMed in December 2000 and December 2006.

STUDY SELECTION

Parallel group RCTs with a full publication carried out in humans and published in English

MAIN OUTCOME MEASURES

Proportion of articles reported adjusted analysis; use of adjusted analysis; the reason for adjustment; the method of adjustment and the reporting of adjusted analysis results in the main text and abstract.

RESULTS

In both cohorts, 25% of studies reported adjusted analysis (84/355 in 2000 vs 113/422 in 2006). Compared with articles reporting only unadjusted analyses, articles that reported adjusted analyses were more likely to specify primary outcomes, involve multiple centers, perform stratified randomization, be published in general medical journals, and recruit larger sample sizes. In both years a minority of articles explained why and how covariates were selected for adjustment (20% to 30%). Almost all articles specified the statistical methods used for adjustment (99% in 2000 vs 100% in 2006) but only 5% and 10%, respectively, reported both adjusted and unadjusted results as recommended in the CONSORT guidelines.

CONCLUSION

There was no evidence of change in the reporting of adjusted analysis results five years after the revision of the CONSORT Statement and only a few articles adhered fully to the CONSORT recommendations.

Preterm birth and low birth weight among in vitro fertilization twins: a systematic review and meta-analyses

OBJECTIVE

The objective of this systematic review and meta-analyses was to determine the risks of preterm birth (PTB) and low birth weight (LBW) in twins conceived through in vitro fertilization (IVF) or IVF/intracytoplasmic sperm injection (ICSI) compared to spontaneously-conceived twins after matching or controlling for at least maternal age.

STUDY DESIGN

The MOOSE guidelines for meta-analysis of observational studies were followed.

SEARCH STRATEGY

Medline and Embase were searched using comprehensive search strategies. Bibliographies of identified articles were reviewed.

SELECTION CRITERIA

English language studies of twins conceived by IVF or IVF/ICSI, compared with spontaneously twins, that matched or controlled for at least maternal age.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed titles, abstracts, articles and study quality and extracted data. Statistical analyses were performed using the Review Manager (RevMan 5.0) software using a random effects model. Dichotomous data were meta-analyzed using relative risks (RR) and continuous data with a weighted mean difference.

RESULTS

Twelve studies were included which had a total of 4385 twins conceived after IVF or IVF/ICSI (one stillbirth was excluded) and 11,793 spontaneously-conceived twins. After matching or controlling for maternal age and often other factors, compared to spontaneously-conceived twins, IVF twins had increased risks of both our primary outcomes: PTB (RR 1.23, 95% CI 1.09, 1.41) and LBW (<2500 g, RR 1.14, 95% CI 1.06, 1.22). They were at increased risk for PTB <32-33 weeks (RR 1.63, 95% CI 1.17, 2.27) although the risks of late PTB (32-36 weeks, RR 1.12, 95% CI 0.85, 1.47), very LBW (<1500 g, RR 1.28, 95% CI 0.73, 2.24), extremely LBW (<1000 g, RR 0.88, 0.04, 19.40), intrauterine growth restriction (RR 1.06, 95% CI 0.72, 1.55) and the difference in the duration of gestation (-0.5 weeks, 95% CI -1.2 weeks, 0.2 weeks) were not statistically significantly increased compared to spontaneously-conceived twins. IVF twins had significantly lower mean birth weights (-105 g, 95% CI -204 g, -3 g).

CONCLUSIONS

IVF twins have small but significantly increased risks of PTB, LBW, and lower mean birth weight compared to spontaneously-conceived twins after matching or controlling for at least maternal age.