Hidden biases in observational epidemiology: the case of unmeasured confounding

Randomized controlled trials: not always the "gold standard" for evidence in obstetrics and gynecology

Randomized controlled trials are considered the "gold standard" for therapeutic interventions, and it is not uncommon for sweeping changes in medical practice to follow positive results from such trials. However, randomized controlled trials are not without their limitations. Physicians frequently view randomized controlled trials as infallible, whereas they tend to dismiss evidence derived from sources other than randomized controlled trials as less credible or reliable. In several situations in obstetrics and gynecology, there are no randomized controlled trials to help guide the clinician. In these circumstances, it is important to evaluate the entire body of evidence including observational studies, rather than dismiss interventions altogether simply because no randomized controlled trials exist. Randomized controlled trials and observational studies should be viewed as complementary rather than at odds with each other. Some reversals in widely adopted clinical practice have recently been implemented following subsequent studies that contradicted the outcomes of major randomized controlled trials. The most notable of these was the withdrawal from the market of 17-hydroxyprogesterone caproate for preterm birth prevention. Such reversals could potentially have been averted if the inherent limitations of randomized controlled trials were carefully considered before implementing these universal practice changes. This Clinical Opinion underscores the limitations of an exclusive reliance on randomized controlled trials while disregarding other evidence in determining how best to care for patients. Solutions are proposed that advocate that clinicians adopt a more balanced perspective that considers the entirety of the available medical evidence and the individual patient characteristics, needs, and wishes.

Association between urate-lowering therapy and cardiovascular events in patients with asymptomatic hyperuricemia

INTRODUCTION/OBJECTIVES

To investigate the role of urate-lowering therapy (ULT) in the prevention of cardiovascular disease (CVD) in patients with asymptomatic hyperuricemia using the Japanese healthcare record database.

METHODS

This retrospective cohort study used data from the JMDC Claims Database, which includes records of medical check-ups and Japanese health insurance claims. Subjects aged at least 18 years with a serum uric acid (sUA) level ≥ 7.0 mg/dL and at least one medical check-up from January 2007 to August 2021 were included in this study. The exposure was any ULT prescription, and the primary outcome included composite CVD outcomes, including coronary artery disease, stroke, and atrial fibrillation. Analysis was performed with a new-user design and overlap weighting to balance the baseline characteristics of the subjects. Cox proportional hazards models were used to investigate the association between ULT and the development of CVD.

RESULTS

In total, 152,166 patients were included in the main analysis before overlap weighting in this retrospective cohort study. The number of subjects in the ULT group was 5,270, and there were 146,896 subjects in the control group. Composite CVD outcomes were observed in a total of 7,703 patients. The risk of developing composite CVD outcomes was not different between the ULT group and the control group (HR: 1.01, 95% CI: 0.89 to 1.13).

CONCLUSIONS

ULT for patients with asymptomatic hyperuricemia did not prevent the development of CVD based on the Japanese claims database. Key points • Among subjects with asymptomatic hyperuricemia, ULT was not associated with a lower risk of CVD • There was no appropriate cutoff for initiating ULT in patients with asymptomatic hyperuricemia • There was no appropriate cutoff as the therapeutic goal of ULT in patients with asymptomatic hyperuricemia.

Association between smoking status and inpatient outcomes of acute cholangitis in the United States: a propensity matched analysis

Background

Acute cholangitis (AC) is an infection of the biliary tract superimposed on stasis. This study aimed to investigate the effects of smoking on inpatient outcomes of AC.

Methods

We identified primary AC hospitalizations using the National Inpatient Sample database (2017-2020). Using a 1:1 matching method, we created a matched comparison cohort of AC patients who were non-smokers, based on demographics, hospital characteristics and comorbidities.

Results

We matched 3960 smoker patients with 3960 non-smoker patients within the AC population. Non-smokers were older than smokers (70 vs. 59 years, P<0.001). Smokers had a stronger association with bile duct calculi (74.37% vs. 69.29%, P<0.001) and other bile duct disorders (clots, parasites, extrinsic compression and other rare disorders) (6.82% vs. 5.05%, P=0.011). No significant difference in inpatient mortality, median length of stay (LOS), or median inpatient cost (MIC) was found between the matched cohorts (P>0.05). However, smoking was associated with higher odds of complications, including sepsis without shock (0.88% vs. 0.51%, P=0.042), sepsis with shock (1.26% vs. 0.51%, P<0.001), biliary pancreatitis (6.57% vs. 4.42%, P<0.001) and myocardial infarction (6.19% vs. 3.54%, P<0.001), as well as a greater need for inpatient endoscopic retrograde cholangiopancreatography (ERCP) (72.85% vs. 63.76%, P<0.001) and early ERCP (50.76% vs. 42.32%, P<0.001) compared to non-smokers.

Conclusions

This study found no difference in mortality, LOS, or MIC in acute cholangitis-related hospitalizations associated with smoking. However, smoking was associated with a higher risk of complications and a greater need for ERCP and early ERCP.

Leveraging electronic health record data for endometriosis research

Endometriosis is a chronic, complex disease for which there are vast disparities in diagnosis and treatment between sociodemographic groups. Clinical presentation of endometriosis can vary from asymptomatic disease-often identified during (in)fertility consultations-to dysmenorrhea and debilitating pelvic pain. Because of this complexity, delayed diagnosis (mean time to diagnosis is 1.7-3.6 years) and misdiagnosis is common. Early and accurate diagnosis of endometriosis remains a research priority for patient advocates and healthcare providers. Electronic health records (EHRs) have been widely adopted as a data source in biomedical research. However, they remain a largely untapped source of data for endometriosis research. EHRs capture diverse, real-world patient populations and care trajectories and can be used to learn patterns of underlying risk factors for endometriosis which, in turn, can be used to inform screening guidelines to help clinicians efficiently and effectively recognize and diagnose the disease in all patient populations reducing inequities in care. Here, we provide an overview of the advantages and limitations of using EHR data to study endometriosis. We describe the prevalence of endometriosis observed in diverse populations from multiple healthcare institutions, examples of variables that can be extracted from EHRs to enhance the accuracy of endometriosis prediction, and opportunities to leverage longitudinal EHR data to improve our understanding of long-term health consequences for all patients.

The Global Pregnancy Collaboration (CoLab) symposium on short- and long-term outcomes in offspring whose mothers had preeclampsia: A scoping review of clinical evidence

Preeclampsia is a maternal syndrome characterized by the new onset of hypertension after 20 weeks of gestation associated with multisystemic complications leading to high maternal and fetal/neonatal morbidity and mortality. However, sequelae of preeclampsia may extend years after pregnancy in both mothers and their children. In addition to the long-term adverse cardiovascular effects of preeclampsia in the mother, observational studies have reported elevated risk of cardiovascular, metabolic, cerebral and cognitive complications in children born from women with preeclampsia. Less clear is whether the association between maternal preeclampsia and offspring sequelae are causal, or to what degree the associations might be driven by fetal factors including impaired growth and the health of its placenta. Our discussion of these complexities in the 2018 Global Pregnancy Collaboration annual meeting prompted us to write this review. We aimed to summarize the evidence of an association between maternal preeclampsia and neurobehavioral developmental disorders in offspring in hopes of generating greater research interest in this important topic.

Endothelial Dysfunction in Patients with Advanced Heart Failure Treated with Levosimendan Periodic Infusion Compared with Optimal Medical Therapy: A Pilot Study

Endothelial dysfunction (ED) is frequently found in patients with heart failure (HF). Among several pharmacological agents reported to improve endothelial function, levosimendan seems to be a promising one, even though, to date, only two previously published studies have evaluated its effects on ED in these patients. The aim of our pilot study was to further investigate the role of periodic levosimendan infusion on endothelial function in patients affected by advanced HF. In this cross-sectional study, three different groups were enrolled: 20 patients with advanced HF treated with periodic levosimendan (LEVO), 20 patients with HF on optimal medical therapy (OMT), and 20 healthy subjects (control group). ED was evaluated through flow-mediated dilation (FMD) at the level of the brachial artery. The three groups presented similar ages with significant differences in gender distribution, systolic blood pressure, and chronic kidney disease (eGFR < 30 mL/min). In HF patients, ischaemic aetiology was more prevalent in the LEVO group than in the OMT group (60 vs. 40%, p < 0.001). The New York Heart Association (NYHA) functional class was worse in the LEVO group, as well as in NT-proBNP (5636.7 ± 6164.6 ng/dL and 1243.7 ± 1487.2 ng/dL, in the LEVO and OMT groups, respectively, p = 0.005). The FMD was significantly higher in the healthy control group compared to that of the OMT group (15.7 ± 6.4 vs. 9.1 ± 6.0%, p = 0.007) while it showed an intermediate value in LEVO patients (12.4 ± 7.1%) (ANOVA p = 0.010). In conclusion, levosimendan therapy seems to ameliorate endothelial dysfunction related to heart failure. Longitudinal studies in patients on periodic therapy are needed in order to confirm the long-term effects of levosimendan on ED.

Risk of large for gestational age births at early, full and late term in relation to pre-pregnancy body mass index: Mediation by gestational diabetes status

BACKGROUND

Maternal pre-pregnancy body mass index (BMI) is strongly associated with infant birthweight and the risk differs in pregnancies complicated by gestational diabetes (GDM).

OBJECTIVES

To examine the risk of large for gestational age (LGA) (≥97th percentile) singleton births at early term, full term and late term in relation to maternal pre-pregnancy BMI status mediated through GDM.

METHODS

We analysed data from the 2018 U.S. National Vital Statistics Natality File restricted to singleton term births (N = 3,229,783). In counterfactual models for causal inference, we estimated the total effect (TE), natural direct effect (NDE) and natural indirect effect (NIE) for the association of pre-pregnancy BMI with subcategories of LGA births at early, full and late term mediated through GDM, using log-binomial regression and adjusting for race/ethnicity, age, education, parity and infant sex. Proportion mediated was calculated on the risk difference scale and potential unmeasured confounders were assessed using the E-value.

RESULTS

Overall, 6.4% of women had GDM, and there were 3.6% LGA singleton term births. The highest prevalence of GDM was among pre-gestational overweight/obesity that also had the highest rates of LGA births at term. The TE estimates for the risk of LGA births were the strongest across women with higher pre-pregnancy BMI compared to women with normal pre-pregnancy BMI. The NDE estimates were higher than the NIE estimates for overweight/obese BMI status. The proportion mediated, which answers the causal question to what extent the total effect of the association between pre-pregnancy BMI and LGA births is accounted for through GDM, was the highest (up to 16%) for early term births.

CONCLUSIONS

Term singleton births make up the largest proportion in a cohort of newborns. While the percentage mediated through GDM was relatively small, health risks arising from pre-pregnancy overweight, and obesity can be substantial to both mothers and their offspring.

A principled approach to mediation analysis in perinatal epidemiology

For many research questions in perinatal epidemiology, gestational age is a mediator that features the causal pathway between exposure and outcome. A mediator is an intermediate variable between an exposure and outcome, which is influenced by the exposure on the causal pathway to the outcome. Therefore, conventional analyses that adjust, stratify, or match for gestational age or its proxy (eg, preterm vs term deliveries) are problematic. This practice, which is entrenched in perinatal research, induces an overadjustment bias. Depending on the causal question, it may be inappropriate to adjust (or condition) for a mediator, such as gestational age, by either design or statistical analysis, but its effect can be quantified through causal mediation analysis. In an exposition of such methods, we demonstrated the relationship between the exposure and outcome and provided a formal analytical framework to quantify the extent to which a causal effect is influenced by a mediator. We reviewed concepts of confounding and causal inference, introduced the concept of a mediator and illustrated the perils of adjusting for a mediator in an exposure-outcome paradigm for a given causal question, adopted causal methods that call for an evaluation of a mediator in a causal exposure effect on the outcome, and discussed unmeasured confounding assumptions in mediation analysis. Furthermore, we reviewed other developments in the causal mediation analysis literature, including decomposition of a total effect when the mediator interacts with the exposure (4-way decomposition), methods for multiple mediators, mediation methods for case-control studies, mediation methods for time-to-event outcomes, sample size and power analysis for mediation analysis, and available software to apply these methods. To illustrate these methods, we provided a clinical example to estimate the risk of perinatal mortality (outcome) concerning placental abruption (exposure) and to determine the extent to which preterm delivery (mediator; a proxy for gestational age) plays a role in this causal effect. We hoped that the adoption of mediation methods described in this review will move research in perinatal epidemiology away from biased adjustments of mediators toward a more nuanced quantification of effects that pose unique challenges and provide unique insights in our field.

Perinatal and Child Factors Mediate the Association between Preeclampsia and Offspring School Performance

OBJECTIVE

To determine whether maternal preeclampsia is an independent risk factor for poorer academic school performance in offspring, taking into account important perinatal and child factors.

STUDY DESIGN

A population-based cohort study using record-linkage of state-wide data was undertaken. We evaluated children born at 28+ weeks of gestation in New South Wales, Australia who had grade 3 record-linked education outcomes via the National Assessment Program-Literacy and Numeracy (NAPLAN) between 2009 and 2014. Children with in utero preeclampsia exposure were compared with those without exposure. Robust multivariable Poisson models were used to determine adjusted relative risks.

RESULTS

Crude models demonstrated an increased risk of scoring below the national minimal standard in all 5 domains (reading, writing, spelling, grammar and punctuation, and numeracy) for children exposed to preeclampsia, ranging from a relative risk (RR) of 1.13 (95% CI, 1.04-1.24) for reading to 1.19 (95% CI, 1.09-1.30) for numeracy. These differences were attenuated once adjusted for perinatal and child factors (RR, 1.07 [95% CI, 0.97-1.18] to 1.11 (95% CI, 0.99-1.22]), with combined perinatal and childhood factors mediating between 35.7% (writing) to 55.1% (spelling) of the association. Gestational age at birth was the most important perinatal factor, explaining 10.5% (grammar and punctuation) to 20.6% (writing) of the association between preeclampsia and poor school performance, followed by small for gestational age.

CONCLUSION

The poorer educational performance experienced by children born to women with preeclampsia appears largely attributable to perinatal and childhood factors, suggesting an opportunity to improve school performance in children exposed to preeclampsia by optimizing these perinatal factors, particularly gestational age at birth.

Resuscitation outcomes for weekend deliveries of very low birthweight infants

OBJECTIVE

To characterise the association between weekend (Saturday and Sunday) deliveries of very low birthweight (VLBW) infants and delivery room outcomes in the 'golden hour' after birth.

DESIGN AND SETTING

A retrospective cohort study using California Perinatal Quality Care Collaborative data from participating neonatal intensive care units.

PATIENTS

The study population after exclusions was 26 515 VLBW infants born in California from 2010 to 2016.

MAIN OUTCOME MEASURES

Delivery room outcomes assessed included: chest compressions, epinephrine, intubation prior to continuous positive airway pressure ventilation, 5 min Apgar <4, admission hypothermia and death within 12 hours. To adjust for potential confounders, we fit multivariate regression models controlling for two sets of infant, maternal and hospital characteristics.

RESULTS

Infants delivered on weekends were less likely to have been prenatally diagnosed with intrauterine growth restriction but were otherwise not significantly different in gestational age, ethnicity, sex or maternal risk factors than those born during weekdays. Caesarean deliveries were less common on weekends, while vaginal deliveries were consistent across all days. After adjusting for sex and race, weekend delivery was associated with delivery room chest compressions (OR: 1.12, 95% CI 1.02 to 1.24) and lower 5 min Apgar (OR: 1.11, 95% CI 1.01 to 1.21).

CONCLUSION

In this population-based study of VLBW infants, there was an increase in chest compressions for infants born on the weekend. More research is needed on the differences between populations born on weekdays versus weekends, and how these may contribute to observed associations.

Causal Model of the Association of Social Support With Antepartum Depression: A Marginal Structural Modeling Approach

We used marginal structural models to evaluate associations of social support with antepartum depression in late pregnancy, if everyone had had high social support both before pregnancy and during early pregnancy, compared with having low social support at one of the 2 time points or low social support at both time points. In 2012-2014, pregnant Peruvian women (n = 3,336) were recruited into a prospective cohort study (at a mean gestational age of 9 weeks). A follow-up interview (n = 2,279) was conducted (at 26-28 weeks of gestation). Number of available support providers and satisfaction with social support were measured using Sarason Social Support Questionnaire-6. Depression was measured using the Edinburgh Postnatal Depression Scale. Low number of support providers at both time points was associated with increased risk of depression (odds ratio = 1.62, 95% confidence interval: 1.12, 2.34). The association for low satisfaction at both time points was marginally significant (odds ratio = 1.41, 95% confidence interval: 0.99, 1.99). Depression risk was not significantly higher for women who reported high social support at one of the 2 time points. Our study reinforces the importance of assessing social support before and during pregnancy and underscores the need for future interventions targeted at increasing the number of support providers to prevent antepartum depression.