Warning of Immortal Time Bias When Studying Drug Safety in Pregnancy: Application to Late Use of Antibiotics and Preterm Delivery

Emulating Target Trials to Avoid Immortal Time Bias - An Application to Antibiotic Initiation and Preterm Delivery

BACKGROUND

Randomized trials in pregnancy are extremely challenging, and observational studies are often the only option to evaluate medication safety during pregnancy. However, such studies are often susceptible to immortal time bias if treatment initiation occurs after time zero of follow-up. We describe how emulating a sequence of target trials avoids immortal time bias and apply the approach to estimate the safety of antibiotic initiation between 24 and 37 weeks gestation on preterm delivery.

METHODS

The Tsepamo Study captured birth outcomes at hospitals throughout Botswana from 2014 to 2021. We emulated 13 sequential target trials of antibiotic initiation versus no initiation among individuals presenting to care <24 weeks, one for each week from 24 to 37 weeks. For each trial, eligible individuals had not previously initiated antibiotics. We also conducted an analysis susceptible to immortal time bias by defining time zero as 24 weeks and exposure as antibiotic initiation between 24 and 37 weeks. We calculated adjusted risk ratios (RR) and 95% confidence intervals (CI) for preterm delivery.

RESULTS

Of 111,403 eligible individuals, 17,009 (15.3%) initiated antibiotics between 24 and 37 weeks. In the sequence of target trials, RRs (95% CIs) ranged from 1.04 (0.90, 1.19) to 1.24 (1.11, 1.39) (pooled RR: 1.11 [1.06, 1.15]). In the analysis susceptible to immortal time bias, the RR was 0.90 (0.86, 0.94).

CONCLUSIONS

Defining exposure as antibiotic initiation at any time during follow-up after time zero resulted in substantial immortal time bias, making antibiotics appear protective against preterm delivery. Conducting a sequence of target trials can avoid immortal time bias in pregnancy studies.

Association Between Residential Proximity to Hydraulic Fracturing Sites and Adverse Birth Outcomes

IMPORTANCE

The association between hydraulic fracturing and human development is not well understood. Several studies have identified significant associations between unconventional natural gas development and adverse birth outcomes; however, geology and legislation vary between regions.

OBJECTIVE

To examine the overall association between residential proximity to hydraulic fracturing sites and adverse birth outcomes, and investigate whether well density influenced this association.

DESIGN, SETTING, AND PARTICIPANTS

This population-based retrospective cohort study of pregnant individuals in rural Alberta, Canada, took place from 2013 to 2018. Participants included reproductive-aged individuals (18-50 years) who had a pregnancy from January 1, 2013, to December 31, 2018, and lived in rural areas. Individuals were excluded if they lived in an urban setting, were outside of the age range, or were missing data on infant sex, postal code, or area-level socioeconomic status.

EXPOSURES

Oil and gas wells that underwent hydraulic fracturing between 2013 to 2018 were identified through the Alberta Energy Regulator (n = 4871). Individuals were considered exposed if their postal delivery point was located within 10 km of 1 or more wells that was hydraulically fractured during 1 year preconception or during pregnancy.

MAIN OUTCOMES AND MEASURES

Outcomes investigated were spontaneous and indicated preterm birth, small for gestational age, major congenital anomalies, and severe neonatal morbidity or mortality.

RESULTS

After exclusions, the sample included 26 193 individuals with 34 873 unique pregnancies, and a mean (SD) parental age of 28.2 (5.2) years. Small for gestational age and major congenital anomalies were significantly higher for individuals who lived within 10 km of at least 1 hydraulically fractured well after adjusting for parental age at delivery, multiple births, fetal sex, obstetric comorbidities, and area-level socioeconomic status. Risk of spontaneous preterm birth and small for gestational age were significantly increased in those with 100 or more wells within 10 km.

CONCLUSIONS AND RELEVANCE

Results suggest that individuals who were exposed to hydraulic fracturing within pregnancy may be at higher risk of several adverse birth outcomes. These results may be relevant to health policy regarding legislation of unconventional oil and gas development in Canada and internationally.

Influenza Vaccination Effectiveness in Paediatric ‘Healthy’ Patients: A Population-Based Study in Italy

Background: Seasonal influenza can cause serious morbidity, mortality, and financial burden in pediatric and adult populations. The influenza vaccine (IV) is considered the most effective way to prevent influenza and influenza-like-illness (ILI) complications. Objective: To assess the effectiveness of the IV in a cohort of healthy children in Italy. Methods: From the Pedianet database, all healthy children aged six months–14 years between 2009–2019 were enrolled. Cox proportional-hazards models were fitted to estimate hazard ratios and the 95% confidence interval for the association between IV exposure during each season of interest (from October to April of each year) with incident influenza/ILI. Exposure was considered as a time-varying variable. Vaccine effectiveness (VE) was calculated as (1-HR) × 100. The additive and prolonged effects of IV were evaluated across the seasons. Results: We found a high IV effectiveness among healthy children. No additional or prolonged effects were found. Conclusion: Our data indicates that IV was effective in preventing influenza/ILI in healthy children. Therefore, IV should be encouraged and provided free of charge to healthy children in all the Italian regions every year, reducing disease spread and lowering the burden on the pediatric population.

Methodological Considerations for Preterm Birth Research

Complications from preterm birth are a leading cause of infant mortality, with long-term implications for morbidity and quality of life of preterm infants. There are many important risk factors for preterm births however in this article, we focus on the maternal infection etiological pathway, given its significance in low-to-middle income countries. In high preterm birth settings such as sub-Saharan Africa, maternal HIV infection and antiretroviral therapy (ART) use have been associated with an increased risk of preterm births. Consequently, we highlight methodological considerations related to selection and measurement bias in preterm birth research. We further illustrate the potential impact of these biases in studies investigating the relationship between HIV/ART and preterm births. We also briefly discuss issues related to population-level estimations based on routinely collected clinical or civil registration data. We conclude by emphasizing the importance of strengthening of antenatal care services to improve quality of population data as well as optimizing current and future study designs, by taking into account the important methodological considerations described in this article.

Use of Antibiotic Treatment in Pregnancy and the Risk of Several Neonatal Outcomes: A Population-Based Study

BACKGROUND

Limited evidence is available on the safety and efficacy of antimicrobials during pregnancy, with even less according to the trimester of their use.

OBJECTIVE

This study aimed to evaluate the association between exposure to antibiotics therapy (AT) during pregnancy and short-term neonatal outcomes.

METHODS

We considered 773,237 deliveries that occurred between 2007-2017 in the Lombardy region of Italy. We evaluated the risk of neonatal outcomes among infants that were born to mothers who underwent AT during pregnancy. The odds ratios and the hazard ratios, with the 95% confidence intervals, were estimated respectively for early (first/second trimester) and late (third trimester) exposure. The propensity score was used to account for potential confounders. We also performed subgroup analysis for the class of AT.

RESULTS

We identified 132,024 and 76,921 singletons that were exposed to AT during early and late pregnancy, respectively. Infants born to mothers with early exposure had 17, 11, and 16% increased risk of preterm birth, low birth weight, and low Apgar score, respectively. Infants that were exposed in late pregnancy had 25, 11, and 13% increased risk of preterm birth, low birth weight, and low Apgar score, respectively. The results were consistent in the subgroup analysis.

CONCLUSION

Our results suggested an increased risk of several neonatal outcomes in women exposed to ATs during pregnancy, albeit we were not able to assess to what extent the observed effects were due to the infection itself. To reduce the risk of neonatal outcomes, women that are prescribed AT during pregnancy should be closely monitored.

Analytical challenges in estimating the effect of exposures that are bounded by follow-up time: experiences from the Blood Stream Infection-Focus on Outcomes study

Objective

To illustrate the challenges of estimating the effect of an exposure that is bounded by duration of follow-up on all-cause 28-day mortality, whilst simultaneously addressing missing data and time-varying covariates.

Study design and methods

BSI-FOO is a multicentre cohort study with the primary aim of quantifying the effect of modifiable risk factors, including time to initiation of therapy, on all-cause 28-day mortality in patients with bloodstream infection. The primary analysis involved two Cox proportional hazard models, first one for non-modifiable risk factors and second one for modifiable risk factors, with a risk score calculated from the first model included as a covariate in the second model. Modifiable risk factors considered in this study were recorded daily for a maximum of 28 days after infection. Follow-up was split at daily intervals from day 0 to 28 with values of daily collected data updated at each interval (i.e., one row per patient per day).

Analytical challenges

Estimating the effect of time to initiation of treatment on survival is analytically challenging since only those who survive to time t can wait until time t to start treatment, introducing immortal time bias. Time-varying covariates representing cumulative counts were used for variables bounded by survival time e.g. the cumulative count of days before first receipt of treatment. Multiple imputation using chained equations was used to impute missing data, using conditional imputation to avoid imputing non-applicable data e.g. ward data after discharge.

Conclusion

Using time-varying covariates represented by cumulative counts within a one row per day per patient framework can reduce the risk of bias in effect estimates. The approach followed uses established methodology and is easily implemented in standard statistical packages.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12874-021-01393-9.

Statistical Advances in Epidemiology and Public Health

The key role of statistical modeling in epidemiology and public health is unquestionable [...].

Association between Adherence with Recommended Antenatal Care in Low-Risk, Uncomplicated Pregnancy, and Maternal and Neonatal Adverse Outcomes: Evidence from Italy

Antenatal care (ANC) aims of monitoring wellbeing of mother and foetus during pregnancy. We validate a set of indicators aimed of measuring the quality of ANC of women on low-risk, uncomplicated pregnancy through their relationship with maternal and neonatal outcomes. We conducted a population-based cohort study including 122,563 deliveries that occurred between 2015 and 2017 in the Lombardy Region, Italy. Promptness and appropriateness of number and timing of gynaecological visits, ultrasounds and laboratory tests were evaluated. We assessed several maternal and neonatal outcomes. Log-binomial regression models were used to estimate prevalence ratio (PR), and corresponding 95% confidence interval (95% CI), for the exposure→outcome association. Compared with women who adhered with recommendations, those who were no adherent had a significant higher prevalence of maternal intensive care units admission (PR: 3.1, 95%CI: 1.2-7.9; and 2.7, 1.1-7.0 respectively for promptness of gynaecological visits, and appropriateness of ultrasound examinations), low Apgar score (1.6, 1.1-1.2; 1.9, 1.3-2.7; and 2.1, 1.5-2.8 respectively for appropriateness and promptness of gynaecological visits, and appropriateness of ultrasound examinations), and low birth weight (1.8, 1.5-2.3 for appropriateness of laboratory test examinations). Benefits for mothers and newborn are expected from improving adherence to guidelines-driven recommendations regarding antenatal care even for low-risk, uncomplicated pregnancies.