Immortal time bias in drug safety cohort studies: spontaneous abortion following nonsteroidal antiinflammatory drug exposure

Exposure to Macrolides During Pregnancy and the Risk for Spontaneous Abortions: A Population-Based Retrospective Cohort Study

Previous studies evaluating the risk of spontaneous abortions following exposure to macrolides reported controversial results. The goal of the current study was to examine the risk for spontaneous abortions following exposure to macrolides during pregnancy. We conducted a population-based retrospective cohort study by linking three computerized databases: Clalit Health Services drug dispensation database, Soroka Medical Center (SMC) birth database, and SMC hospitalizations database. Multivariate time-varying Cox regressions were performed and adjusted for suspected confounders and known risk factors for spontaneous abortions. Hazard ratios (HR) and 95% confidence intervals (CI) were calculated. A secondary analysis was performed to assess the association between exposure to macrolides in terms of the defined daily dose dispensed and spontaneous abortions. The study cohort included 65,457 pregnancies that ended at Soroka Medical Center between 2004 and 2009, of which 6508 (9.9%) resulted in a spontaneous abortion. A total of 825 (1.26%) pregnancies were exposed to macrolides during the exposure period. Exposure to macrolides was not associated with spontaneous abortions as a group (adjusted HR 1.00 95% CI 0.77-1.31) or as specific medications. There was no evidence of a dose-response relationship between exposure to macrolides and spontaneous abortions. In conclusion, this population-based retrospective cohort study did not detect an increased risk for spontaneous abortion following exposure to macrolides during the first trimester of pregnancy.

Miscarriage after SARS-CoV-2 vaccination: A population-based cohort study

OBJECTIVE

To evaluate the risk of miscarriage following SARS-CoV-2 vaccination, while accounting for the competing risk of induced abortion.

DESIGN

Population-based cohort study.

SETTING

Ontario, Canada.

PARTICIPANTS

Women aged 15-50 years with a confirmed pregnancy at ≤19 completed weeks' gestation.

METHODS

Exposure to first SARS-CoV-2 vaccination, handled in a time-varying manner, was defined as (i) unvaccinated, (ii) remotely vaccinated >28 days before the estimated conception date or (iii) recently vaccinated ≤28 days before conception and up to 120 days after conception.

MAIN OUTCOME MEASURES

The outcome was miscarriage, occurring between the estimated date of conception and up to 19 completed weeks of pregnancy. Fine-Grey hazard models, accounting for the competing risk of induced abortion, generated hazard ratios (aHR), adjusted for socio-demographic factors, comorbidities, and biweekly periods.

RESULTS

Included were 246 259 pregnant women, of whom 34% received a first SARS-CoV-2 vaccination. Miscarriage occurred at a rate of 3.6 per 10 000 person-days among remotely vaccinated women and 3.2 per 10 000 person-days among those recently vaccinated, in contrast to a rate of 1.9 per 10 000 person-days among unvaccinated women, with corresponding aHR of 0.98 (95% confidence interval [CI] 0.91-1.07) and 1.00 (95% CI 0.93-1.08).

CONCLUSIONS

SARS-CoV-2 vaccination was not associated with miscarriage while accounting for the competing risk of induced abortion. This study reiterates the importance of including pregnant women in new vaccine clinical trials and registries, and the rapid dissemination of vaccine safety data.

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.

Pregnancy outcomes following maternal macrolide use: A systematic review and meta-analysis

To determine whether gestational use of all or specific macrolides (azithromycin, clarithromycin, roxithromycin or erythromycin) lead to an increase in rates of overall major congenital malformations, organ-specific malformations, and other adverse pregnancy outcomes in infants. PubMed/MEDLINE, Cochrane Central Register of Controlled Trials and Reprotox® databases were searched. Dichotomous outcomes or calculated log odds ratios and standard errors from observational studies are combined using the random-effects method in Review Manager 5.3. No significant increased risks for major congenital malformation (OR 1.06 [95% CI 0.99, 1.13]) and congenital heart defect (OR 1.05 [95% CI 0.92, 1.19]) following all macrolides use during the first trimester were detected. Prenatal azithromycin use was associated with a significantly increased risk of major congenital malformations in the analysis of cohort studies (OR 1.21 [95% CI 1.08-1.36]). This significance was also present in the sensitivity analysis. There were no statistically significant associations between the risk of organ specific malformations and all or specific macrolide exposures except for the decreased risk in hypospadias following erythromycin use in the meta-analysis of case-control studies (OR 0.38 [95% CI 0.18, 0.81]. Also, a significant 1.5-fold increased risk for spontaneous abortion following macrolide use was detected. A slight yet significantly increased rate of major congenital malformation with azithromycin exposure during pregnancy may be associated with maternal confounders. Nevertheless, level II ultrasound can be suggested following maternal azithromycin use during the first trimester. Future studies should take into account the inclusion of a disease-matched control group and accurate classification of the malformations.

Time-related biases in perinatal pharmacoepidemiology: A systematic review of observational studies

BACKGROUND

Time-related biases, such as immortal time and time-window bias, frequently occur in pharmacoepidemiologic research. However, the prevalence of these biases in perinatal pharmacoepidemiology is not well understood.

OBJECTIVE

To describe the frequency of time-related biases in observational studies of medications commonly used during pregnancy (antibiotic, antifungal, and antiemetic drugs) via systematic review.

METHOD

We searched Medline and EMBASE for observational studies published between January 2013 and September 2020 and examining the association between antibiotic, antifungal, or antiemetic drugs and adverse pregnancy outcomes, including spontaneous abortion, stillbirth, preterm delivery, small-for-gestational age, pre-eclampsia, and gestational diabetes. The proportion of studies with time-related biases was estimated overall and by type (immortal time bias, time-window bias).

RESULTS

Our systematic review included 20 studies (16 cohort studies, 3 nested case-control studies, and 1 case-control study), of which 12 examined antibiotic, 6 antiemetic, and 2 anti-fungal drugs. Eleven studies (55%) had immortal time bias due to the misclassification of unexposed, event-free person-time between cohort entry and exposure initiation as exposed. No included study had time-window bias. The direction of effect varied for both studies with and without time-related bias, with many studies reporting very wide confidence intervals around the effect estimates, thus making the direction of effect less interpretable. However, studies with time-related bias were more likely to show protective or null associations compared with studies without time-related bias.

CONCLUSION

Time-related biases occur frequently in observational studies of drug effects during pregnancy. The use of appropriate study design and analytical approaches is needed to prevent time-related biases and ensure study validity.

Associations Between Late-Onset Preeclampsia and the Use of Calcium-Based Antacids and Proton Pump Inhibitors During Pregnancy: A Prospective Cohort Study

Purpose

Preeclampsia is a leading cause of maternal morbidity and mortality. Calcium-based antacids and proton pump inhibitors (PPIs) are commonly used during pregnancy to treat symptoms of gastroesophageal reflux disease. Both have been hypothesized to reduce the risk of preeclampsia. We determined associations of calcium-based antacid and PPI use during pregnancy with late-onset preeclampsia (≥34 weeks of gestation), taking into account dosage and timing of use.

Patients and Methods

We included 9058 pregnant women participating in the PRIDE Study (2012–2019) or The Dutch Pregnancy Drug Register (2014–2019), two prospective cohorts in The Netherlands. Data were collected through web-based questionnaires and obstetric records. We estimated risk ratios (RRs) for late-onset preeclampsia for any use and trajectories of calcium-based antacid and PPI use before gestational day 238, and hazard ratios (HRs) for time-varying exposures after gestational day 237.

Results

Late-onset preeclampsia was diagnosed in 2.6% of pregnancies. Any use of calcium-based antacids (RR 1.2 [95% CI 0.9–1.6]) or PPIs (RR 1.4 [95% CI 0.8–2.4]) before gestational day 238 was not associated with late-onset preeclampsia. Use of low-dose calcium-based antacids in gestational weeks 0–16 (<1 g/day; RR 1.8 [95% CI 1.1–2.9]) and any use of PPIs in gestational weeks 17–33 (RR 1.6 [95% CI 1.0–2.8]) seemed to increase risks of late-onset preeclampsia. We did not observe associations between late-onset preeclampsia and use of calcium-based antacids (HR 1.0 [95% CI 0.6–1.5]) and PPIs (HR 1.4 [95% CI 0.7–2.9]) after gestational day 237.

Conclusion

In this prospective cohort study, use of calcium-based antacids and PPIs during pregnancy was not found to reduce the risk of late-onset preeclampsia.

Longitudinal Methods for Modeling Exposures in Pharmacoepidemiologic Studies in Pregnancy

In many perinatal pharmacoepidemiologic studies, exposure to a medication is classified as "ever exposed" versus "never exposed" within each trimester or even over the entire pregnancy. This approach is often far from real-world exposure patterns, may lead to exposure misclassification, and does not to incorporate important aspects such as dosage, timing of exposure, and treatment duration. Alternative exposure modeling methods can better summarize complex, individual-level medication use trajectories or time-varying exposures from information on medication dosage, gestational timing of use, and frequency of use. We provide an overview of commonly used methods for more refined definitions of real-world exposure to medication use during pregnancy, focusing on the major strengths and limitations of the techniques, including the potential for method-specific biases. Unsupervised clustering methods, including k-means clustering, group-based trajectory models, and hierarchical cluster analysis, are of interest because they enable visual examination of medication use trajectories over time in pregnancy and complex individual-level exposures, as well as providing insight into comedication and drug-switching patterns. Analytical techniques for time-varying exposure methods, such as extended Cox models and Robins' generalized methods, are useful tools when medication exposure is not static during pregnancy. We propose that where appropriate, combining unsupervised clustering techniques with causal modeling approaches may be a powerful approach to understanding medication safety in pregnancy, and this framework can also be applied in other areas of epidemiology.

Association of Inadvertent 9-Valent Human Papillomavirus Vaccine in Pregnancy With Spontaneous Abortion and Adverse Birth Outcomes

IMPORTANCE

The 9-valent human papillomavirus (9vHPV) vaccine is recommended for individuals through age 26 years and may be administered to women up to age 45 years. Data on 9vHPV vaccine exposures during pregnancy are limited.

OBJECTIVE

To evaluate the associations between 9vHPV vaccine exposures during pregnancy or peripregnancy and selected pregnancy and birth outcomes (spontaneous abortion [SAB], preterm birth, small-for-gestational age [SGA] birth, and major structural birth defect).

DESIGN, SETTING, AND PARTICIPANTS

This cohort study analyzed data from 7 participating health systems in the Vaccine Safety Datalink. The cohort comprised pregnancies among girls and women aged 12 to 28 years that ended between October 26, 2015, and November 15, 2018. Singleton pregnancies that ended in a live birth, stillbirth, or SAB were included.

EXPOSURES

Vaccine exposure windows were distal (9vHPV or 4vHPV vaccine administered from 22 to 16 weeks before last menstrual period [LMP]), peripregnancy (9vHPV vaccine administered from 42 days before LMP until LMP), and during pregnancy (9vHPV vaccine administered from LMP to 19 completed weeks' gestation). Primary comparisons were (1) girls and women with 9vHPV vaccine exposures during pregnancy vs those with 4vHPV or 9vHPV distal vaccine exposures, (2) girls and women with vaccine exposures peripregnancy vs those with 4vHPV or 9vHPV distal vaccine exposures, and (3) girls and women with 9vHPV vaccine exposures during pregnancy or peripregnancy vs those with 4vHPV or 9vHPV distal vaccine exposure.

MAIN OUTCOMES AND MEASURES

Spontaneous abortions were confirmed based on medical record review and adjudication. Preterm and SGA births were identified from electronic health record and birth data. Major structural birth defects were based on diagnostic codes using a validated algorithm. Inverse probability weighting was used to balance the covariates. Time-dependent covariate Cox proportional hazards regression models and Poisson regression were used to estimate the associations between 9vHPV vaccine exposures and pregnancy and birth outcomes.

RESULTS

The final cohort included 1493 pregnancies among girls and women with a mean (SD) maternal age of 23.9 (2.9) years. Of these pregnancies, 445 (29.8%) had exposures to the 9vHPV vaccine during pregnancy, 496 (33.2%) had exposures to the 9vHPV vaccine peripregnancy, and 552 (37.0%) had 4vHPV or 9vHPV distal vaccine exposures. The 9vHPV vaccine administered during pregnancy was not associated with increased risk for SAB (hazard ratio, 1.12; 95% CI, 0.66-1.93) compared with distal vaccine exposures. Findings were similar for 9vHPV vaccine exposures peripregnancy (relative risk [RR], 0.72; 95% CI, 0.42-1.24). Among live births (n = 1409), 9vHPV vaccine exposures during pregnancy were not associated with increased risks for preterm birth (RR, 0.73; 95% CI, 0.44-1.20) or SGA birth (RR, 1.31; 95% CI, 0.78-2.20). Results were similar regarding the association between 9vHPV vaccine exposures peripregnancy and preterm birth (RR, 0.72; 95% CI, 0.45-1.17) and SGA birth (RR, 1.10; 95% CI, 0.65-1.88). Birth defects were rare in all exposure groups, occurring in about 1% of live births with available infant data.

CONCLUSIONS AND RELEVANCE

This study found that 9vHPV vaccine exposures during or around the time of pregnancy were uncommon and not associated with SABs or selected adverse birth outcomes. These findings can inform counseling for inadvertent 9vHPV vaccine exposures.

Educational note: addressing special cases of bias that frequently occur in perinatal epidemiology

The epidemiologic study of pregnancy and birth outcomes may be hindered by several unique and challenging issues. Pregnancy is a time-limited period in which severe cohort attrition takes place between conception and birth and adverse outcomes are complex and multi-factorial. Biases span those familiar to epidemiologists: selection, confounding and information biases. Specific challenges include conditioning on potential intermediates, how to treat race/ethnicity, and influential windows of prolonged, seasonal and potentially time-varying exposures. Researchers studying perinatal outcomes should be cognizant of the potential pitfalls due to these factors and address their implications with respect to formulating questions of interest, choice of an appropriate analysis approach and interpretations of findings given assumptions. In this article, we catalogue some of the more important potential sources of bias in perinatal epidemiology that have more recently gained attention in the literature, provide the epidemiologic context behind each issue and propose practices for dealing with each issue to the extent possible.

Power in numbers

Collecting useful data on a sufficiently large cohort of pregnancies in women with rheumatic disease is a challenge. The original manuscripts that demonstrated the dangers of pregnancy in women with lupus were relatively small case series. As larger prospective cohorts were collected by university-based experts, however, greater safety was demonstrated and the current norms of treatment were determined. In recent years, larger administrative databases have been tapped to study pregnancies not managed within university clinics and to study the long-term impact of maternal rheumatic disease on the offspring. Each of these methods of study has both strengths and weaknesses, adding a unique piece of data to our overall knowledge. We will discuss a range of approaches to the study of rheumatic disease in pregnancy, covering the potential benefits that each brings as well as the biases that can impact study results. When the results of studies are viewed through these lenses, each can contribute to our larger understanding of the rheumatic diseases in pregnancy.

Vaginal antimycotics and the risk for spontaneous abortions

BACKGROUND

Spontaneous abortions are the most common complication of pregnancy. Clotrimazole and miconazole are widely used vaginal-antimycotic agents used for the treatment of vulvovaginal candidiasis. A previous study has suggested an increased risk of miscarriage associated with these azoles, which may lead health professionals to refrain from their use even if clinically indicated.

OBJECTIVE

The aim of the current study was to assess the risk for spontaneous abortions following first trimester exposure to vaginal antimycotics.

STUDY DESIGN

A historical cohort study was conducted including all clinically apparent pregnancies that began from January 2003 through December 2009 and admitted for birth or spontaneous abortion at Soroka Medical Center, Clalit Health Services, Beer-Sheva, Israel. A computerized database of medication dispensation was linked with 2 computerized databases containing information on births and spontaneous abortions. Time-varying Cox regression models were constructed adjusting for mother's age, diabetes mellitus, hypothyroidism, obesity, hypercoagulable or inflammatory conditions, recurrent miscarriages, intrauterine contraceptive device, ethnicity, tobacco use, and the year of admission.

RESULTS

A total of 65,457 pregnancies were included in the study: 58,949 (90.1%) ended with birth and 6508 (9.9%) with a spontaneous abortion. Overall, 3246 (5%) pregnancies were exposed to vaginal antimycotic medications until the 20th gestational week: 2712 (4.2%) were exposed to clotrimazole and 633 (1%) to miconazole. Exposure to vaginal antimycotics was not associated with spontaneous abortions as a group (crude hazard ratio, 1.11; 95% confidence interval, 0.96-1.29; adjusted hazard ratio, 1.11; 95% confidence interval, 0.96-1.29) and specifically for clotrimazole (adjusted hazard ratio, 1.05; 95% confidence interval, 0.89-1.25) and miconazole (adjusted hazard ratio, 1.34; 95% confidence interval, 0.99-1.80). Furthermore, no association was found between categories of dosage of vaginal antimycotics and spontaneous abortions.

CONCLUSION

Exposure to vaginal antimycotics was not associated with spontaneous abortions.

Immortal Time Bias in Observational Studies of Time-to-Event Outcomes: Assessing Effects of Postmastectomy Radiation Therapy Using the National Cancer Database

The objectives of this study are to illustrate the effects of immortal time bias (ITB) using an oncology outcomes database and quantify through simulations the magnitude and direction of ITB when different analytical techniques are used. A cohort of 11 626 women who received neoadjuvant chemotherapy and underwent mastectomy with pathologically positive lymph nodes were accrued from the National Cancer Database (2004-2008). Standard Cox regression, time-dependent (TD), and landmark models were used to compare overall survival in patients who did or did not receive postmastectomy radiation therapy (PMRT). Simulation studies showing ways to reduce the effect of ITB indicate that TD exposures should be included as variables in hazard-based analyses. Standard Cox regression models comparing overall survival in patients who did and did not receive PMRT showed a significant treatment effect (hazard ratio [HR]: 0.93, 95% confidence interval [CI]: 0.88-0.99). Time-dependent and landmark methods estimated no treatment effect with HR: 0.97, 95% CI: 0.92 to 1.03 and HR: 0.98, 95% CI, 0.92 to 1.04, respectively. In our simulation studies, the standard Cox regression model significantly overestimated treatment effects when no effect was present. Estimates of TD models were closest to the true treatment effect. Landmark model results were highly dependent on landmark timing. Appropriate statistical approaches that account for ITB are critical to minimize bias when examining relationships between receipt of PMRT and survival.

No association between influenza vaccination during pregnancy and adverse birth outcomes

BACKGROUND

Pregnant women are recommended to receive inactivated influenza vaccination anytime during pregnancy. Studies have investigated the impact of influenza vaccination during pregnancy on birth outcomes and results on preterm birth have been inconsistent.

METHODS

We conducted a retrospective cohort study among children born at a gestational age≥24weeks from January 1, 2010 to December 31, 2015 at Kaiser Permanente Northern California facilities (KPNC). We evaluated the association between maternal influenza vaccination during pregnancy and risk of preterm birth, small and large for gestational age, admission to the neonatal intensive care unit (NICU), respiratory distress syndrome, low birth weight, and low Apgar score. We ascertained the dates of maternal influenza vaccination, conception, and delivery, as well as birth outcomes from KPNC inpatient and outpatient databases. Conditional multivariate Cox regression and logistic regression analyses were used to determine the association between maternal vaccination during pregnancy and risk of each birth outcome.

RESULTS

The study included 145,869 children. Maternal influenza vaccination during pregnancy was not associated with risk of small or large for gestational age births, preterm birth, need for mechanical ventilation at birth, respiratory distress syndrome, admission to the NICU, low birth weight, or low Apgar score. However, when we did not control for immortal time bias, the risk of preterm birth (odds ratio [OR]=0.69, 95% confidence interval [CI] 0.66-0.72) was lower among infants of vaccinated mothers.

CONCLUSION

We found no association between maternal influenza vaccination during pregnancy and adverse birth outcomes. When investigating preterm birth outcome in association with vaccination during pregnancy, immortal time bias should be taken into account in the analysis.

Constructing Causal Diagrams for Common Perinatal Outcomes: Benefits, Limitations and Motivating Examples with Maternal Antidepressant Use in Pregnancy

BACKGROUND

Covariate selection to reduce bias in observational data analysis has primarily relied upon statistical criteria to guide researchers. This approach may lead researchers to condition on variables that ultimately increase bias in the effect estimates. The use of directed acyclic graphs (DAGs) aids researchers in constructing thoughtful models based on hypothesised biologic mechanisms to produce the least biased effect estimates possible.

METHODS

After providing an overview of different relations in DAGs and the prevailing mechanisms by which conditioning on variables increases or reduces bias in a model, we illustrate examples of DAGs for maternal antidepressants in pregnancy and four separate perinatal outcomes.

RESULTS

By comparing and contrasting the diagrams for maternal antidepressant use in pregnancy and spontaneous abortion, major malformations, preterm birth, and postnatal growth, we illustrate the different conditioning sets required for each model. Moreover, we illustrate why it is not appropriate to condition on the same set of covariates for the same exposure and different perinatal outcomes. We further discuss potential selection biases, overadjustment of mediators on the causal path, and sufficient sets of conditioning variables.

CONCLUSION

In our efforts to construct parsimonious models that minimise confounding and selection biases, we must rely upon our scientific knowledge of the causal mechanism. By structuring data collection and analysis around hypothesised DAGs, we ultimately aim to validly estimate the causal effect of interest.

Invited Commentary: Influenza, Influenza Immunization, and Pregnancy-It's About Time

Immunization of pregnant women against influenza has the potential to reduce adverse fetal outcomes by reducing prenatal exposure to influenza illness. However, as touched on by Fell et al. (Am J Epidemiol. 2016;184(3):163-175) and Vazquez-Benitez et al. (Am J Epidemiol. 2016;184(3):176-186) in this issue of the Journal, observational studies in which the causal effect of maternal influenza illness and influenza immunization on fetal health are evaluated are prone to bias because of the complex temporal nature of influenza illness seasonality, influenza immunization schedules, and gestation itself. Immortal time bias is introduced by an "anytime-in-pregnancy" exposure definition because the shortened pregnancy duration associated with many adverse fetal outcomes limits the opportunity to become exposed, whereas including follow-up time during which pregnancies are no longer at risk of an adverse outcome (e.g., gestational time after 37 weeks in studies of preterm birth) can lead to overestimation of any true benefits of immunization (or harms from influenza illness). We present a framework to avoid time-related biases in the study of influenza illness and immunization in pregnancy and advise that investigations of fetal benefit from maternal influenza immunization should only be undertaken when information is available on the calendar time of influenza virus circulation and the gestational age at which maternal influenza immunization occurred.

Risk of Preterm or Small-for-Gestational-Age Birth After Influenza Vaccination During Pregnancy: Caveats When Conducting Retrospective Observational Studies

Vaccines are increasingly targeted toward women of reproductive age, and vaccines to prevent influenza and pertussis are recommended during pregnancy. Prelicensure clinical trials typically have not included pregnant women, and when they are included, trials cannot detect rare events. Thus, postmarketing vaccine safety assessments are necessary. However, analysis of observational data requires detailed assessment of potential biases. Using data from 8 Vaccine Safety Datalink sites in the United States, we analyzed the association of monovalent H1N1 influenza vaccine (MIV) during pregnancy with preterm birth (<37 weeks) and small-for-gestational-age birth (birth weight < 10th percentile). The cohort included 46,549 pregnancies during 2009-2010 (40% of participants received the MIV). We found potential biases in the vaccine-birth outcome association that might occur due to variable access to vaccines, the time-dependent nature of exposure to vaccination within pregnancy (immortal time bias), and confounding from baseline differences between vaccinated and unvaccinated women. We found a strong protective effect of vaccination on preterm birth (relative risk = 0.79, 95% confidence interval: 0.74, 0.85) when we ignored potential biases and no effect when accounted for them (relative risk = 0.91; 95% confidence interval: 0.83, 1.0). In contrast, we found no important biases in the association of MIV with small-for-gestational-age birth. Investigators conducting studies to evaluate birth outcomes after maternal vaccination should use statistical approaches to minimize potential biases.

Survival and cardiovascular events in men treated with testosterone replacement therapy: an intention-to-treat observational cohort study

BACKGROUND

Conflicting evidence exists for the association between testosterone replacement therapy and mortality and cardiovascular events. The US Food and Drug Administration recently cautioned that testosterone replacement therapy might increase risk of heart attack and stroke, based on evidence from studies with short treatment duration and follow-up. No previous study has assessed the effect of duration of testosterone treatment on these outcomes. We aimed to assess the association between long-term use of testosterone replacement therapy and mortality, cardiovascular events, and prostate cancer diagnoses, using a time-varying exposure analysis.

METHODS

We did a population-based matched cohort study of men aged 66 years or older newly treated with testosterone replacement therapy and controls matched for age, region of residence, comorbidity, diabetes status, and index year from 2007-12 in Ontario, Canada, using data from the Ontario Drug Benefit database, the Canadian Institute for Health Information (CIHI) Discharge Abstract Database, the CIHI National Ambulatory Care Reporting System, the Ontario Health Insurance Plan database, the Ontario Myocardial Infarction Database, the Ontario Diabetes Database, the Ontario Cancer Registry, and the Registered Persons database. We assessed the association between cumulative testosterone replacement therapy exposure and mortality, cardiovascular events, and prostate cancer using marginal models with a time-varying testosterone exposure.

FINDINGS

We included 10 311 men treated with testosterone replacement therapy and 28 029 controls between Jan 1, 2007, and June 30, 2012. Over a median follow-up of 5·3 years (IQR 3·6-7·5) in the testosterone replacement therapy group and 5·1 years (3·4-7·4) in the control group, patients treated with testosterone replacement therapy had lower mortality than did controls (hazard ratio [HR] 0·88, 95% CI 0·84-0·93). Patients in the lowest tertile of testosterone exposure had increased risk of mortality (HR 1·11, 95% CI 1·03-1·20) and cardiovascular events (HR 1·26, 95% CI 1·09-1·46) compared with controls. By contrast, those in the highest tertile of testosterone exposure had decreased risk of mortality (HR 0·67, 95% CI 0·62-0·73) and cardiovascular events (HR 0·84, 95% CI 0·72-0·98), with a significant trend across tertiles (p<0·0001). Risk of prostate cancer diagnosis was decreased for those with the highest tertile of exposure (HR 0·60, 95% CI 0·45-0·80) compared with controls, but not for those with the shortest exposure.

INTERPRETATION

Long-term exposure to testosterone replacement therapy was associated with reduced risks of mortality, cardiovascular events, and prostate cancer. However, testosterone replacement therapy increased the risk of mortality and cardiovascular events with short durations of therapy. In view of the limitations of observational data and the potential for selection bias, these results warrant confirmation in a randomised trial.

FUNDING

Physicians' Services Incorporated Foundation and Ajmera Family Chair in Urologic Oncology.

Interferon-beta exposure during first trimester is safe in women with multiple sclerosis-A prospective cohort study from the German Multiple Sclerosis and Pregnancy Registry

BACKGROUND

Available data suggest that pregnancy exposure to interferon-beta might result in lower mean birth weight and preterm birth.

OBJECTIVE

To determine the effect of interferon-beta exposure during pregnancy on pregnancy outcomes in multiple sclerosis patients.

METHODS

We compared the pregnancy outcomes of women exposed to interferon-beta with pregnancies unexposed to disease-modifying therapies. Women were enrolled into the German Multiple Sclerosis and Pregnancy Registry. A standardized questionnaire was administered during pregnancy and postpartum. Detailed information on course of multiple sclerosis and pregnancy, concomitant medications, delivery, and outcome of pregnancy was obtained.

RESULTS

We collected data on 251 pregnancies exposed to interferon-beta and 194 unexposed to disease-modifying therapies. In all, 246 (98.01%) women discontinued interferon-beta treatment during first trimester. No differences regarding mean birth weight (exposed: 3272.28 ± 563.61 g; unexposed: 3267.46 ± 609.81 g), mean birth length (exposed: 50.73 ± 3.30 cm; unexposed: 50.88 ± 3.45 cm), preterm birth (p = 0.187), spontaneous abortion (p = 0.304), and congenital anomalies (p = 0.197) were observed between the two groups.

CONCLUSIONS

Interferon-beta exposure during early pregnancy does not influence the mean birth weight, risk of preterm birth, or other adverse pregnancy outcomes. Our study provides further reassurance that interferon-beta treatment can be safely continued up until women become pregnant.

Glatiramer acetate during early pregnancy: A prospective cohort study

BACKGROUND

Only limited data are available on whether glatiramer acetate exposure during pregnancy has an effect on perinatal outcome.

OBJECTIVE

To determine the effect of glatiramer acetate exposure during pregnancy on pregnancy outcomes in women with multiple sclerosis.

METHODS

We compared the outcome of pregnancies of women with multiple sclerosis exposed to glatiramer acetate with pregnancies unexposed to disease-modifying therapies. Women were enrolled into the German Multiple Sclerosis and Pregnancy registry. A standardized questionnaire was administered during pregnancy and postpartum. Detailed information on course of multiple sclerosis and pregnancy, concomitant medications, labor, delivery, and outcome of pregnancy was obtained.

RESULTS

We collected data on 246 multiple sclerosis pregnancies, 151 exposed to glatiramer acetate and 95 unexposed to disease-modifying therapies during pregnancy. Three (2.2%) congenital anomalies occurred in the exposed and 6 (6.7%) in the control group. We did not observe an increase in other adverse pregnancy or delivery outcomes including spontaneous abortions, preterm birth, Cesarean sections, or reduced birth weight in the exposed group.

CONCLUSION

Our data provide further evidence that glatiramer acetate exposure during the first trimester of pregnancy appears safe and without teratogenic effect. These findings provide important additive knowledge to better counsel women with multiple sclerosis in planning a pregnancy.