Assessing Obstetrical and Perinatal Outcomes Associated with Maternal Tdap Immunization
Bibliographic record
Abstract
Background: In February 2018, Canada’s National Advisory Committee on Immunization (NACI) began recommending maternal immunization with pertussis-containing vaccine (Tetanus-diphtheria-acellular pertussis [Tdap]) during every pregnancy as a strategy to prevent pertussis infection in young infants. As a baseline for future evaluation of the NACI policy, this thesis aimed to describe the characteristics of women who received Tdap immunization during pregnancy in the pre-policy time period and assess the relationship between maternal Tdap immunization with obstetrical and perinatal outcomes. Methods: We performed a population-based retrospective cohort study of all live births in Ontario, from April 2012 to March 2017 using multiple linked provincial health administrative databases. Tdap immunization during pregnancy was ascertained using Tdap-specific immunization fee codes. We used an extended Cox regression model with a time-dependent exposure variable to estimate adjusted hazards ratios (aHR) for preterm and very preterm birth. All other outcomes (gestational hypertension, chorioamnionitis, small-for-gestational-age birth, neonatal intensive care unit admissions >24 hours, composite outcome for neonatal morbidity) were assessed using log-binomial regression to generate adjusted risk ratios (aRR). All estimates were adjusted using inverse probability of treatment weights derived from propensity scores. Results: Of the 621,903 pregnancies ending in a live birth, 11,750 (1.9%) women received Tdap during pregnancy. The maternal Tdap vaccination rate increased by 8-fold across the study time period, from 4.6 per 1000 women in fiscal-year 2012 to 39.1 per 1000 women in fiscal-year 2016. Women who were nulliparous, residing in a higher-income neighbourhood, and receiving adequate or intensive prenatal care had the highest vaccination rates. There were no significant increased risks (aHR/aRR [95% CI]) for preterm birth (0.99 [0.87-1.12]), very preterm birth (1.03 [0.71-1.50]), or small-for-gestational-age birth (0.95 [0.90-1.02]) in Tdap-exposed infants. A significant reduction in risk for neonatal hospitalization and morbidity (measured by a composite outcome) was found among exposed infants; however, these associations were attenuated following sensitivity analyses. Among Tdap-vaccinated women, compared to unvaccinated women, there was no association with chorioamnionitis (0.95 [0.79-1.15]), but a 19% lower risk of gestational hypertension was observed (0.81 [0.74-0.90]). Conclusions: We did not detect any adverse obstetrical or perinatal outcomes following Tdap vaccination during pregnancy. These results complement existing evidence that maternal Tdap vaccination is not associated with adverse outcomes in either the mother or infant. On-going evaluation in Canada is needed as Tdap coverage among pregnant women increases in the coming years.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.011 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 0.002 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".