Association between receipt of tetanus–diphtheria–acellular pertussis vaccine during pregnancy and obstetric and perinatal outcomes using propensity score weighting
| Outcome | No. (%) of maternal–infant pairs | Crude estimate, RR or HR (95% CI) | IPTW-adjusted estimate,* RR or HR (95% CI) | |
|---|---|---|---|---|
| Vaccinated | Unvaccinated | |||
| Cohort 1 (live birth + stillbirth records) | n = 11 519 | n = 603 694 | ||
| Chorioamnionitis† | 139 (1.2) | 6081 (1.0) | 1.20 (1.01–1.42) | 1.17 (0.99–1.39) |
| Gestational hypertension† | 388 (3.4) | 23 087 (3.8) | 0.88 (0.80–0.97) | 0.87 (0.78–0.96) |
| Postpartum hemorrhage† | 324 (2.8) | 16 916 (2.8) | 1.00 (0.90–1.12) | 1.01 (0.91–1.13) |
| Severe postpartum hemorrhage†‡ | 31 (0.3) | 2002 (0.3) | 0.81 (0.57–1.16) | 0.79 (0.55–1.13) |
| Preterm birth (< 37 wk)§¶ | 670 (5.8) | 44 929 (7.4) | 0.99 (0.92–1.07) | 0.98 (0.91–1.06) |
| Very preterm birth (< 32 wk)§¶ | 66 (0.6) | 7945 (1.3) | 1.09 (0.85–1.39) | 1.10 (0.86–1.41) |
| Stillbirth§ | 36 (0.3) | 3249 (0.5) | 0.99 (0.71–1.38) | 1.15 (0.82–1.60) |
| Cohort 2 (live birth records only) | n = 11 483 | n = 600 445 | ||
| Small for gestational age† | 1053 (9.2) | 57 049 (9.5) | 0.97 (0.91–1.02) | 0.96 (0.90–1.02) |
| Neonatal intensive care unit stay > 24 h† | 713 (6.2) | 46 271 (7.7) | 0.81 (0.75–0.87) | 0.82 (0.76–0.88) |
| Composite neonatal morbidity†** | 642 (5.6) | 42 029 (7.0) | 0.80 (0.74–0.86) | 0.81 (0.75–0.87) |
Note: CI = confidence interval, HR = hazard ratio, IPTW = inverse probability of treatment weight, RR = risk ratio.
↵* Stabilized IPTWs were used to adjust estimates.
↵† Estimate values represent RRs that were computed with a log-binomial regression model.
↵‡ Postpartum hemorrhage in conjunction with a procedure code for hysterectomy, blood transfusion or other procedure to control bleeding.
↵§ Estimate values represent HRs that were computed with a Cox model, where tetanus–diphtheria–acellular pertussis (Tdap) vaccination was modelled as a time-varying exposure.
↵¶ Mothers who received Tdap vaccine after 36 weeks’ gestation or 31 weeks’ gestation were treated as unvaccinated in the analyses of preterm birth and very preterm birth, respectively.
↵** Adaptation (39) of a composite indicator for neonatal morbidity (40) that flags infants with 1 or more of 15 neonatal diagnoses or 7 procedures within 28 days after birth (codes provided in Appendix 1, Supplemental Tables S2 and S3).