Table 4.
Association between third covid-19 vaccine dose received during pregnancy and adverse fetal and neonatal outcomes
| Outcome* | Received third covid-19 vaccine dose during pregnancy | Did not receive third covid-19 vaccine dose during pregnancy | Unadjusted hazard ratio† | Adjusted hazard ratio†‡‡ |
| All live births and stillbirths | 18 491 | 14 198 | — | — |
| Stillbirth | 54 (0.29) | 89 (0.63) | 0.60 (0.43 to 0.85) | 0.56 (0.39 to 0.81) |
| Preterm birth <37 weeks | 1452 (7.9) | 1276 (9.0) | 0.93 (0.86 to 1.00) | 0.91 (0.84 to 0.99) |
| Spontaneous preterm birth <37 weeks § | 826 (4.5) | 761 (5.4) | 0.91 (0.82 to 1.00) | 0.93 (0.83 to 1.03) |
| Clinician initiated preterm birth <37 weeks § | 626 (3.4) | 515 (3.6) | 0.95 (0.85 to 1.07) | 0.90 (0.79 to 1.02) |
| Very preterm birth <32 weeks | 197 (1.1) | 255 (1.8) | 0.79 (0.65 to 0.95) | 0.83 (0.68 to 1.03) |
| Live births | 18 437 | 14 109 | — | — |
| NICU admission >24 h ¶ | 2173 (11.8) | 1773 (12.6) | 0.94 (0.88 to 1.00) | 0.96 (0.90 to 1.03) |
| 5 min Apgar score <7 ** | 366 (2.0) | 288 (2.1) | 1.00 (0.86 to 1.17) | 0.96 (0.82 to 1.14) |
| Singleton live births | 17 614 | 13 406 | — | — |
| Small-for-gestational age infant | 1495 (8.5) | 1326 (9.9) | 0.82 (0.76 to 0.88) | 0.86 (0.79 to 0.93) |
Data are number, number (percentage with outcome), or hazard ratio (95% confidence interval). NICU=neonatal intensive care unit.
*End of follow-up: 36+6 weeks of gestation (pregnancy day 258) for preterm birth; 31+6 weeks of gestation (pregnancy day 223) for very preterm birth; and end of pregnancy for all other outcomes.
†Hazard ratios were estimated using an extended Cox model with a time varying exposure variable for third dose of covid-19 vaccine received during pregnancy, after 20 weeks’ gestation. Since vaccination status was treated as a time varying variable, individuals vaccinated after 20 weeks could have contributed both unexposed and exposed follow-up time. In all models, the reference category was unexposed follow-up time.
‡Model was performed on ten multiple imputation datasets and adjusted using stabilised inverse probability of treatment weights derived from a propensity score model including the variables listed in online supplemental table 2.
§For spontaneous preterm birth, clinician initiated preterm births were censored at delivery. For clinician initiated preterm birth, spontaneous preterm births were censored at delivery.
¶Due to missing values for this outcome, the denominator for the exposed group was 18 427 live births and for the unexposed group was 14 095 live births.
**Due to missing values for this outcome, the denominator for the exposed group was 18 005 live births and for the unexposed group was 13 799 live births.