Table 3.

Association between receipt or no receipt of third covid-19 vaccine dose during pregnancy and adverse pregnancy outcomes

Outcome*	Received third covid-19 vaccine dose (n=18 182)	Did not receive third covid-19 vaccine dose (n=13 943)	Unadjusted hazard ratio†	Adjusted hazard ratio†‡
Hypertensive disorders of pregnancy§	1408 (7.7)	940 (6.7)	1.13 (1.03 to 1.24)	1.03 (0.94 to 1.14)
Placental abruption	263 (1.4)	222 (1.6)	0.91 (0.76 to 1.09)	0.84 (0.70 to 1.02)
Caesarean delivery	5952 (32.7)	4626 (33.2)	0.95 (0.92 to 0.99)	0.90 (0.87 to 0.94)
Emergency caesarean delivery	2405 (13.2)	1840 (13.2)	0.96 (0.90 to 1.02)	0.90 (0.85 to 0.96)
Chorioamnionitis	94 (0.5)	92 (0.7)	0.74 (0.56 to 0.99)	0.67 (0.49 to 0.90)
Postpartum hemorrhage	634 (3.5)	446 (3.2)	1.04 (0.92 to 1.18)	1.01 (0.89 to 1.16)

Data are number (percentage with outcome) or hazard ratio (95% confidence interval).

*Among unique pregnancies (n=32 125).

†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.

§To ensure the correct temporal order of the exposure-outcome association, the model included only individuals who received a third covid-19 vaccine dose before 20 weeks of gestation as gestational hypertensive disorders are diagnosed after 20 weeks of gestation. Individuals vaccinated on or after 20 weeks of gestation were excluded from the analysis.