Table 1.
Personal characteristics of study population overall and by covid-19 vaccination status during pregnancy. Values are numbers (percentages) unless stated otherwise
| Characteristics | Unweighted | Stabilised inverse probability of treatment weighted | ||||||
|---|---|---|---|---|---|---|---|---|
| Live births and stillbirths (n=85 162)* | ≥1 vaccine dose during pregnancy (n=43 099)* | No vaccine during pregnancy (n=42 063)* | Standardised difference† | ≥1 vaccine dose during pregnancy* (%) | No vaccine during pregnancy* (%) | Standardised difference† | ||
| Maternal age (years) | ||||||||
| <25 | 6877 (8.1) | 1836 (4.3) | 5041 (12.0) | 0.29 | 6.7 | 9.0 | 0.08 | |
| 25-29 | 20 338 (23.9) | 8652 (20.1) | 11 686 (27.8) | 0.18 | 23.3 | 24.3 | 0.03 | |
| 30-34 | 34 350 (40.3) | 19 127 (44.4) | 15 223 (36.2) | 0.17 | 43.3 | 36.9 | 0.13 | |
| 35-39 | 19 405 (22.8) | 11 287 (26.2) | 8118 (19.3) | 0.16 | 22.7 | 22.9 | 0.00 | |
| ≥40 | 4192 (4.9) | 2197 (5.1) | 1995 (4.7) | 0.02 | 4.0 | 6.9 | 0.13 | |
| Mean (SD) age | 32.1 (4.9) | 32.9 (4.4) | 31.3 (5.3) | 0.05 | 32.1 (4.6) | 32.2 (5.3) | 0.01 | |
| Estimated date of conception | ||||||||
| Before Sept 2020 | 7059 (8.3) | 2376 (5.5) | 4683 (11.1) | 0.20 | 6.7 | 9.1 | 0.09 | |
| Sept-Oct 2020 | 24 396 (28.6) | 11 309 (26.2) | 13 087 (31.1) | 0.11 | 29.8 | 27.3 | 0.05 | |
| Nov-Dec 2020 | 24 470 (28.7) | 12 586 (29.2) | 11 884 (28.3) | 0.02 | 29.3 | 28.3 | 0.02 | |
| Jan-Feb 2021 | 21 922 (25.7) | 12 538 (29.1) | 9384 (22.3) | 0.16 | 26.0 | 25.7 | 0.01 | |
| After Feb 2021 | 7315 (8.6) | 4290 (10.0) | 3025 (7.2) | 0.10 | 8.3 | 9.5 | 0.04 | |
| Parity | ||||||||
| 0 (nulliparous) | 36 932 (43.4) | 19 689 (45.7) | 17 243 (41.0) | 0.09 | 43.6 | 43.7 | 0.00 | |
| ≥1 (multiparous) | 47 835 (56.2) | 23 176 (53.8) | 24 659 (58.6) | 0.10 | 56.4 | 56.3 | 0.00 | |
| Missing‡ | 395 (0.5) | 234 (0.5) | 161 (0.4) | 0.02 | ||||
| Multiple birth | ||||||||
| Yes | 2416 (2.8) | 1235 (2.9) | 1181 (2.8) | 0.00 | 2.8 | 2.9 | 0.00 | |
| No | 82 746 (97.2) | 41 864 (97.1) | 40 882 (97.2) | 0.00 | 97.2 | 97.1 | 0.00 | |
| Pre-existing medical condition§ | ||||||||
| Yes | 9474 (11.1) | 5253 (12.2) | 4221 (10.0) | 0.07 | 11.2 | 11.2 | 0.00 | |
| Thyroid disease | 5018 (5.9) | 2957 (6.9) | 2061 (4.9) | 0.08 | 6.1 | 5.8 | 0.01 | |
| Asthma | 3279 (3.9) | 1683 (3.9) | 1596 (3.8) | 0.01 | 3.7 | 3.9 | 0.01 | |
| Diabetes | 910 (1.1) | 483 (1.1) | 427 (1.0) | 0.01 | 1.1 | 1.1 | 0.00 | |
| Chronic hypertension | 761 (0.9) | 414 (1.0) | 347 (0.8) | 0.01 | 0.9 | 0.9 | 0.01 | |
| Heart disease | 100 (0.1) | 56 (0.1) | 44 (0.1) | 0.01 | 0.1 | 0.1 | 0.00 | |
| Smoked during pregnancy | ||||||||
| No | 78 103 (91.7) | 40 566 (94.1) | 37 537 (89.2) | 0.18 | 93.4 | 93.7 | 0.01 | |
| Yes | 5168 (6.1) | 1461 (3.4) | 3707 (8.8) | 0.23 | 6.6 | 6.3 | 0.01 | |
| Missing‡ | 1891 (2.2) | 1072 (2.5) | 819 (1.9) | 0.04 | ||||
| Substance use during pregnancy¶ | ||||||||
| No | 78 346 (92.0) | 40 282 (93.5) | 38 064 (90.5) | 0.11 | 94.7 | 94.9 | 0.01 | |
| Yes | 3958 (4.6) | 1264 (2.9) | 2694 (6.4) | 0.17 | 5.3 | 5.1 | 0.01 | |
| Missing‡ | 2858 (3.4) | 1553 (3.6) | 1305 (3.1) | 0.03 | ||||
| Prepregnancy BMI | ||||||||
| <30 | 60 358 (70.9) | 31 024 (72.0) | 29 334 (69.7) | 0.05 | 78.8 | 78.9 | 0.00 | |
| ≥30 (obese) | 16 100 (18.9) | 7972 (18.5) | 8128 (19.3) | 0.02 | 21.2 | 21.1 | 0.00 | |
| Missing‡ | 8704 (10.2) | 4103 (9.5) | 4601 (10.9) | 0.05 | ||||
| Neighbourhood median family income fifth | ||||||||
| First (lowest) | 17 118 (20.1) | 7081 (16.4) | 10 037 (23.9) | 0.19 | 20.5 | 20.3 | 0.00 | |
| Second | 17 037 (20.0) | 8144 (18.9) | 8893 (21.1) | 0.06 | 20.1 | 20.2 | 0.00 | |
| Third | 17 973 (21.1) | 9154 (21.2) | 8819 (21.0) | 0.01 | 21.2 | 21.3 | 0.00 | |
| Fourth | 17 994 (21.1) | 9989 (23.2) | 8005 (19.0) | 0.10 | 21.3 | 21.3 | 0.00 | |
| Fifth (highest) | 14 271 (16.8) | 8525 (19.8) | 5746 (13.7) | 0.16 | 16.9 | 16.9 | 0.00 | |
| Missing‡ | 769 (0.9) | 206 (0.5) | 563 (1.3) | 0.09 | ||||
| Rural residence** | ||||||||
| No | 73 112 (85.9) | 37 896 (87.9) | 35 216 (83.7) | 0.12 | 85.6 | 85.8 | 0.01 | |
| Yes | 12 050 (14.1) | 5203 (12.1) | 6847 (16.3) | 0.12 | 14.4 | 14.2 | 0.01 | |
| Public health unit region of residence | ||||||||
| Central east | 23 780 (27.9) | 11 883 (27.6) | 11 897 (28.3) | 0.02 | 28.4 | 28.4 | 0.00 | |
| Central west | 18 006 (21.1) | 8824 (20.5) | 9182 (21.8) | 0.03 | 21.2 | 21.3 | 0.00 | |
| Greater Toronto region | 16 620 (19.5) | 9508 (22.1) | 7112 (16.9) | 0.13 | 19.6 | 19.7 | 0.00 | |
| Eastern | 11 224 (13.2) | 6347 (14.7) | 4877 (11.6) | 0.09 | 13.2 | 13.2 | 0.00 | |
| South west | 10 494 (12.3) | 4478 (10.4) | 6016 (14.3) | 0.12 | 12.2 | 12.3 | 0.00 | |
| North east | 2889 (3.4) | 1229 (2.9) | 1660 (3.9) | 0.06 | 3.5 | 3.4 | 0.00 | |
| North west | 1390 (1.6) | 631 (1.5) | 759 (1.8) | 0.03 | 1.8 | 1.7 | 0.01 | |
| Missing‡ | 759 (0.9) | 199 (0.5) | 560 (1.3) | 0.09 | ||||
| Residential instability fifth | ||||||||
| First (least) | 17 007 (20.0) | 8818 (20.5) | 8189 (19.5) | 0.02 | 20.1 | 20.2 | 0.00 | |
| Second | 15 810 (18.6) | 8181 (19.0) | 7629 (18.1) | 0.02 | 18.8 | 18.8 | 0.00 | |
| Third | 16 032 (18.8) | 8167 (18.9) | 7865 (18.7) | 0.01 | 19.1 | 19.1 | 0.00 | |
| Fourth | 15 528 (18.2) | 7713 (17.9) | 7815 (18.6) | 0.02 | 18.6 | 18.5 | 0.00 | |
| Fifth (most) | 19 286 (22.6) | 9743 (22.6) | 9543 (22.7) | 0.00 | 23.4 | 23.4 | 0.00 | |
| Missing‡ | 1499 (1.8) | 477 (1.1) | 1022 (2.4) | 0.10 | ||||
| Material deprivation fifth | ||||||||
| First (least) | 19 351 (22.7) | 11 855 (27.5) | 7496 (17.8) | 0.23 | 23.0 | 23.1 | 0.00 | |
| Second | 17 132 (20.1) | 9481 (22.0) | 7651 (18.2) | 0.10 | 20.3 | 20.4 | 0.00 | |
| Third | 15 461 (18.2) | 7776 (18.0) | 7685 (18.3) | 0.01 | 18.3 | 18.3 | 0.00 | |
| Fourth | 15 279 (17.9) | 7145 (16.6) | 8134 (19.3) | 0.07 | 18.3 | 18.2 | 0.00 | |
| Fifth (most) | 16 440 (19.3) | 6365 (14.8) | 10 075 (24.0) | 0.23 | 20.1 | 20.0 | 0.00 | |
| Missing‡ | 1499 (1.8) | 477 (1.1) | 1022 (2.4) | 0.10 | ||||
| Dependency fifth | ||||||||
| First (least) | 27 572 (32.4) | 14 761 (34.2) | 12 811 (30.5) | 0.08 | 32.8 | 32.8 | 0.00 | |
| Second | 17 547 (20.6) | 8958 (20.8) | 8589 (20.4) | 0.01 | 20.8 | 20.9 | 0.00 | |
| Third | 14 076 (16.5) | 7104 (16.5) | 6972 (16.6) | 0.00 | 16.9 | 16.9 | 0.00 | |
| Fourth | 12 749 (15.0) | 6211 (14.4) | 6538 (15.5) | 0.03 | 15.2 | 15.2 | 0.00 | |
| Fifth (most) | 11 719 (13.8) | 5588 (13.0) | 6131 (14.6) | 0.05 | 14.3 | 14.2 | 0.00 | |
| Missing‡ | 1499 (1.8) | 477 (1.1) | 1022 (2.4) | 0.10 | ||||
| Ethnic concentration fifth | ||||||||
| First (lowest) | 11 634 (13.7) | 5357 (12.4) | 6277 (14.9) | 0.07 | 14.4 | 14.2 | 0.01 | |
| Second | 13 640 (16.0) | 6878 (16.0) | 6762 (16.1) | 0.00 | 16.3 | 16.3 | 0.00 | |
| Third | 15 114 (17.7) | 8251 (19.1) | 6863 (16.3) | 0.07 | 17.8 | 17.9 | 0.00 | |
| Fourth | 18 378 (21.6) | 9898 (23.0) | 8480 (20.2) | 0.07 | 21.8 | 21.9 | 0.00 | |
| Fifth (highest) | 24 897 (29.2) | 12 238 (28.4) | 12 659 (30.1) | 0.04 | 29.6 | 29.7 | 0.00 | |
| Missing‡ | 1499 (1.8) | 477 (1.1) | 1022 (2.4) | 0.10 | ||||
BMI=body mass index; SD=standard deviation.
*
Column percentages in the weighted study population were based on imputation dataset 1.
†
Absolute standardised difference comparing those who received one dose or more of a covid-19 vaccine during pregnancy and those who were not vaccinated during pregnancy; standardised difference >0.10 indicates an imbalance in the distribution of the baseline characteristic between these two vaccination groups.
‡
Missing data are not shown in the weighted study population as multiple imputation was used before deriving inverse probability of treatment weights.
§
Composite of asthma, chronic hypertension, diabetes, heart disease, thyroid disease. Sum of individual conditions does not equal the total number of individuals with any individual condition, as categories were not mutually exclusive.
¶
Self-reported cannabis, opioid, or alcohol use during pregnancy.
**
Because of small cell counts (<6) for missing values in the vaccinated group, missing has been combined with the “no” category.