Participant characteristics according to SARS-CoV-2 infection during pregnancy, March 2020-May 2022, in Sweden and Norway
| Characteristics* | Sweden | Norway | ||
| No infection (n=182 810) | SARS-CoV-2 infection (n=18 960) | No infection (n=105 090) | SARS-CoV-2 infection (n=5596) | |
| SARS-CoV-2 vaccination: | ||||
| Vaccinated before pregnancy | 5787 (3.2) | 1839 (9.7) | 643 (0.6) | 406 (7.3) |
| One dose of vaccine during pregnancy | 27 533 (15.1) | 4284 (22.6) | 15 586 (14.8) | 2747 (49.1) |
| Not vaccinated | 149 490 (81.8) | 12 837 (67.7) | 88 861 (84.6) | 2443 (43.7) |
| Maternal age (years): | ||||
| <20 | 2046 (1.1) | 149 (0.8) | 902 (0.9) | 36 (0.6) |
| 20-24 | 18 336 (10.0) | 1852 (9.8) | 10 575 (10.1) | 478 (8.5) |
| 25-29 | 60 887 (33.3) | 6396 (33.7) | 35 796 (34.1) | 1836 (32.8) |
| 30-34 | 66 754 (36.5) | 6980 (36.8) | 39 055 (37.2) | 2197 (39.3) |
| 35-39 | 28 993 (15.9) | 2972 (15.7) | 15 992 (15.2) | 899 (16.1) |
| ≥40 | 5794 (3.2) | 611 (3.2) | 2770 (2.6) | 150 (2.7) |
| Body mass index: | ||||
| <18.5 | 4083 (2.2) | 330 (1.7) | 3253 (3.1) | 158 (2.8) |
| 18.5-<25 | 94 922 (51.9) | 9345 (49.3) | 57 759 (55.0) | 3066 (54.8) |
| 25-<30 | 48 708 (26.6) | 5375 (28.3) | 23 068 (22.0) | 1299 (23.2) |
| ≥30 | 28 039 (15.3) | 3266 (17.2) | 13 765 (13.1) | 737 (13.2) |
| Missing | 7058 (3.9) | 644 (3.4) | 7245 (6.9) | 336 (6.0) |
| Parity: | ||||
| 0 | 79 398 (43.4) | 7496 (39.5) | 46 277 (44.0) | 2092 (37.4) |
| 1 | 67 885 (37.1) | 7142 (37.7) | 38 660 (36.8) | 2061 (36.8) |
| ≥2 | 35 527 (19.4) | 4322 (22.8) | 20 153 (19.2) | 1443 (25.8) |
| Educational level (years): | ||||
| <9 | 16 812 (9.2) | 1465 (7.7) | 13 722 (10.1) | 905 (16.2) |
| 10-12 | 66 543 (36.4) | 6845 (36.1) | 20 138 (19.2) | 1095 (9.6) |
| >12 | 89 896 (49.2) | 9069 (47.8) | 61 255 (58.3) | 2878 (51.4) |
| Missing | 9559 (5.2) | 1581 (8.3) | 9975 (9.5) | 718 (12.8) |
| Income: | ||||
| Bottom third | 46 717 (25.6) | 3363 (17.7) | 45 898 (43.7) | 2758 (49.3) |
| Middle third | 46 548 (25.5) | 3531 (18.6) | 30 324 (28.9) | 1413 (25.3) |
| Top third | 46 859 (25.6) | 3220 (17.0) | 23 497 (22.4) | 1074 (19.2) |
| Missing | 40 387 (22.1) | 8700 (45.9) | 5371 (5.1) | 351 (6.3) |
| Birth region: | ||||
| Scandinavia | 126 378 (69.1) | 12 755 (67.3) | 78 400 (74.6) | 3613 (64.6) |
| Other European countries | 14 574 (8.0) | 1500 (7.9) | 11 728 (11.2) | 767 (13.7) |
| Middle East/Africa | 28 826 (15.8) | 3205 (16.9) | 6987 (6.7) | 764 (13.7) |
| Other | 8518 (4.7) | 661 (3.5) | 7960 (7.6) | 451 (8.1) |
| Missing | 4514 (2.5) | 839 (4.4) | 15 (0.01) | 1 (0.02) |
| Smoking status: | ||||
| Non-smoker | 170 485 (93.3) | 17 725 (93.5) | 89 050 (84.7) | 4678 (83.6) |
| Smoker | 6101 (3.3) | 533 (2.8) | 5269 (5.0) | 263 (4.7) |
| Missing | 6224 (3.4) | 702 (3.7) | 10 771 (10.3) | 655 (11.7) |
| Living with partner: | ||||
| Yes | 165 110 (90.3) | 17 337 (91.4) | 99 197 (94.4) | 5248 (93.8) |
| No | 13 727 (7.5) | 1270 (6.7) | 4153 (4.0) | 258 (4.6) |
| Missing | 3973 (2.2) | 353 (1.9) | 1740 (1.7) | 90 (1.6) |
| Coexisting medical conditions: | ||||
| Gestational diabetes | 8184 (4.5) | 846 (4.5) | 6802 (6.5) | 379 (6.8) |
| Pre-existing diabetes mellitus | 1994 (1.1) | 229 (1.2) | 790 (0.8) | 31 (0.6) |
| Chronic kidney disease | 645 (0.4) | 66 (0.3) | 575 (0.6) | 33 (0.6) |
| Systemic lupus erythematosus | 259 (0.1) | 30 (0.2) | 88 (0.1) | 2 (0.04) |
| History of hypertension during pregnancy: | ||||
| Yes | 1413 (0.8) | 112 (0.6) | 3517 (3.4) | 199 (3.6) |
| Missing | 40 387 (22.1) | 8700 (45.9) | 0 | 0 |
| No of visits to outpatient care one year before conception: | ||||
| 0 | 87 900 (48.1) | 6232 (32.9) | n/a | n/a |
| 1-9 | 51 839 (28.4) | 3859 (20.4) | n/a | n/a |
| 10-29 | 2637 (1.4) | 164 (0.9) | n/a | n/a |
| ≥30 | 47 (0.0) | 5 (0.0) | n/a | n/a |
| Missing | 40 387 (22.1) | 8700 (45.9) | 105 090 (100.0) | 5596 (100.0) |
| Gestational age at birth: | ||||
| Week 22+0 to 36+6 | 7686 (4.2) | 796 (4.2) | 4726 (4.5) | 195 (3.5) |
| Week 37+0 to 39+6 | 83 388 (45.6) | 8789 (46.4) | 43 972 (41.8) | 2415 (43.2) |
| Week ≥40+0 | 91 736 (50.2) | 9375 (49.4) | 56 392 (53.7) | 2986 (53.4) |
Data are numbers (percentages).
*A missing indicator was used in adjusted analyses for body mass index, education, income, birth region, smoking status, history of hypertension during pregnancy, and visits to outpatient care.