Hazard ratios for hypertension during pregnancy according to SARS-CoV-2 infection in different trimesters, time periods corresponding to the dominant variant of the virus, and vaccination status in Sweden and Norway
| SARS-CoV-2 infection | Patients (No (%)) | Follow-up time after infection (days) | Crude hazard ratio (95% CI) | Adjusted hazard ratio* (95% CI) |
| Sweden: hypertension during pregnancy | ||||
| No infection | 10 568 (5.8) | Reference | Reference | |
| Positive test result in: | ||||
| First trimester | 175 (5.4) | 347 634 | 0.98 (0.84 to 1.13) | 0.94 (0.81 to 1.10) |
| Second trimester | 364 (5.6) | 725 441 | 0.96 (0.86 to 1.07) | 0.97 (0.87 to 1.08) |
| Third trimester | 489 (5.3) | 349 640 | 1.01 (0.91 to 1.12) | 1.03 (0.93 to 1.15) |
| Index variant | 429 (6.5) | 651 148 | 1.09 (0.98 to 1.20) | 1.08 (0.98 to 1.20) |
| Alpha variant | 244 (5.0) | 355 105 | 0.93 (0.82 to 1.07) | 0.91 (0.79 to 1.04) |
| Delta variant | 73 (4.2) | 130 816 | 0.78 (0.61 to 0.99) | 0.86 (0.67 to 1.10) |
| Omicron variant | 282 (4.9) | 285 646 | 0.93 (0.81 to 1.07) | 0.97 (0.84 to 1.11) |
| At least one dose of vaccine before infection | 261 (5.4) | 272 427 | 1.03 (0.89 to 1.18) | 1.01 (0.87 to 1.16) |
| Not vaccinated | 767 (5.4) | 1 150 288 | 0.97 (0.90 to 1.05) | 0.98 (0.91 to 1.06) |
| Sweden: pre-eclampsia | ||||
| No infection | 5 376 (2.9) | Reference | Reference | |
| Positive test result in: | ||||
| First trimester | 90 (2.8) | 348 969 | 0.97 (0.78 to 1.20) | 0.93 (0.75 to 1.16) |
| Second trimester | 173 (2.7) | 728 416 | 0.91 (0.78 to 1.06) | 0.91 (0.78 to 1.06) |
| Third trimester | 237 (2.6) | 352 374 | 1.01 (0.87 to 1.18) | 1.05 (0.90 to 1.23) |
| Index variant | 231 (3.5) | 654 192 | 1.15 (1.00 to 1.33) | 1.13 (0.98 to 1.31) |
| Alpha variant | 120 (2.5) | 356 447 | 0.88 (0.73 to 1.07) | 0.86 (0.71 to 1.05) |
| Delta variant | 33 (1.9) | 131 436 | 0.73 (0.51 to 1.05) | 0.79 (0.55 to 1.14) |
| Omicron variant | 116 (2.0) | 287 684 | 0.81 (0.65 to 1.00) | 0.85 (0.68 to 1.06) |
| At least one dose of vaccine before infection | 107 (2.2) | 274 403 | 0.90 (0.72 to 1.12) | 0.92 (0.74 to 1.14) |
| Not vaccinated | 393 (2.8) | 1 155 356 | 0.98 (0.88 to 1.09) | 0.98 (0.88 to 1.10) |
| Norway: hypertension during pregnancy | ||||
| No infection | 6082 (5.5) | Reference | Reference | |
| Positive test result in: | ||||
| First trimester | 18 (4.2) | 59 065 | 0.66 (0.41 to 1.05) | 0.65 (0.40 to 1.08) |
| Second trimester | 69 (5.5) | 143 498 | 0.81 (0.63 to 1.03) | 0.97 (0.75 to 1.25) |
| Third trimester | 190 (5.3) | 144 182 | 0.90 (0.77 to 1.06) | 1.04 (0.89 to 1.23) |
| Index variant | 22 (3.9) | 58 534 | 0.71 (0.47 to 1.09) | 0.80 (0.52 to 1.24) |
| Alpha variant | 24 (4.2) | 56 803 | 0.80 (0.53 to 1.20) | 0.95 (0.63 to 1.43) |
| Delta variant | 60 (5.2) | 97 198 | 0.81 (0.63 to 1.06) | 0.92 (0.71 to 1.21) |
| Omicron variant | 171 (5.8) | 134 210 | 0.92 (0.77 to 1.09) | 1.06 (0.89 to 1.27) |
| At least one dose of vaccine before infection | 169 (5.9) | 153 918 | 0.92 (0.77 to 1.09) | 1.01 (0.85 to 1.21) |
| Not vaccinated | 108 (4.3) | 192 827 | 0.79 (0.65 to 0.96) | 0.97 (0.79 to 1.18) |
| Norway: pre-eclampsia | ||||
| No infection | 3817 (3.5) | Reference | Reference | |
| Positive test result in: | ||||
| First trimester | 13 (3.0) | 59 077 | 0.80 (0.46 to 1.38) | 0.77 (0.42 to 1.40) |
| Second trimester | 43 (3.4) | 143 792 | 0.79 (0.58 to 1.08) | 0.94 (0.69 to 1.29) |
| Third trimester | 113 (3.1) | 144 880 | 0.90 (0.73 to 1.10) | 1.04 (0.84 to 1.28) |
| Index variant | 13 (2.3) | 58 677 | 0.69 (0.40 to 1.20) | 0.74 (0.42 to 1.32) |
| Alpha variant | 13 (2.3) | 56 825 | 0.69 (0.40 to 1.20) | 0.83 (0.48 to 1.44) |
| Delta variant | 41 (3.5) | 97 415 | 0.89 (0.65 to 1.22) | 0.99 (0.71 to 1.38) |
| Omicron variant | 102 (3.4) | 134 832 | 0.92 (0.73 to 1.16) | 1.08 (0.85 to 1.36) |
| At least one dose of vaccine before infection | 107 (3.7) | 154 563 | 0.98 (0.76 to 1.22) | 1.11 (0.89 to 1.38) |
| Not vaccinated | 62 (2.5) | 193 186 | 0.73 (0.57 to 0.95) | 0.87 (0.67 to 1.14) |
CI=confidence interval.
*Adjusted for maternal age, body mass index, parity, income, region of birth, educational level, smoking status, living with a partner, gestational and pre-existing diabetes, chronic kidney disease, systemic lupus erythematosus, history of hypertension during pregnancy, number of visits to an outpatient healthcare facility within one year of conception (Swedish data only), and vaccination against SARS-CoV-2.