Table. Maternal, Pregnancy, and Birth Characteristics by SARS-CoV-2 Test Positivity in Pregnant Women.
| Characteristics | Maternal SARS-CoV-2 test status | ||||
|---|---|---|---|---|---|
| Positive test result | No positive test result (full cohort) | Standardized differencea | No positive test result (matched cohort)b | Standardized differencea | |
| No. of mothersc | 2286 | 84 719 | 9137 | ||
| No. of infantsc | 2323 | 85 836 | 9275 | ||
| Maternal age at delivery, y | |||||
| Mean (SD) | 31.4 (5.0) | 31.4 (4.9) | 0.003 | 31.5 (4.9) | −0.009 |
| Median (IQR) [range] | 31.3 (28.0-34.8) [17.3 to 49.8] | 31.3 (28.2-34.7) [14.1 to 59.9] | 31.3 (28.1-34.8) [16.6 to 52.0] | ||
| No. (%) | |||||
| 13-24 | 224 (9.6) | 7672 (8.9) | 0.024 | 865 (9.3) | 0.011 |
| 25-29 | 689 (29.7) | 25 926 (30.2) | −0.012 | 2734 (29.5) | 0.004 |
| 30-34 | 855 (36.8) | 32 343 (37.7) | −0.018 | 3437 (37.1) | −0.005 |
| ≥35 | 555 (23.9) | 19 886 (23.2) | 0.017 | 2239 (24.1) | −0.006 |
| Missing data | 0 | 9 | −0.014 | 0 | 0 |
| Parity, No. (%) | |||||
| Nulliparous | 1001 (43.1) | 37 058 (43.2) | −0.002 | 3995 (43.1) | 0.000 |
| Multiparous | 1321 (56.9) | 48 740 (56.8) | 0.002 | 5278 (56.9) | −0.001 |
| Missing data | 1 | 38 | −0.001 | 2 | 0.012 |
| Singletons, No. (%) | 2247 (96.7) | 83 532 (97.3) | −0.035 | 8988 (96.9) | −0.010 |
| Multiple pregnancy, No. (%) | 76 (3.3) | 2304 (2.7) | 0.035 | 287 (3.1) | 0.010 |
| Prepregnancy comorbidity, No. (%)d | 231 (9.9) | 8581 (10.0) | −0.002 | 850 (9.2) | 0.027 |
| Gestational diabetes, No. (%) | 163 (7.0) | 4331 (5.0) | 0.083 | 592 (6.4) | 0.025 |
| Body mass indexe | |||||
| Mean (SD) | 26.0 (5.2) | 25.3 (5.0) | 0.132 | 25.9 (5.3) | 0.020 |
| Median (IQR) [range] | 24.9 (22.3-28.9) [14.5 to 55.7] | 24.2 (21.8-27.8) [13.2 to 69.8] | 24.8 (22.1-28.7) [14.7 to 54.6] | ||
| No. (%) | |||||
| <18.5 | 36 (1.6) | 1949 (2.4) | −0.053 | 151 (1.7) | −0.006 |
| 18.5 to <25 | 1092 (48.7) | 44 481 (54.1) | −0.096 | 4433 (49.6) | −0.016 |
| 25 to <30 | 661 (29.5) | 22 558 (27.5) | 0.049 | 2615 (29.2) | 0.006 |
| 30 to <35 | 309 (13.8) | 8998 (10.9) | 0.087 | 1155 (12.9) | 0.025 |
| ≥35 | 144 (6.4) | 4190 (5.1) | 0.058 | 591 (6.6) | −0.007 |
| Missing data | 81 | 3660 | −0.040 | 330 | −0.004 |
| Educational level, No. (%), y | |||||
| ≤9 | 207 (10.8) | 5616 (7.9) | 0.089 | 761 (10.0) | 0.025 |
| 10-12 | 656 (34.2) | 25 090 (35.3) | −0.022 | 2632 (34.5) | −0.003 |
| >12 | 1053 (55.0) | 40 287 (56.7) | −0.032 | 4241 (55.6) | −0.008 |
| Missing data | 407 | 14 843 | 0.006 | 1641 | −0.005 |
| Smoking status, No. (%) | |||||
| Nonsmoker | 2201 (97.6) | 79 820 (96.3) | 0.073 | 8887 (97.9) | −0.050 |
| Smoker | 55 (2.4) | 3048 (3.7) | −0.070 | 195 (2.1) | 0.018 |
| Missing data | 67 | 2968 | −0.033 | 193 | 0.052 |
| Birth country, No. (%) | |||||
| Nordic | 1320 (62.6) | 56 127 (71.9) | −0.176 | 5345 (63.6) | −0.016 |
| Non-Nordic Europe | 152 (7.2) | 5546 (7.1) | 0.003 | 591 (7.0) | 0.007 |
| Middle East/Africa | 536 (25.4) | 12 429 (15.9) | 0.221 | 2142 (25.5) | 0.000 |
| Other | 99 (4.7) | 3977 (5.1) | −0.018 | 332 (3.9) | 0.035 |
| Missing data | 216 | 7757 | 0.009 | 865 | −0.001 |
| Living with partner, No. (%) | |||||
| Yes | 2101 (91.8) | 77 263 (91.7) | 0.015 | 8412 (92.0) | −0.009 |
| No | 187 (8.2) | 6980 (8.3) | −0.003 | 736 (8.0) | 0.004 |
| Missing data | 35 | 1593 | −0.027 | 127 | 0.012 |
| Health care region, No. (%) | |||||
| North | 117 (5.0) | 5536 (6.4) | −0.061 | 460 (5.0) | 0.004 |
| Middle | 378 (16.3) | 12 516 (14.6) | 0.047 | 1512 (16.3) | −0.001 |
| East | 850 (36.6) | 24 176 (28.2) | 0.181 | 3393 (36.6) | 0.000 |
| West | 468 (20.1) | 19 473 (22.7) | −0.062 | 1872 (20.2) | −0.001 |
| Southeast | 231 (9.9) | 9802 (11.4) | −0.048 | 924 (10.0) | −0.001 |
| South | 279 (12.0) | 14 332 (16.7) | −0.134 | 1114 (12.0) | 0.000 |
| Delivery hospital, No. (%) | |||||
| Hospital with full neonatal intensive care unit | 838 (36.1) | 24 778 (28.9) | 0.154 | 2724 (29.4) | 0.143 |
| Other unit | 1485 (63.9) | 61 058 (71.1) | −0.154 | 6551 (70.6) | −0.143 |
| Antenatal corticosteroids administered because of preterm birth, No. (%) | 58 (2.5) | 1061 (1.2) | 0.193 | 104 (1.1) | 0.103 |
| Onset of delivery, No. (%) | |||||
| Spontaneous | 1490 (64.1) | 55 662 (64.8) | −0.015 | 6033 (65.0) | −0.019 |
| Induction of labor | 563 (24.2) | 21 857 (25.5) | −0.028 | 2258 (24.3) | −0.003 |
| Cesarean delivery | 270 (11.6) | 8317 (9.7) | 0.063 | 984 (10.6) | 0.032 |
| Mode of delivery, No. (%) | |||||
| Vaginal birth | 1828 (78.7) | 70 386 (82.0) | −0.083 | 7525 (81.1) | −0.061 |
| Cesarean delivery | 495 (21.3) | 15 450 (18.0) | 0.083 | 1750 (18.9) | 0.061 |
| Time from date of positive maternal SARS-CoV-2 test result to birth, d | |||||
| Mean (SD) | 56.3 (62.6) | ||||
| Median (IQR) [range] | 36 (5-85) [−7 to 284] | ||||
| Infant sex, No. (%) | |||||
| Male | 1157 (49.8) | 43 839 (51.1) | −0.025 | 4776 (51.5) | −0.034 |
| Female | 1166 (50.2) | 41 997 (48.9) | 0.025 | 4499 (48.5) | 0.034 |
| Gestational age | |||||
| Mean (SD), d | 274.7 (15.1) | 277.0 (12.6) | −0.162 | 277.1 (12.6) | −0.170 |
| Median (IQR) [range], d | 278 (270-284) [157 to 296] | 279 (272-285) [154 to 305] | 279 (272-285) [159 to 302] | ||
| No. (%), wk | |||||
| 22 to <32 | 38 (1.6) | 675 (0.8) | 0.078 | 66 (0.7) | 0.086 |
| 32 to <35 | 90 (3.9) | 1742 (2.0) | 0.109 | 177 (1.9) | 0.118 |
| 35 to <42 | 2194 (94.4) | 82 052 (95.6) | −0.053 | 8830 (95.2) | −0.034 |
| ≥42 | 39 (1.7) | 2042 (2.4) | −0.050 | 268 (2.9) | −0.081 |
| Apgar score at 5 min, No. (%) | |||||
| <7 | 48 (2.1) | 1300 (1.5) | 0.042 | 134 (1.5) | 0.047 |
| <4 | 9 (0.4) | 248 (0.3) | 0.017 | 29 (0.3) | 0.013 |
| Missing data | 32 | 601 | 0.067 | 52 | 0.083 |
| Birth weight, g | |||||
| Mean (SD) | 3436 (628) | 3502 (559) | −0.111 | 3495 (558) | −0.099 |
| Median (IQR) [range] | 3485 (3100-3826) [540 to 5860] | 3522 (3185-3855) [360 to 6040] | 3525 (3190-3840) [505 to 5800] | ||
| No. (%) | |||||
| Large for gestational age | 84 (3.7) | 3144 (3.7) | −0.002 | 328 (3.5) | 0.004 |
| Small for gestational age | 54 (2.4) | 1864 (2.2) | 0.010 | 246 (2.7) | −0.021 |
| Missing data | 52 | 799 | 0.105 | 31 | 0.170 |
Abbreviation: IQR, interquartile range.
a
Standardized differences were calculated according to Austin.30
b
Ten exposed infants (all twins) were not possible to match in a 1:4 ratio.
c
Numbers of mothers and infants differ because of multiple births.
d
Prepregnancy comorbidity included diabetes, hypertension, cardiovascular disease, kidney disease, and lung disease.
e
Body mass index is calculated as weight in kilograms divided by height in meters squared.