Table 3.
Associations of exposure to the COVID-19 lockdown with preterm birth
| Unexposed group (n, %) | Exposed group (n, %) a | OR for PTB (95%CI) | ||||||||||||
| Term birth | PTB | Term birth | PTB | MPTB + VPTB | MPTB | VPTB | ||||||||
| MPTB + VPTB | MPTB | VPTB | MPTB + VPTB | MPTB | VPTB | Crude OR | Adjusted OR * | Crude OR | Adjusted OR * | Crude OR | Adjusted OR * | |||
| Gestational week at the beginning of the Level I lockdown | ||||||||||||||
| All | 451,284 (94.7) | 25,631 (5.3) | 23,510 (4.9) | 2121 (0.4) | 92,669 (94.3) | 5593 (5.7) | 5150 (5.2) | 443 (0.5) | 1.06 (1.03, 1.09) | 1.08 (1.05, 1.11) | 1.07 (1.03, 1.10) | 1.09 (1.05, 1.12) | 1.02 (0.92, 1.13) | 1.04 (0.94, 1.16) |
| Conception during the lockdown | 61,117 (94.5) | 3528 (5.5) | 3171 (4.9) | 357 (0.6) | 10,682 (94.4) | 635 (5.6) | 573 (5.1) | 62 (0.5) | 1.03 (0.94, 1.12) | 1.09 (0.99, 1.20) | 1.03 (0.94, 1.13) | 1.08 (0.98, 1.19) | 0.99 (0.76, 1.30) | 1.20 (0.90, 1.61) |
| Prior to 4th | 50,272 (94.3) | 3028 (5.7) | 2746 (5.2) | 282 (0.5) | 10,295 (94.1) | 642 (5.9) | 591 (5.4) | 51 (0.5) | 1.04 (0.95, 1.13) | 1.18 (1.08, 1.29) | 1.05 (0.96, 1.15) | 1.20 (1.09, 1.32) | 0.88 (0.65, 1.19) | 0.97 (0.71, 1.32) |
| 4th -7th | 48,023 (94.3) | 2950 (5.7) | 2671 (5.2) | 279 (0.5) | 9821 (93.6) | 673 (6.4) | 613 (5.8) | 60 (0.6) | 1.12 (1.02, 1.22) | 1.12 (1.03, 1.22) | 1.12 (1.03, 1.23) | 1.13 (1.03, 1.24) | 1.05 (0.79, 1.39) | 1.07 (0.81, 1.42) |
| 8th -11th | 46,128 (94.3) | 2798 (5.7) | 2544 (5.2) | 254 (0.5) | 9581 (93.6) | 656 (6.4) | 597 (5.8) | 59 (0.6) | 1.13 (1.03, 1.23) | 1.14 (1.04, 1.24) | 1.13 (1.03, 1.24) | 1.14 (1.04, 1.25) | 1.12 (0.84, 1.49) | 1.13 (0.85, 1.51) |
| 12th -15th | 43,652 (94.4) | 2603 (5.6) | 2356 (5.1) | 247 (0.5) | 9236 (93.9) | 608 (6.1) | 546 (5.5) | 62 (0.6) | 1.10 (1.01, 1.21) | 1.11 (1.02, 1.22) | 1.10 (1.00, 1.21) | 1.10 (1.00, 1.21) | 1.19 (0.90, 1.57) | 1.21 (0.91, 1.59) |
| 16th -19th | 43,439 (94.6) | 2474 (5.4) | 2252 (4.9) | 222 (0.5) | 8966 (94.0) | 573 (6.0) | 524 (5.5) | 49 (0.5) | 1.12 (1.02, 1.23) | 1.14 (1.04, 1.25) | 1.13 (1.02, 1.24) | 1.14 (1.04, 1.26) | 1.07 (0.78, 1.46) | 1.11 (0.82, 1.52) |
| 20th -23rd | 38,806 (94.6) | 2211 (5.4) | 2011 (4.9) | 200 (0.5) | 8281 (93.8) | 549 (6.2) | 502 (5.7) | 47 (0.5) | 1.16 (1.06, 1.28) | 1.19 (1.08, 1.31) | 1.17 (1.06, 1.29) | 1.19 (1.08, 1.32) | 1.10 (0.80, 1.51) | 1.14 (0.83, 1.57) |
| 24th -27th | 38,052 (94.3) | 2306 (5.7) | 2112 (5.2) | 194 (0.5) | 8291 (94.8) | 459 (5.2) | 420 (4.8) | 39 (0.4) | 0.91 (0.82, 1.01) | 0.93 (0.84, 1.03) | 0.91 (0.82, 1.02) | 0.93 (0.83, 1.03) | 0.92 (0.65, 1.30) | 0.99 (0.70, 1.40) |
| 28th -31st | 36,145 (94.8) | 2001 (5.2) | 1915 (5.0) | 86 (0.2) | 7663 (94.6) | 438 (5.4) | 424 (5.2) | 14 (0.2) | 1.03 (0.93, 1.15) | 1.05 (0.95, 1.17) | 1.04 (0.94, 1.16) | 1.06 (0.95, 1.19) | 0.77 (0.44, 1.35) | 0.80 (0.45, 1.42) |
| 32nd -36th | 45,650 (96.3) | 1732 (3.7) | 1732 (3.7) | NA | 9853 (96.5) | 360 (3.5) | 360 (3.5) | NA | 0.96 (0.86, 1.08) | 0.97 (0.86, 1.09) | 0.96 (0.86, 1.08) | 0.97 (0.86, 1.09) | NA | NA |
|
Exposure dose in unexposed group (Mean ± SD) |
Exposure dose in exposed group (Mean ± SD) |
OR for PTB (95%CI) | ||||||||||||
| Term + PTB | Term | PTB | MPTB + VPTB | MPTB | VPTB | |||||||||
| MPTB + VPTB | MPTB | VPTB | Crude OR | Adjusted OR* | Crude OR | Adjusted OR* | Crude OR | Adjusted OR* | ||||||
| Cumulative exposure dose in the first 22 weeks during Level I to Level 3 lockdown b | ||||||||||||||
| Per 100 unit increase | 0 ± 0 | 195.14 ± 82.19 | 194.15 ± 82.57 | 194.23 ± 82.60 | 193.35 ± 82.38 | 1.06 (1.04, 1.08) | 1.07 (1.05, 1.09) | 1.05 (1.04 1.07) | 1.07 (1.05, 1.08) | 1.10 (1.05, 1.16) | 1.12 (1.06, 1.18) | |||
| Categories of cumulative exposure dose | ||||||||||||||
| Unexposed group | 0 ± 0 | – | Reference | Reference | Reference | Reference | Reference | Reference | ||||||
| Q1 (< 132) | – | 73.52 ± 38.09 | 71.59 ± 38.28 | 71.49 ± 38.32 | 72.57 ± 38.07 | 1.14 (1.07, 1.22) | 1.16 (1.08, 1.23) | 1.13 (1.05, 1.21) | 1.14 (1.07, 1.22) | 1.27 (1.03, 1.67) | 1.31 (1.06, 1.62) | |||
| Q2 (132–225) | – | 178.64 ± 27.17 | 179.01 ± 27.26 | 179.14 ± 27.26 | 177.76 ± 27.29 | 1.21 (1.13, 1.29) | 1.22 (1.14, 1.30) | 1.19 (1.11, 1.27) | 1.20 (1.12, 1.28) | 1.39 (1.14, 1.70) | 1.43 (1.17, 1.74) | |||
| Q3 (226–263) | – | 247.16 ± 10.59 | 247.52 ± 10.28 | 247.50 ± 10.26 | 247.91 ± 10.58 | 1.11 (1.04 1.19) | 1.14 (1.07, 1.22) | 1.10 (1.03, 1.18) | 1.13 (1.05, 1.21) | 1.25 (1.01, 1.54) | 1.27 (1.03, 1.58) | |||
| Q4 (≥264) | – | 278.81 ± 8.57 | 278.69 ± 8.77 | 278.55 ± 8.76 | 280.23 ± 8.79 | 1.14 (1.06, 1.21) | 1.19 (1.11, 1.27) | 1.13 (1.05, 1.21) | 1.18 (1.10, 1.26) | 1.21 (0.97, 1.49) | 1.25 (1.01, 1.55) | |||
| P for trend test | < 0.001 | < 0.001 | < 0.001 | |||||||||||
In calculating the cumulative exposure dose to lockdown, we assigned a weighting of 3 to days with Level I response, 2 to days with Level II response, 1 to days with Level III response, and 0 to other days
PTB preterm birth, MPTB moderate preterm birth, VPTB very preterm birth
N/A: There is no VPTB case in the subgroup
*: Adjusted for maternal age, marital status, parity, residential city, delivery type and infant sex
a Pregnant women who have experienced the COVID-19 lockdown (from 1/23/2020 to 2/24/2020) during any period of their pregnancy were defined as the exposed group. We further divided the exposed group into subgroups. According to their gestational weeks (GW) on 1/23/2020, the beginning of lockdown
b: The exposed group refers to the pregnant women who have experienced the COVID-19 lockdown in their first 22 GWs. The rest of included participants were defined as the unexposed group. The individual cumulative exposure dose was calculated by combining the weightings with the overlap between their pregnancy period ≤22 GWs and the three levels of responses. Q1-Q4 were defined as the cumulative exposure dose of the exposed group classified by quartiles, and the unexposed group were used as reference
-: Not applicable