Table 1.
Baseline characteristics of study subjects from 2010 to 2017
| Characteristics | Full unmatched cohort (n=3 128 571)* | Propensity score matched cohort A (n=1 291 412)† | Standardised mean difference‡ | |||
|---|---|---|---|---|---|---|
| Children with prenatal opioid exposure | Children without prenatal exposure | Children with prenatal opioid exposure | Children without prenatal exposure | |||
| Total, no | 216 012 | 2 912 559 | 215 958 | 1 075 454 | — | |
| Matching variables | ||||||
| Maternal characteristics: | ||||||
| Maternal age at delivery year, mean (SD) | 32.3 (4.2) | 31.9 (4.2) | 32.3 (4.2) | 32.3 (4.1) | 0.01 | |
| Maternal age at delivery year, no (%) | <0.01 | |||||
| ≤19 | 545 (0.3) | 7330 (0.3) | 545 (0.3) | 2558 (0.2) | ||
| 20-24 | 7992 (3.7) | 128 697 (4.4) | 7991 (3.7) | 39 487 (3.7) | ||
| 25-29 | 41 094 (19.0) | 633 948 (21.8) | 41 090 (19.0) | 204 847 (19.1) | ||
| 30-34 | 102 874 (47.6) | 1 393 988 (47.9) | 102 855 (47.6) | 512 850 (47.7) | ||
| ≥35 | 63 507 (29.4) | 748 596 (25.7) | 63 477 (29.4) | 315 712 (29.4) | ||
| Region of residence, no (%) | <0.01 | |||||
| Rural | 90 163 (41.7) | 1 262 028 (43.3) | 90 146 (41.7) | 449 082 (41.8) | ||
| Urban | 125 849 (58.3) | 1 650 531 (56.7) | 125 812 (58.3) | 626 372 (58.2) | ||
| Income level, no (%) | <0.01 | |||||
| 1st quartile | 50 684 (23.5) | 649 207 (22.3) | 50 664 (23.5) | 251 255 (23.4) | ||
| 2nd quartile | 55 788 (25.8) | 750 159 (25.8) | 55 775 (25.8) | 277 762 (25.8) | ||
| 3rd quartile | 54 441 (25.2) | 733 069 (25.2) | 54 428 (25.2) | 271 342 (25.2) | ||
| 4th quartile | 55 099 (25.5) | 780 124 (26.8) | 55 091 (25.5) | 275 095 (25.6) | ||
| Parity, no (%) | <0.01 | |||||
| 1 | 181 261 (83.9) | 2 217 878 (76.2) | 181 212 (83.9) | 902 974 (84.0) | ||
| ≥2 | 34 751 (16.1) | 694 681 (23.9) | 34 746 (16.1) | 172 480 (16.0) | ||
| Maternal medical conditions, no (%) | 0.01 | |||||
| No mental illness | 168 482 (78.0) | 2 473 110 (84.9) | 168 481 (78.0) | 842 539 (78.3) | ||
| Common | 42 533 (19.7) | 398 371 (13.7) | 42 513 (19.7) | 210 059 (19.5) | ||
| Severe | 4997 (2.3) | 41 078 (1.4) | 4964 (2.3) | 22 856 (2.1) | ||
| Severe maternal morbidity, no (%) | <0.01 | |||||
| 0 | 198 017 (91.7) | 2 731 862 (93.8) | 198 009 (91.7) | 988 081 (91.9) | ||
| 1 | 17 332 (8.0) | 175 983 (6.0) | 17 306 (8.0) | 84 666 (7.9) | ||
| ≥2 | 663 (0.3) | 4714 (0.2) | 643 (0.3) | 2707 (0.3) | ||
| No of hospital admissions in a year before pregnancy, no (%) | <0.01 | |||||
| 0 | 171 976 (79.6) | 2 468 433 (84.8) | 171 966 (79.6) | 859 082 (79.9) | ||
| 1 | 35 213 (16.3) | 370 988 (12.7) | 35 203 (16.3) | 174 627 (16.2) | ||
| ≥2 | 8823 (4.1) | 73 138 (2.5) | 8789 (4.1) | 41 745 (3.9) | ||
| No of outpatient contacts in a year before pregnancy, no (%) | <0.01 | |||||
| 0 | 4619 (2.1) | 188 625 (6.5) | 4616 (2.1) | 23 009 (2.1) | ||
| 1 | 4890 (2.3) | 162 503 (5.6) | 4890 (2.3) | 24 369 (2.3) | ||
| ≥2 | 206 503 (95.6) | 2 561 431 (87.9) | 206 452 (95.6) | 1 028 076 (95.6) | ||
| Alcohol or drug misuse, no (%) | 558 (0.3) | 3920 (0.1) | 540 (0.3) | 1980 (0.2) | 0.01 | |
| Mood disorders except those with psychotic symptoms, no (%) | 9699 (4.5) | 74 053 (2.5) | 9658 (4.5) | 45 415 (4.2) | 0.01 | |
| Anxiety and stress-related disorders, no (%) | 16 195 (7.5) | 129 873 (4.5) | 16 150 (7.5) | 77 673 (7.2) | 0.01 | |
| Sleep disorders, no (%) | 8392 (3.9) | 59 394 (2.0) | 8347 (3.9) | 38 962 (3.6) | 0.01 | |
| Epilepsy, no (%) | 884 (0.4) | 8696 (0.3) | 870 (0.4) | 3691 (0.3) | 0.01 | |
| Other neuropsychiatry disorders, no (%) | 814 (0.4) | 6713 (0.2) | 805 (0.4) | 3369 (0.3) | 0.01 | |
| Unmatching variables | ||||||
| Delivery type, no (%): | 0.16 | |||||
| Vaginal delivery | 115 193 (53.3) | 1 693 716 (58.2) | 115 174 (53.3) | 659 523 (61.3) | ||
| Caesarean section | 100 819 (46.7) | 1 218 843 (41.9) | 100 784 (46.7) | 415 931 (38.7) | ||
| Use of NSAIDs during pregnancy, no (%) | 103 912 (48.1) | 482 329 (16.6) | 103 877 (48.1) | 204 829 (19.1) | 0.65 | |
| Use of acetaminophen during pregnancy, no (%) | 148 024 (68.5) | 789 528 (27.1) | 147 981 (68.5) | 328 716 (30.6) | 0.82 | |
| Infant characteristics: | ||||||
| Infant sex, no (%) | <0.01 | |||||
| Male | 110 511 (51.2) | 1 495 374 (51.3) | 110 487 (51.2) | 551 281 (51.3) | ||
| Female | 105 501 (48.8) | 1 417 185 (48.7) | 105 471 (48.8) | 524 173 (48.7) | ||
| Birth season, no (%) | 0.07 | |||||
| Spring | 53 228 (24.6) | 756 304 (26.0) | 53 214 (24.6) | 279 000 (25.9) | ||
| Summer | 58 458 (27.1) | 708 808 (24.3) | 58 434 (27.1) | 261 523 (24.3) | ||
| Autumn | 51 697 (23.9) | 718 496 (24.7) | 51 687 (23.9) | 268 571 (25.0) | ||
| Winter | 52 629 (24.4) | 728 951 (25.0) | 52 623 (24.4) | 266 360 (24.8) | ||
| Year of delivery, no (%) | 0.11 | |||||
| 2010 to 2012 | 69 885 (32.4) | 1 119 845 (38.5) | 69 874 (32.4) | 400 367 (37.2) | ||
| 2013 to 2015 | 76 973 (35.6) | 997 353 (34.2) | 76 952 (35.6) | 378 610 (35.2) | ||
| 2016 to 2017 | 69 154 (32.0) | 795 361 (27.3) | 69 132 (32.0) | 296 477 (27.6) | ||
| At-risk newborn, no (%) | 0.07 |
|||||
| Preterm birth | 10 817 (5.0) | 103 949 (3.6) | 203 182 (94.1) | 1 028 054 (95.6) | ||
| Low birth weight | 7860 (3.6) | 83 354 (2.9) | 12 776 (5.9) | 47 400 (4.4) | ||
NSAIDs=non-steroidal anti-inflammatory drugs; SD=standard deviation.
*
Full unmatched cohort involves infants born between 2010 and 2017 (cohort 1 in fig 1 and table S8).
†
Propensity score matched cohort A, derived from the full unmatched cohort, involves a 1:5 matching ratio and pairs the exposed and unexposed groups in a 1:5 ratio using propensity score (cohort 2 in fig 1 and table S8).
‡
Standardised mean difference of <0.1 corresponds to no major imbalance.