Table 1. General characteristics of the study population.
| Assisted Reproductive Technology | ||||||||
|---|---|---|---|---|---|---|---|---|
| Non-ART | IUI | IVF-ET | Total | |||||
| N | (%) | N | (%) | N | (%) | N | (%) | |
| Outcome: | ||||||||
| SMM | ||||||||
| No | 265,824 | (97.9) | 1,649 | (95.8) | 6,806 | (93.8) | 274,279 | (97.7) |
| Yes | 5,812 | (2.1) | 73 | (4.2) | 448 | (6.2) | 6,333 | (2.3) |
| Confounders: | ||||||||
| Maternal age (year) | ||||||||
| < 35 | 177,756 | (65.4) | 919 | (53.4) | 2,657 | (36.6) | 181,332 | (64.6) |
| 35–39 | 93,431 | (34.4) | 803 | (46.6) | 4,577 | (63.1) | 98,811 | (35.2) |
| 40 + | 449 | (0.2) | - | (0.0) | 20 | (0.3) | 469 | (0.2) |
| Income level | ||||||||
| Q1 | 55,823 | (20.6) | 266 | (15.5) | 1,324 | (18.3) | 57,413 | (20.5) |
| Q2 | 61,058 | (22.5) | 277 | (16.1) | 1,066 | (14.7) | 62,401 | (22.2) |
| Q3 | 96,333 | (35.5) | 670 | (38.9) | 2,498 | (34.4) | 99,501 | (35.5) |
| Q4 | 58,422 | (21.5) | 509 | (29.6) | 2,366 | (32.6) | 61,297 | (21.8) |
| Type of insurance | ||||||||
| Self-employed | 54,681 | (20.1) | 211 | (12.3) | 1,044 | (14.4) | 55,936 | (19.9) |
| Employees | 214,921 | (79.1) | 1,509 | (87.6) | 6,194 | (85.4) | 222,624 | (79.3) |
| Medical aids | 2,034 | (0.8) | 2 | (0.1) | 16 | (0.2) | 2,052 | (0.7) |
| Residential area | ||||||||
| Seoul | 50,293 | (18.5) | 408 | (23.7) | 1,734 | (23.9) | 52,435 | (18.7) |
| Metropolitan | 70,535 | (26.0) | 456 | (26.5) | 1,936 | (26.7) | 72,927 | (26.0) |
| Small cities | 136,430 | (50.2) | 808 | (46.9) | 3,297 | (45.5) | 140,535 | (50.1) |
| Rural | 14,378 | (5.3) | 50 | (2.9) | 287 | (4.0) | 14,715 | (5.2) |
| Mode of delivery | ||||||||
| Vaginal | 64,639 | (23.8) | 284 | (16.5) | 832 | (11.5) | 65,755 | (23.4) |
| Instrumental | 85,074 | (31.3) | 451 | (26.2) | 1,441 | (19.9) | 86,966 | (31.0) |
| Cesarean section | 121,923 | (44.9) | 987 | (57.3) | 4,981 | (68.7) | 127,891 | (45.6) |
| Preterm birth | ||||||||
| No | 262,624 | (96.7) | 1,571 | (91.2) | 6,557 | (90.4) | 270,752 | (96.5) |
| Yes | 9,012 | (3.3) | 151 | (8.8) | 697 | (9.6) | 9,860 | (3.5) |
| Prenatal care | ||||||||
| Adequacy | 264,571 | (97.4) | 1,721 | (99.9) | 7,254 | (100.0) | 273,546 | (97.5) |
| Intermediate | 6,320 | (2.3) | 1 | (0.1) | - | (0.0) | 6,321 | (2.3) |
| Inadequacy | 745 | (0.3) | - | (0.0) | - | (0.0) | 745 | (0.3) |
| Parity | ||||||||
| Nulliparous | 140,917 | (51.9) | 1,369 | (79.5) | 5,759 | (79.4) | 148,045 | (52.8) |
| Multiparous | 130,719 | (48.1) | 353 | (20.5) | 1,495 | (20.6) | 132,567 | (47.2) |
| Twin birth status | ||||||||
| Singleton | 268,062 | (98.7) | 1,425 | (82.8) | 5,784 | (79.7) | 275,271 | (98.1) |
| Twin | 3,574 | (1.3) | 297 | (17.3) | 1,470 | (20.3) | 5,341 | (1.9) |
| Comorbidities during pregnancy | ||||||||
| 0 | 101,310 | (37.3) | 500 | (29.0) | 2,152 | (29.7) | 103,962 | (37.1) |
| 1+ | 170,326 | (62.7) | 1,222 | (71.0) | 5,102 | (70.3) | 176,650 | (63.0) |
| Type of hospital (No. of beds) | ||||||||
| General hospital (500+) | 16,077 | (5.9) | 297 | (17.3) | 1,441 | (19.9) | 17,815 | (6.4) |
| Hospital (100–499) | 19,952 | (7.4) | 218 | (12.7) | 1,140 | (15.7) | 21,310 | (7.6) |
| Hospital (30–99) | 139,580 | (51.4) | 839 | (48.7) | 3,284 | (45.3) | 143,703 | (51.2) |
| Clinic (29 and less) | 96,027 | (35.4) | 368 | (21.4) | 1,389 | (19.2) | 97,784 | (34.9) |
Abbreviations: ART, assisted reproductive technology; IUI, intrauterine insemination; IVF-ET, in vitro fertilization and embryo transfer; SMM, severe maternal morbidity