Descriptive statistics
| Variables n (%) or m (IQR) | Overall | Low volume (1–18) | Medium volume (19–142) | High volume (143–5664) | P value |
| SMM n (%) | |||||
| No | 783 254 (96.69) | 9379 (98.23) | 95 436 (98.02) | 678 439 (96.49) | <0.001 *** |
| Yes | 26 795 (3.31) | 169 (1.77) | 1931 (1.98) | 24 695 (3.51) | |
| Delivery volume m (IQR) | 501 (260–893) | 11 (6–14) | 88 (19–114) | 584 (346–962) | <0.001 *** |
| Patient characteristics | |||||
| Age m (IQR) | 27 (24–30) | 27 (23–30) | 26 (23–30) | 27 (24–30) | <0.001 *** |
| Minority n (%) | |||||
| No | 721 177 (89.03) | 8567 (89.73) | 83 979 (86.25) | 628 631 (89.40) | <0.001 *** |
| Yes | 88 872 (10.97) | 981 (10.27) | 13 388 (13.75) | 74 503 (10.60) | |
| Married n (%) | |||||
| No | 32 551 (4.02) | 423 (4.43) | 4351 (4.47) | 27 777 (3.95) | <0.001 *** |
| Yes | 777 498 (95.98) | 9125 (95.57) | 930,16 (95.53) | 675 357 (96.05) | |
| Living in urban/rural n (%) | |||||
| Rural | 399 469 (49.31) | 5861 (61.38) | 59 572 (61.18) | 334 035 (47.51) | <0.001 *** |
| Urban | 410 581 (50.69) | 3687 (38.62) | 37 795 (38.82) | 369 099 (52.49) | |
| Insurance type n (%) | |||||
| UEBMI | 92 762 (11.45) | 302 (3.16) | 7942 (8.16) | 84 518 (12.02) | <0.001 *** |
| URBMI | 196 047 (24.20) | 3840 (40.22) | 29 804 (30.61) | 162 403 (23.10) | |
| NCMS | 247 315 (30.53) | 2978 (31.19) | 34 392 (35.32) | 209 945 (29.86) | |
| Fully self-paid | 176 960 (21.85) | 1343 (14.07) | 17 216 (17.68) | 158 401 (22.53) | |
| Others | 96 965 (11.97) | 1085 (11.36) | 8013 (8.23) | 87 867 (12.5) | |
| High-risk delivery n (%) | |||||
| No | 407 140 (50.26) | 7417 (77.68) | 61 019 (62.67) | 338 704 (48.17) | <0.001 *** |
| Yes | 402 909 (49.74) | 2131 (22.32) | 36 348 (37.33) | 364 430 (51.83) | |
| Admission source n (%) | |||||
| Transferred from the emergency department within the hospital | 156 324 (19.30) | 1040 (10.89) | 14 825 (15.23) | 140 459 (19.98) | <0.001 *** |
| Transferred from the outpatient department within the hospital | 631 184 (77.92) | 7841 (82.12) | 78 678 (80.81) | 544 665 (77.46) | |
| Transferred from other hospital | 2180 (0.27) | 14 (0.15) | 153 (0.16) | 2013 (0.29) | |
| Others | 20 361 (2.51) | 653 (6.84) | 3711 (3.81) | 15 997 (2.28) | |
| Institutional characteristics | |||||
| Hospital level n (%) | |||||
| Tertiary | 356 696 (44.03) | 117 (1.23) | 6981 (7.17) | 349 598 (49.72) | <0.001 *** |
| Secondary | 338 066 (41.73) | 1094 (11.46) | 42 418 (43.57) | 294 554 (41.89) | |
| Primary or ungraded | 115 287 (14.23) | 8337 (87.32) | 47 968 (49.27) | 58 982 (8.39) | |
| Location n (%) | |||||
| Rural | 351 502 (43.39) | 5902 (61.81) | 59 168 (60.77) | 286 432 (40.74) | <0.001 *** |
| Urban | 458 547 (56.61) | 3646 (38.19) | 38 199 (39.23) | 416 702 (59.26) | |
| Ownership and profit n (%) | |||||
| Public non-profit | 729 561 (90.06) | 7548 (79.05) | 78 255 (80.37) | 643 758 (91.56) | <0.001 *** |
| Private non-profit | 29 109 (3.59) | 632 (6.62) | 6305 (6.48) | 22 172 (3.15) | |
| Private for profit | 51 379 (6.34) | 1368 (14.33) | 12 807 (13.15) | 37 204 (5.29) | |
| Number of beds m (IQR) | 344 (129–800) | 80 (50–102) | 125 (70–250) | 409 (150–944) | <0.001 *** |
| Number of beds for OG m (IQR) | 53 (30–90) | 10 (5–15) | 20 (15–30) | 60 (38–95) | <0.001 *** |
| Regional characteristics | |||||
| GDP per capita m (IQR) | 37 589 (27 014–60 311) | 31 651 (23 020–42 642) | 33 666 (24 309–49 522) | 39 033 (27 539–62 208) | <0.001 *** |
| Urbanisation rate m (IQR) | 49.47 (39.03–71.75) | 40.75 (36.56–50.55) | 41.4 (36.81–53.31) | 51.48 (39.71–72.41) | <0.001 *** |
| Year n (%) | |||||
| 2016 | 230 700 (28.48) | 2308 (24.17) | 23 851 (24.5) | 204 541 (29.09) | <0.001 *** |
| 2017 | 208 263 (25.71) | 2637 (27.62) | 26 123 (26.83) | 179 503 (25.53) | |
| 2018 | 187 880 (23.19) | 2414 (25.28) | 24 561 (25.22) | 160 905 (22.88) | |
| 2019 | 183 206 (22.62) | 2189 (22.93) | 22 832 (23.45) | 158 185 (22.5) | |
| Number of delivery cases | 810 049 | 9548 | 97 367 | 703 134 |
The categorical variables were described by number and percentage ‘n (%)’, the continuous variables were described by median and IQR ‘m (IQR)’.
χ2 tests were employed for the categorical variables, Kruskal-Wallis rank-sum tests were employed for the continuous variables.
Significant: ‘***’p<0.001, ‘**’ p<0.01, ‘*’ p<0.05.
GDP per capita, gross domestic product per capita; NCMS, New Cooperative Medical Scheme; OG, Obstetrics and Gynecology; SMM, severe maternal morbidity; UEBMI, Urban Employment Basic Medical Insurance; URBMI, Urban Residents Basic Medical Insurance.