Table 1. Baseline characteristics of the cohort for the first live birth.
| Characteristic | Spontaneous Vaginal Delivery | Operative Vaginal Delivery | Emergency Cesarean Section | Elective Cesarean Section | Maternally Requested Cesarean Section* |
| Total | 607,252 (72.90) | 79,827 (9.58) | 104,091 (12.50) | 38,950 (4.68) | 2,876 (1.11) |
| Maternal age, years | |||||
| <20 | 21,883 (85.00) | 1,255 (4.87) | 1,994 (7.75) | 585 (2.27) | 28 (0.52) |
| 20–25 | 210,595 (80.08) | 17,828 (6.78) | 25,840 (9.83) | 8,356 (3.18) | 364 (0.68) |
| 26–30 | 245,579 (72.51) | 35,687 (10.54) | 41,448 (12.24) | 15,134 (4.47) | 812 (0.74) |
| 31–35 | 100,283 (64.74) | 18,995 (12.26) | 24,760 (15.98) | 9,888 (6.38) | 977 (1.46) |
| 36–40 | 25,427 (57.79) | 5,326 (12.10) | 8,574 (19.49) | 4,130 (9.39) | 545 (2.71) |
| 41+ | 3,485 (51.99) | 736 (10.98) | 1,475 (22.01) | 857 (12.79) | 150 (4.88) |
| Maternal origin | |||||
| Denmark | 527,328 (72.78) | 79,102 (9.68) | 90,540 (12.50) | 34,340 (4.74) | 2,249 (1.04) |
| Other | 78,003 (80.54) | 525 (0.54) | 13,243 (13.67) | 4,470 (4.62) | 615 (0.63) |
| Unknown | 1,921 (74.43) | 200 (7.75) | 308 (11.93) | 140 (5.42) | 12 (1.61) |
| Birth type | |||||
| Singleton | 601,111 (73.51) | 79,455 (9.72) | 98,972 (12.10) | 35,462 (4.34) | 2,700 (1.07) |
| Multiple (twins or more) | 6,141 (40.15) | 372 (2.43) | 5,119 (33.47) | 3,488 (22.80) | 176 (2.74) |
| Maternal smoking a | |||||
| Yes | 40,919 (68.51) | 6,971 (11.67) | 8,513 (14.25) | 2,966 (4.97) | 362 (1.13) |
| No | 211,833 (66.43) | 41,639 (13.06) | 46,472 (14.57) | 16,580 (5.20) | 2,343 (1.11) |
| Unknown | 17,722 (65.88) | 2,849 (10.59) | 4,509 (16.76) | 1,649 (6.13) | 171 (1.10) |
| Maternal BMI b (kg/m2) | |||||
| <18.5 | 9,673 (68.49) | 1,874 (13.27) | 1,609 (11.39) | 758 (5.37) | 209 (1.48) |
| 18.5–25 | 84,390 (65.12) | 17,379 (13.41) | 19,072 (14.72) | 7,092 (5.47) | 1,667 (1.29) |
| 26–30 | 17,482 (59.93) | 3,757 (12.88) | 5,812 (19.92) | 1,707 (5.85) | 414 (1.42) |
| 31–35 | 6,011 (57.59) | 1,199 (11.49) | 2,409 (23.08) | 662 (6.34) | 157 (1.50) |
| 36–40 | 1,877 (54.15) | 360 (10.39) | 930 (26.83) | 250 (7.21) | 49 (1.41) |
| 41+ | 827 (51.56) | 153 (9.54) | 472 (29.43) | 128 (7.98) | 24 (1.50) |
| Unknown | 27,950 (67.09) | 4,900 (11.76) | 6,218 (14.92) | 2,297 (5.51) | 298 (0.72) |
| Obstetric history c | |||||
| Previous stillbirth | 2,354 (58.38) | 130 (3.22) | 650 (16.12) | 826 (20.49) | 72 (6.09) |
| Previous miscarriage | 4,549 (64.36) | 783 (11.08) | 1,180 (16.69) | 521 (7.37) | 35 (1.51) |
| Previous ectopic pregnancy | 9,797 (65.76) | 1,588 (10.66) | 2,361 (15.85) | 1,066 (7.16) | 86 (1.75) |
| Mother's educational attainment | |||||
| Primary education | 164,565 (77.21) | 14,899 (6.99) | 24,502 (11.50) | 8,679 (4.07) | 501 (1.14) |
| High school | 278,573 (72.00) | 39,660 (10.25) | 49,058 (12.68) | 18,423 (4.76) | 1,178 (1.03) |
| Third level degree | 100,762 (69.73) | 16,054 (11.11) | 19,544 (13.53) | 7,551 (5.23) | 585 (0.99) |
| Masters/PhD | 31,386 (66.58) | 6,184 (13.12) | 6,469 (13.72) | 2,726 (5.78) | 377 (1.46) |
| Unknown | 31,966 (77.36) | 3,030 (7.33) | 4,518 (10.93) | 1,571 (3.80) | 235 (1.52) |
| Mother's gross income | |||||
| Highest quartile | 101,764 (68.19) | 16,644 (11.15) | 21,382 (14.33) | 8,669 (5.81) | 781 (1.46) |
| Second highest quartile | 266,390 (72.75) | 34,514 (9.43) | 46,978 (12.83) | 17,275 (4.72) | 1,000 (0.99) |
| Second lowest quartile | 121,491 (74.01) | 15,421 (9.39) | 19,409 (11.82) | 7,243 (4.41) | 583 (1.12) |
| Lowest quartile | 108,911 (76.36) | 12,497 (8.76) | 15,344 (19.76) | 5,408 (3.79) | 475 (1.00) |
| Unknown | 8,696 (80.39) | 751 (6.94) | 978 (9.04) | 355 (3.28) | 37 (0.89) |
| Father's gross income | |||||
| Highest quartile | 271,052 (71.51) | 37,426 (9.87) | 49,679 (13.11) | 19,451 (5.13) | 1,454 (1.28) |
| Second highest quartile | 184,028 (73.31) | 23,509 (9.36) | 31,398 (12.51) | 11,398 (4.54) | 702 (0.93) |
| Second lowest quartile | 77,164 (74.53) | 9,983 (9.64) | 11,838 (11.43) | 4,235 (4.09) | 308 (0.89) |
| Lowest quartile | 59,512 (76.01) | 7,227 (9.23) | 8,367 (10.69) | 2,926 (3.74) | 263 (1.01) |
| Unknown | 15,496 (73.52) | 1,682 (7.98) | 2,809 (13.33) | 940 (4.46) | 149 (1.84) |
| Mother's marital status | |||||
| Married | 201,354 (71.91) | 26,444 (9.44) | 36,330 (12.97) | 14,759 (5.27) | 1,137 (1.40) |
| Divorced | 13,196 (67.40) | 1,804 (9.21) | 3,168 (16.18) | 1,262 (6.45) | 148 (2.55) |
| Co-habiting | 380,426 (73.47) | 50,469 (9.75) | 63,006 (12.17) | 22,364 (4.32) | 1,522 (0.92) |
| Widow | 489 (69.46) | 44 (6.25) | 121 (17.19) | 46 (6.53) | 4 (2.29) |
| Unknown | 11,787 (79.09) | 1,066 (7.15) | 1,466 (9.84) | 519 (3.48) | 65 (1.09) |
| Co-morbidities | |||||
| Diabetes | 1,882 (42.53) | 418 (9.45) | 1,219 (27.55) | 864 (19.53) | 42 (2.45) |
| Gestational diabetes | 90 (27.69) | 41 (12.62) | 118 (36.31) | 74 (22.77) | 2 (1.05) |
| Placenta praevia | 638 (26.04) | 126 (5.14) | 874 (35.67) | 803 (32.78) | 9 (0.73) |
| Placental abruption | 1,854 (35.20) | 257 (4.88) | 2,523 (47.90) | 624 (11.85) | 9 (0.62) |
| Hypertensive disorders | 21,980 (50.75) | 4,951 (11.43) | 11,833 (27.44) | 4,361 (10.07) | 135 (0.88) |
| Infant birth weight (median [IQR]) | 3,400 (3,100, 3,725) | 3,546 (3,214, 3,864) | 3,450 (2,910, 3,900) | 3,200 (2,760, 3,570) | 3,370 (3,050, 3,694) |
| Infant length, in centimetres (median [IQR]) | 52 (50, 53) | 52 (51, 54) | 52 (50, 54) | 50 (49, 52) | 51 (50, 52) |
| Infant sex | |||||
| Female | 303,120 (74.74) | 34,514 (8.51) | 46,505 (11.47) | 20,021 (4.94) | 1,379 (1.10) |
| Male | 304,132 (71.15) | 45,313 (10.60) | 57,586 (13.47) | 18,929 (4.43) | 1,497 (1.13) |
| Gestation, in weeks (mean [SD]) | 39.97 (1.85) | 40.36 (1.58) | 39.44 (2.95) | 38.42 (2.48) | 38.84 (1.54) |
| Gestation | |||||
| Very preterm (<34 wk) | 4,702 (41.15) | 155 (1.36) | 4,847 (42.42) | 1,711 (14.97) | 12 (0.29) |
| Preterm (<37 wk) | 29,678 (55.75) | 2,324 (4.37) | 14,853 (27.90) | 6,219 (11.68) | 157 (0.83) |
| Term (37–41 wk) | 408,026 (75.28) | 48,147 (8.88) | 53,451 (9.86) | 29,852 (5.51) | 2,515 (0.46) |
| Post-term (41+ wk) | 159,881 (71.05) | 28,482 (12.66) | 33,962 (15.09) | 2,510 (1.12) | 198 (0.29) |
Data are n (percent) unless otherwise specified. All pregnancy- and infant-related characteristics are for the first (index) live birth.
*Maternally requested cesarean data available from 2002–2010 only (cohort n = 258,445).
a
Smoking data available 1997–2010 only (n = 405,498).
b
BMI data available 2003–2010 only (n = 230,066).
c
History of pregnancy loss before the first live birth.
IQR, interquartile range; SD, standard deviation.