Table 1.
Variables analyzed, and rates of obstetric anal sphincter injury (OASI) in each variable category: singleton, live, term, vaginal 1st, 2nd and 3rd births, Sweden 1999–2011
| Variables | 1st births | 2nd births | 3rd births | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Prevalence of variables | Rates of OASI | Prevalence of variables | Rates of OASI | Prevalence of variables | Rates of OASI | ||||
| n (436670) | % | (%) | n (379787) | % | (%) | n (140102) | % | (%) | |
| Maternal age (years) | |||||||||
| < 25 | 111,828 | 25.6 | 4.1 | 38,677 | 10.2 | 1.0 | 5232 | 3.7 | 0.4 |
| 25–29 | 163,471 | 37.4 | 6.9 | 117,498 | 30.9 | 2.0 | 29,102 | 20.8 | 0.6 |
| 30–34 | 121,833 | 27.9 | 8.0 | 153,263 | 40.4 | 2.7 | 57,036 | 40.7 | 0.8 |
| ≥ 35 | 39,538 | 9.1 | 7.8 | 70,349 | 18.5 | 3.0 | 48,732 | 34.8 | 1.1 |
| Year of birth | |||||||||
| 1999–2004 | 185,654 | 42.5 | 7.0 | 161,407 | 42.5 | 2.5 | 62,560 | 44.7 | 1.0 |
| 2005–2011 | 251,016 | 57.5 | 6.3 | 218,380 | 57.5 | 2.2 | 77,542 | 55.3 | 0.8 |
| Education | |||||||||
| Elementary: ≤ 9 years | 43,820 | 10.0 | 4.2 | 35,170 | 9.3 | 1.6 | 19,189 | 13.7 | 0.7 |
| High school | 175,631 | 40.2 | 6.0 | 163,317 | 43.0 | 2.2 | 63,376 | 45.2 | 0.8 |
| College or university | 205,730 | 47.1 | 7.6 | 174,711 | 46.0 | 2.6 | 54,505 | 38.9 | 1.0 |
| Missing | 11,489 | 2.6 | 6589 | 1.7 | 3032 | 2.2 | |||
| Country/region of birth | |||||||||
| Sweden | 357,730 | 81.9 | 6.6 | 309,967 | 81.6 | 2.4 | 107,752 | 76.9 | 0.9 |
| Asia | 33,177 | 7.6 | 7.4 | 28,907 | 7.6 | 2.3 | 14,270 | 10.2 | 0.9 |
| Africa | 7163 | 1.6 | 9.0 | 7171 | 1.9 | 3.1 | 4807 | 3.4 | 1.2 |
| Other | 38,600 | 8.8 | 5.6 | 33,742 | 8.9 | 1.9 | 13,273 | 9.5 | 0.7 |
| Smoking in early pregnancy | |||||||||
| No | 381,092 | 87.3 | 6.8 | 335,534 | 88.3 | 2.4 | 119,673 | 85.4 | 0.9 |
| Yes | 33,734 | 7.7 | 3.9 | 25,689 | 6.8 | 1.4 | 13,573 | 9.7 | 0.6 |
| Missing | 21,844 | 5.0 | 18,564 | 4.9 | 6856 | 4.9 | |||
| BMI | |||||||||
| Low: <18.5 | 12,152 | 2.8 | 6.4 | 7824 | 2.1 | 2.1 | 2015 | 1.4 | 0.4 |
| Normal weight: 18.5–24.9 | 260,128 | 59.6 | 6.5 | 210,403 | 55.4 | 2.2 | 71,198 | 50.8 | 0.9 |
| Overweight: 25–29.9 | 83,185 | 19.0 | 6.8 | 84,411 | 22.2 | 2.5 | 34,887 | 24.9 | 0.9 |
| Obese: ≥ 30 | 31,333 | 7.2 | 6.2 | 35,013 | 9.2 | 2.6 | 15,749 | 11.2 | 0.8 |
| Missing | 49,872 | 11.4 | 42,136 | 11.1 | 16,253 | 11.6 | |||
| Infant birthweight (g) | |||||||||
| < 3000 | 52,966 | 12.1 | 2.7 | 26,046 | 6.9 | 0.9 | 9447 | 6.7 | 0.3 |
| 3000–3499 | 163,269 | 37.4 | 4.5 | 111,404 | 29.3 | 1.3 | 38,161 | 27.2 | 0.4 |
| 3500–3999 | 157,192 | 36.0 | 7.5 | 150,736 | 39.7 | 2.3 | 54,542 | 38.9 | 0.8 |
| 4000–4499 | 53,342 | 12.2 | 11.9 | 73,289 | 19.3 | 3.7 | 29,503 | 21.1 | 1.3 |
| ≥ 4500 | 8818 | 2.0 | 18.0 | 17,538 | 4.6 | 5.9 | 8168 | 5.8 | 2.6 |
| Missing | 1083 | 0.2 | 774 | 0.2 | 281 | 0.2 | |||
| Presentation | |||||||||
| Occiput anterior | 407,784 | 93.4 | 6.4 | 354,776 | 93.4 | 2.3 | 130,554 | 93.2 | 0.8 |
| Occiput posterior | 14,355 | 3.3 | 10.8 | 12,375 | 3.3 | 4.0 | 4645 | 3.3 | 1.5 |
| Breech | 1405 | 0.3 | 4.3 | 978 | 0.3 | 1.6 | 327 | 0.2 | 0.6 |
| Other | 13,126 | 3.0 | 6.9 | 11,658 | 3.1 | 2.6 | 4576 | 3.3 | 1.3 |
| Diabetes | |||||||||
| No | 435,364 | 99.7 | 6.6 | 378,146 | 99.6 | 2.3 | 139,359 | 99.5 | 0.9 |
| Yes | 1306 | 0.3 | 8.7 | 1641 | 0.4 | 5.0 | 743 | 0.5 | 1.5 |
| Gestational diabetes | |||||||||
| No | 433,683 | 99.3 | 6.6 | 376,826 | 99.2 | 2.3 | 138,580 | 98.9 | 0.9 |
| Yes | 2987 | 0.7 | 8.1 | 2961 | 0.8 | 3.3 | 1522 | 1.1 | 1.0 |
| Pregestational hypertension | |||||||||
| No | 434,666 | 99.5 | 6.6 | 377,874 | 99.5 | 2.3 | 139,239 | 99.4 | 0.9 |
| Yes | 2004 | 0.5 | 7.0 | 1913 | 0.5 | 2.1 | 863 | 0.6 | 0.9 |
| Preeclampsia | |||||||||
| No | 423,794 | 97.1 | 6.6 | 375,404 | 98.8 | 2.3 | 138,380 | 98.8 | 0.9 |
| Yes | 12,876 | 2.9 | 6.2 | 4383 | 1.2 | 2.3 | 1722 | 1.2 | 0.9 |
| Epidural analgesia | |||||||||
| No | 234,246 | 53.6 | 6.1 | 308,153 | 81.1 | 2.0 | 121,796 | 86.9 | 0.8 |
| Yes | 202,424 | 46.4 | 7.1 | 71,634 | 18.9 | 3.6 | 18,306 | 13.1 | 1.1 |
| Episiotomy | |||||||||
| No | 376,486 | 86.2 | 6.2 | 363,439 | 95.7 | 2.2 | 137,265 | 98.0 | 0.8 |
| Yes | 60,184 | 13.8 | 8.6 | 16,348 | 4.3 | 5.6 | 2837 | 2.0 | 2.5 |
| Vacum extraction or forceps | |||||||||
| No | 362,249 | 83.0 | 5.0 | 364,529 | 96.0 | 2.0 | 136,860 | 97.7 | 0.8 |
| Yes | 74,421 | 17.0 | 14.4 | 15,258 | 4.0 | 10.6 | 3242 | 2.3 | 4.3 |
| Second births only | |||||||||
| History of OASI in 1st pregnancy | |||||||||
| No | 320,913 | 84.5 | 2.0 | ||||||
| Yes | 16,531 | 4.4 | 7.3 | ||||||
| Missing | 42,343 | 11.1 | |||||||
| History of cesarean section 1st pregnancy | |||||||||
| No | 312,869 | 82.4 | 1.6 | ||||||
| Yes | 24,575 | 6.5 | 10.3 | ||||||
| Missing | 42,343 | 11.1 | |||||||
| Third births only | |||||||||
| History of OASI in 2nd pregnancy | |||||||||
| No | 121,980 | 87.1 | 0.7 | ||||||
| Yes | 1688 | 1.2 | 7.6 | ||||||
| Missing | 16,434 | 11.7 | |||||||
| History of cesarean section 2nd pregnancy | |||||||||
| No | 121,305 | 86.6 | 0.7 | ||||||
| Yes | 2363 | 1.7 | 2.4 | ||||||
| Missing | 16,434 | 11.7 | |||||||