Table 2 Prevalence (%) of OASIS in relation to birth position
| Â | Â | Total | Sitting | Lithotomy | Lateral | Knee | Birth seat | Supine | Squatting | Standing | All fours | Unknown |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Nulliparous women | N of OASIS | 2 548 | 931 | 850 | 250 | 126 | 279 | 58 | 15 | 9 | 13 | 17 |
OASIS (%) | 5.7 | 5.4 | 7.1 | 4.3 | 4.7 | 5.7 | 4.8 | 4.4 | 3.7 | 5.5 | 6.0 | |
 3rd degree (%) | 5.2 | 4.9 | 6.5 | 4.0 | 4.3 | 5.1 | 4.4 | 3.8 | 3.7 | 5.5 | 5.5 | |
 4th degree (%) | 0.5 | 0.5 | 0.6 | 0.3 | 0.4 | 0.6 | 0.4 | 0.6 | 0.0 | 0.0 | 0.5 | |
Parous women | N of OASIS | 859 | 323 | 194 | 124 | 70 | 82 | 37 | 10 | 5 | 6 | 8 |
OASIS (%) | 1.3 | 1.2 | 2.6 | 1.0 | 0.9 | 1.6 | 1.0 | 2.1 | 0.6 | 1.4 | 1.8 | |
 3rd degree (%) | 1.1 | 1.1 | 2.0 | 0.9 | 0.8 | 1.4 | 0.9 | 1.7 | 0.6 | 1.2 | 1.7 | |
 4th degree (%) | 0.2 | 0.1 | 0.6 | 0.1 | 0.1 | 0.2 | 0.1 | 0.4 | 0.0 | 0.2 | 0.1 | |
Women undergoing VBAC | N of OASIS | 301 | 100 | 106 | 32 | 16 | 27 | 13 | 3 | 1 | 1 | 2 |
OASIS (%) | 10.6 | 9.5 | 12.3 | 8.3 | 10.7 | 12.0 | 18.2 | 14.3 | 5.6 | 6.3 | 11.8 | |
 3rd degree (%) | 10.2 | 9.5 | 10.9 | 7.4 | 10.7 | 11.6 | 18.2 | 14.3 | 5.6 | 1.2 | 11.8 | |
 4th degree (%) | 0.6 | 0.0 | 1.4 | 1.0 | 0.0 | 0.4 | 0.0 | 0.0 | 0.0 | 0.2 | 0.0 |