What a severe tear means years later
The part that is almost never disclosed beforehand.
In a network meta-analysis of 10 studies and 2,467 women, the average proportion reporting some degree of anal incontinence after a sphincter injury was:
| Depth of injury | Reporting anal incontinence |
|---|---|
| 3a, less than half the external sphincter torn | 22.4% |
| 3b, more than half the external sphincter torn | 24.9% |
| 3c, internal sphincter also torn | 26.8% |
| 4th degree | 28.6% |
Anal incontinence here includes leakage of gas as well as of stool, and gas is the commonest symptom. The analysis also compared the groups against each other statistically, finding higher odds with deeper tears: 1.79 times higher for a 3c tear and 2.37 times higher for a fourth-degree tear compared with a 3a tear. Those comparisons come from a statistical model that adjusts across studies, which is why they do not match what you would get by dividing the percentages in the table above.
Even without a recognised tear, damage happens. In a study scanning 202 women before and after birth, new sphincter defects were found in 35% of first-time mothers and 44% of women having a later baby, most with no clinically recognised tear at all. None of the 23 women delivered by cesarean had a new defect.