Birth Injuries: Perineal Tears
Perineal tears (ie, tearing of the area between the vagina and anus) are birth injuries that happen during the second stage of labour as the baby is being delivered. However, they are not diagnosed until the third stage of labour, ie after the baby is born.
Perineal tears are graded from 1st degree to 4th degree according to their severity and are usually caused when the baby is delivered before the perineum has had a chance to slowly stretch widely enough to allow the baby to be born, or because the perineum is already scarred due to a previous injury causing it to be less stretchy than would be expected. This over-stretching of the perineum can result in birth injury.
The most common causes of perineal tears are:
- Inelastic perineal tissues/ insufficient stretching of the perineum/ excessive pressure on the perineum during the birth of the baby
- Baby is larger than normal: a baby over 9lbs in weight is usually considered large and can heighten the risk of birth injuries occuring.
- Narrow vaginal opening: if the vaginal opening is small but the baby is a normal size, this can mean a perineal tear may occur.
- Instrumental delivery of the baby: use of forceps or ventouse can cause damage to the perineal area.
- Shoulder Dystocia: the baby becomes trapped by its shoulders against the mother's pelvic bone after its head has been delivered; the resulting attempts to deliver the baby safely can cause injury to the perineum.
- Malpresentation of the baby: if the baby is lying in an awkward position such as occipito-posterior position (OP) ie, head down with its spine against its mother's (face presentation), then a tear to the perineum is more likely.
- Nulliparity: ie, the woman has never carried or given birth to a baby.
- Induction of labour
- Epidural analgesia
- Prolonged second stage of labour: ie, longer than 1 hour
- Midline episiotomy: ie, a surgical cut is made from the back of the vaginal opening straight toward the anus.
Although most perineal tears are very small, known as first degree tears, in some instances they can be more severe and result in second degree and even third degree injury to the mother.
