Instrumental and operative delivery
Episiotomy
This is small cut made into the perineum to stop it tearing during delivery.
Augmentation
Essentially, this is where established labour is accelerated by artificial means. This is done by amniotomy where a hook is used to perform artificial rupture of the membrane (ARM). Another technique is use of oxytocin (trade name: syntocin) which can also accelerate the labour through a positive feedback mechanism.
Instrumental Delivery
In the second stage of labour, it is common for babies to get stuck on their way out. In such cases, instrumental delivery can help.
Forceps
I'm sure you've all seen a pair of forceps. These are ones specially designed for pulling out babies by the head. (I'll try and get a picture at some point.) They are used: in breech presentation; if mother or baby are distressed; if mother can no longer push; and during a prolonged second stage of labour.
Forceps can be used for rotation is the baby's head is not in the right position. They will rotate to the occipito-anterior (OA) position. Usually an episiotomy is needed and a great deal of bruising can be caused to the pelvic floor and tears inside the vagina are also common.
Vacuum
This is basically a suction cup (aka Ventouse) which is stuck on the babies head in order to yank it out. As long as the baby is in the OA position, a vacuum extraction is possible. It is used in: prolonged second stage or maternal exhaustion; fetal emergency during 2nd stage (e.g. drop in heart rate); and where maternal pushing would be risky (e.g. cardiac conditions).
It can leave a chignon on top of the baby's head. An episiotomy is required less often than with forceps and vacuum is associated with fewer injuries to the vagina internally.
Operative Delivery
The Caesarean section (C-section) is performed when it would be risky to perform vaginal delivery or where vaginal delivery has failed. This includes trying instrumental delivery if it is appropriate. The most commonly performed version of this operation is the lower uterine segment Caesarean section (LSCS) where the incision is made just above the bladder. It is safer and has fewer complications than its predecessor, the classical C-section where the incision is made down the midline - this is rarely done today.
Occasionally, obstetricians will perform the operation on women who do not have any vaginal delivery risk factors but simply do not want to go through with it. Generally, however, women are encouraged to perform a vaginal delivery wherever possible. About 25% of deliveries are done by C-section.