True about vaccum extraction of fetus :
(A)Can be used in non dilated cervix
(B)Can be used in incompletely dilated cervix
(C)Used in Face presentation
(D)Applied 3cm post, to Anterior fontanel
(E)Applied 3cm ant. to posterior fontanel
The centre of the cup should be over the sagittal suture and about 3 cm in front of the posterior fontanel toward the face.

Anterior placement on the fetal cranium-near the anterior fontanel rather than over the occiput-will result in cervical spine extension unless the fetus is small'-
William's Obstetrics 23rd/523 Ventouse Extraction: Indications As an alternative to forceps operation
As an alternative to rotational forceps as in occipital transverse or posterior position  Delay in the descent of the head in case of the second baby of twins.
Delay in the late first stage of labour (uterine inertia). Conditions To Be Fulfilled
There should not be slightest bony resistance below the head.
The head of a singleton baby should be engaged.
Cervix should be at least 6 cm dilated (preferably only cervical rim may be left behind).

Contraindications:

Any presentation other than vertex (face, brow, breech)
Preterm fetus (<34 weeks). Chance of scalp avulsion or sub-aponeurotic haemorrhage.
Suspected fetal coagulation disorder.
Suspected fetal macrosomia
AB
BE
CA
DB