Hello - quick run down of the why's and how's, but off top of my head so might be bit confusing, sorry!
Vaginal examinations are 2 fingers. There would be no point putting anymore in, as the physiology of the pelvis is such you couldn't do anything usefull with your 3rd and 4th finger. They take anywhere from 10 seconds to a couple of mins.
For induction process/?onset of labour/?progress in labour assessment/?ruptured membranes, the mw will use the 2 finger tips to feel the cervix, how many cms it's open, how thick and stretchy it is, and something called effacement which is the drawing up of the main body of the cervix into the lower segment of the uterus.
Then the assessment will look at the baby in relation to the cervix, how well the head is applied to the cervix, and if there are lines on the baby's head that help us understand the lie of the baby, and also for swelling[caput] and moulding of the skull. Also feel for membranes inact or rupures, if bulging or tight. The examiner will give an overall opinion of the station of the head in the pelvis - thats is, how low it is in relation to your spines, which we have a mental image of location-wise.
These internals would be suggested to help you decide on what and when to have pain relief, to assess if you are OK to start pushing if the urge is building and building and there is no head visable, if the baby is looking stressed [a stresssed baby at 3cm can be an entirely different management issue to a stressed baby at fully dilated for example], if you request as you wish to know the labour is working and how it's going [like when people come in to delivery suite wondering if they are in labour] - and also as a 'routine', done about 4 hourly to pinpoint lack of progress in labour and chart the 'vibe' for your labour so staff can identify changes.
If a Dr is examining for a forceps delivery, and applting forceps - they will still use their 2 fingers, but may insert deeper as the cervix is gone, so they can reach round the head more - and they need to be 100% certain of the baby's position before putting on any instrument. If the lines on the head are difficult to read due to molding or the head is tilted or something, they can check for the ridges over the eyes, ears and other land marks to satisfy themselves as to position. This is more specialised management and not everyone wishes to know the ins and outs of it all!
What snow describes [I imagine] is the dr using their hands as the forceps [put your hands around the back of your head cupping your skull, fingers together and you get the idea] to try and do some advanced and very specific steering of the head through the bony pelvis. So more of a delivery mode rather than an assessment tool iuswim.
They are done [as is everything] with your consent. The MW may say 'I'm going to examine you' which does not imply choice, but if you say no then that is that in fact.
In terms of discomfort and pain - well, that varies so so much. Because of when they are done, where the cervix is, how it is tilted, if you are contracting, if you are not, what pain relief you have on board and so on. Add to that the impact of our mental state, degree to which they bother us, if we gel with the person examining, how safe we feel - and it's very unpredictable.
Entonox can help some through examinations, as its hard to tense your muscles when your high! others would hate that as they need to feel in control and 'there'. They generally don't hurt at all with epidurals.
My general advice - try try try not to squeeze your bum muscles. You'll feel more of the exam if you do [think of sex and gripping...well you get the idea]. If you are tense about them, it's often a nonsense to 'try to relax' - if they freak you they freak you - but try squeeze your toes or push your tounge into roof of your mouth to relieve the tension.
EachPeach - women do labour without examinations, through their choice and the lack of actual clinical need. In your situation it's probably worth discussing this with the consultant prior to the Vbac. The big big thing with Vbac is progress, they'll want to see that the body is responding to the contractions you are having. If the cervix is not responding - this can be the body's way of saying 'this baby doesn't fit' or 'not today thank you'. Missing that message when there is a uterine scar to consider could lead to a weakening of the uterus [it thins as the muscles struggle to push the baby through] and thats the big worry with any Vbac.
Maybe a plan of when the internals might take place would help you? A predictable pattern so you are ready for them? One for a senior body who knows your story. Am sorry they are a problem though.
Do apologise for such a long posting - but I find that alot of the stuff on the pregnancy type websites is way to simplistic. Perhaps I have gone to far other way!!