The most usual circumstances under which the forceps is applied, are where the head is already deep in the pelvis and approaching the os externum; in such cases it is generally required not so much for the purpose of overcoming an unusual degree of resistance, as for assisting the natural powers, which are becoming exhausted: the head is near the os externum, and therefore easily reached; and from there being little or no impaction present, the blades are applied without difficulty.
The application of the forceps when the head is at the upper part of the pelvis, and where the greater portion of it has not yet passed the brim, is rarely practised in this country, because as the necessity for performing the operation at this stage arises in most instances from contraction of the brim, the perforator has usually been preferred, wherever the expelling powers have proved incapable of overcoming the resistance to the passage of the head. The circumstance also of this condition requiring the long forceps has been another source of objection, from the much greater power which this instrument is capable of exerting, and from its being therefore more liable than the short forceps to prove mischievous in the hands of the inexperienced.
Cases however do occur where there is but a very slight want of proportion between the head and pelvis, where the obstacle is easily overcome, and where, but for the application of the forceps, the labour would either have been protracted to a dangerous degree, or have required the use of the perforator.[84] "On the whole," says Dr. Burns, "I would give it as my opinion that a well instructed practitioner, who has already had some experience in the use of the short forceps, is warranted to make a cautious, steady, but gentle attempt to apply and act with the long forceps in a case where he is not quite decided that the perforator is indispensable, and where the head is higher than admits the application of the short forceps." (_Principles of Midwifery_, 9th ed. p. 493.)
In applying the forceps, whether short or long, there are two conditions which, _cæteris paribus_, are requisite in every case; first, that the os uteri shall be fully dilated; secondly, that the pains are within the bounds of what are commonly known as moderate pains. In the first case it will be very difficult and frequently quite impossible to pass the blades between the head and os uteri when only partly dilated; it will be difficult to avoid injuring its edge more or less, and if we do succeed in applying and locking the forceps, on making an extractive effort we shall find that the uterus descends with the head as we draw it down.