Fig. 6.—Diagram showing method of measuring distances between iliac crests and spines and the trochanters.
The inlet has four measurements of obstetrical importance: the antero-posterior, or true conjugate, which is the distance from the top of the symphysis pubis to the prominence of the sacrum, and is normally 11 centimetres; the transverse diameter, which is at right angles to the true conjugate and is the greatest width of the inlet, measuring from a point on one side of the brim to the corresponding point on the other, is normally 13.5 centimetres, and the two diagonal measurements, known respectively as the right and left oblique diameters, which are normally 12.75 centimetres.
Although it is very important to the expectant mother that all of these dimensions be of normal length, the length of the true conjugate, or conjugata vera, is of the gravest importance of all because it is the shortest diameter through which the child’s head must pass. If it is shorter than normal, the channel may be too constricted for the full-term baby’s head to pass through comfortably, thus making a spontaneous delivery extremely difficult, or even impossible.
Fig. 7.—Diagram showing method of measuring Baudelocque’s diameter.
The length of the all important, true conjugate is estimated by introducing the first two fingers of one hand into the vagina until the tip of the second finger touches the promontory of the sacrum. (Fig. [8].) The point at which the inner margin of the symphysis then rests upon the forefinger is measured, thus giving the length of the diagonal conjugate. This normally measures 12.5 centimetres or more, and is estimated as being 1.5 centimetres longer than the true conjugate.
The most important measurement of the outlet is the intertuberous diameter, the distance between the tuberosities of the ischii. This is the shortest diameter through which the child must pass in the inferior strait, and normally measures something more than 8 centimetres, usually about 11 centimetres. (Fig. [9].)
It is possible, by studying such measurements as these, made upon an expectant mother, and comparing them with dimensions which have been accepted as normal, to form a reasonably accurate estimate of the size and shape of her pelvis.
