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. [Illustration: 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. [Illustration: FIG. 8.—Diagram showing method of estimating the true conjugate by measuring the length of the diagonal conjugate. ] A delivery may be, and frequently is, accomplished through a pelvis which is not entirely normal in size or shape. But the obstetrician of to-day is closely observant of the patient whose pelvic measurements depart from the normal by more than the accepted margin of safety, and he plans for labor in accordance with the indications in each case. Disproportion between the measurements of the mother’s pelvis and the size of the child’s head must be considered in this connection. A small pelvis may permit of the spontaneous delivery of a small child, but be too narrow for the passage of a full-sized baby, while a woman with a normal pelvis may have an extremely difficult labor because of an unusually large child. The size and shape of the pelvis is found to vary among different races and in different individuals. And the size and contour of the inlet may be so altered by rickets, lack of proper exercise during early life, or by growths upon the pelvic bones, as to seriously interfere with normal labor. [Illustration: FIG. 9.—Diagram showing method of measuring the inter-tuberous diameter. ]