Fig. 98.—Measuring the diagonal conjugate with the finger. (Eden.)
A circumference of 90 cm. corresponds to an inlet of 11 cm. in its anteroposterior diameter, and every variation of 5 cm. in this circumference makes a difference of 1 cm. (either larger or smaller) in the anteroposterior diameter.
Thus, 95 cm. in circumference=12 cm. in the diameter; and 85 cm. in circumference=10 cm.
Complications increase in proportion to the degree of contraction in the pelvis.
The most frequent difficulties superinduced by the small pelvis are prolapse of the cord, malpresentation and malpositions of the head, prolonged labor, and a large increase in the number of assisted deliveries.
All the possibilities and probabilities in a given case will be carefully worked out before labor by the conscientious obstetrician, and Cæsarean section, induction of premature labor, pubiotomy, forceps, or version and extraction, will be done with a sure foreknowledge.
Prolapse of the cord complicates labor once in about two hundred cases. It is most likely to occur when the presenting part does not enter or does not entirely fill the opening, as in transverse or shoulder presentations, or vertex presentations with small inlets.
The mother is not endangered by this mishap, but the babe is lost in from 35 to 60 per cent of the cases.
The diagnosis is easily made when a loop of cord protrudes from cervix or vulva, and the pulsation will differentiate it from everything else.
If the cord does not pulsate, the family should be informed that the child is dead and the case may be allowed to terminate normally.