Measurement Of the Diagonal Conjugate

Measurement Of the Diagonal Conjugate

The True conjugate can only be measured directly after labour by a special instrument. An estimate of the true conjugate is, however, made by passing two fingers of the right hand backwards and upwards into the vagina till the end of its middle finger touches the promontory of the sacrum.

The hand is then carried upwards and forwards until its indexfinger touches the apex of the pubic arch. The index finger of the left hand is then placed at the point of contact, the fingers are withdrawn from the vagina, and the distance between the tip of the middle finger of the right hand and where the index finger of the right hand has touched the pubic arch is measured with a tape measure. Normally the measurement  shouldbe 4.75 inches.
Thus to ascertain the measurement of the true conjugate, 0.75 inch must be deducted from that of the diagonal conjugate.