The development of an instrument for monitoring dilatation of the cervix during labour.

The measurement of cervical dilatation during labour is of fundamental importance to the obstetrician as it indicates the progress of labour. This paper reviews instruments that have been used to measure cervical dilatation in the past and describes the development of an instrument, originally intended to measure both effacement of the cervix and cervical dilatation, but which, because of technical problems, resulted in an instrument measuring cervical dilatation only. The instrument is non-traumatic, accurate, and easy to apply. As well as the clinical application, the instrument has been found useful in studying mechanism of dilatation. Preliminary results have shown that the cervix opens in an oscillatory manner dictated by the strength and period of uterine contractions. It can even close slightly following a series of weak contractions. Further clinical trials are planned.