SIMULTANEOUS MONITORING OF HEAD-TO-CERVIX FORCES, INTRAUTERINE PRESSURE AND CERVICAL DILATATION DURING LABOR

In many westernized countries, the caesarean section rate has now reac hed 15% or more, most commonly because of slow progress in labour. In order for labour to result in a vaginal delivery, the uterine cervix m ust dilate to allow the foetus to travel through the birth canal. This process is driven by uterine contractions, but the mechanisms by whic h the contractions result in cervical dilatation are still far from cl ear. The force exerted by the presenting part (foetal head) on the cer vical tissue during contractions (head-to-cervix force, HCF) has been shown to be the variable with the best correlation with cervical dilat ation. Unfortunately, the mechanism by which these two variables are r elated is still poorly understood in order to investigate the relation ship between head-to-cervix force, intrauterine pressure (IUP) and cer vical dilatation, we have developed a system for their simultaneous an d continuous monitoring during labour. The HCF is measured by using a novel intrauterine probe which is slipped alongside the foetal head so as to lie sandwiched between the latter and the cervix. The probe is fitted with six specially designed miniature force sensors, spaced 1.8 cm apart, which respond linearly and approximate the behaviour of loa d cells. They are interfaced with a PC by circuitry that allows auto-z eroing and drift compensation. The system enables simultaneous acquisi tion of intrauterine pressure and foetal heart rate (measured using a Sonicaid Meridian foetal monitor) via a serial link, together with con tinuous cervical dilatation measured by a caliper-like device applied to the cervix. Some preliminary data are presented which suggest that the system can be used to investigate the role played by head-to-cervi x force and intrauterine pressure in the cervix dilatation process. (C ) 1997 IPEM. Published by Elsevier Science Ltd.