Abstract: A balloon catheter (2) of apparatus (1) for monitoring ripening of a cervix (3) in a female subject prior to the onset of labour in a pregnancy comprises a cervix engaging balloon 10 located distally on a catheter (7). The balloon (10) is located in the cervix (3) and inflated with air by a syringe (85) to a pressure of approximately 80 mmHg. As the cervix (3) commences to ripen an opening (11) extending through the cervix (3) increases in volume thus resulting in a fall in pressure in the cervix engaging balloon (10). A microprocessor (86) in a housing 82 on the catheter (7) monitors the pressure in the balloon at predetermined time intervals and determines the volume of the opening (11) extending through the cervix (3) from a look-up table.