The correct choice is (b) Intrauterine pressure measurement
Easy explanation: The following techniques are commonly used in uterine contraction in most of the cardiotocographic monitoring: I) Indirect method: Tocodynamometry (using tocotonometer to sense changes in uterine tension transmitted to abdominal skin surface) II) Direct method: Intrauterine pressure measurement (using a fluid-filled intracervical catheter with strain gauge transducer).