The force required to dilate the uterine cervix to a diameter of 8 mm has been measured in 200 non-pregnant and 40 early pregnant patients. In general, the resistance offered by the cervix was lower in parous than in nulliparous subjects and in pregnant compared with non-pregnant subjects. The phase of the menstrual cycle did not appear to influence cervical resistance but the highest recordings were seen in postmenopausal subjects. Particularly low resistance was encountered in women receiving Depo-Provera for contraceptive purposes.
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Anthony et al. (1982) studied this question.
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