Determination of the elastic properties of the cervix.

The elastance of the uterine cervix of nonpregnant women was measured by placing a 3- or 4-cm compliant balloon in the cervical canal and determining its pressure-volume characteristic while filling with up to 5 mL of sterile water at a rate of 12 mL/minute. The mean elastance for 247 patients who had previously suffered either one or more spontaneous midterm pregnancy losses, preterm birth, or three or more early spontaneous abortions was significantly lower than that of 42 controls who did not meet these criteria. Elastances were significantly lower in groups having a clinically observed patulous cervix or laceration, or a clinically diagnosed incompetent cervix, than in the normal cervix group. No significant difference was found between the follicular and luteal phases for 64 regularly cycling women. Values were significantly reduced in women showing a widened cervix on a hysterosalpingogram when compared with those with a normal-appearing cervix. When larger Hegar dilators were passed without resistance, the elastance was generally lower, although there was not always good correlation between the largest dilator passed and elastance.