Management of Cervical Weakness Based on the Measurement of Cervical Resistance Index

Abstract

Although treating cervical weakness after dilation has rescued many pregnancies, there is a trend toward performing cerclage before the cervix has begun dilating, and this requires a diagnostic test to confirm cervical weakness. This observational study measured the cervical resistance index (CRI)-the force required to dilate the cervix to 8 mm-as an aid in choosing which women with a history of spontaneous mid-trimester miscarriage should have cervical cerclage in subsequent pregnancies. The study group included 175 nonpregnant women with a history of one or more spontaneous mid-trimester losses at 12 to 28 weeks' gestation, and the control group comprised 123 nonpregnant women having CRI measurements during routine gynecological surgery. Women whose CRI indicated an incompetent cervix were advised to have cervical cerclage in future pregnancies. A CRI below 5 1b, or 22 Newtons (N), was taken as an indicator of cervical weakness. The study and control women had median CRI values of 17 and 38 N, respectively. Thirty study women were considered to have a competent cervix by CRI while the obstetrical history suggested otherwise. At the same time, 32 study women had a CRI suggesting an incompetent cervix despite a history indicative of cervical competence. Of 486 previous pregnancies in the 175 study women, 27% had a successful outcome. Subsequently, 94 of these women have had 148 pregnancies, 76% of which had a successful outcome. This study showed that nonpregnant women with a history of spontaneous mid-trimester miscarriage have significantly lower cervical resistance indices than parous women without mid-trimester loss, although the CRI was not in accord with the past history in more than one-third of the present patients. Measuring the CRI may help to detect cervical weakness and thereby to decide when prophylactic cervical cerclage is appropriate in subsequent pregnancies.