The natural history of a positive response to transfundal pressure in women at risk for cervical incompetence

OBJECTIVE: Our purpose was to observe the evolution of the endocervical canal length in women at risk for cervical incompetence after a positive response to transfundal pressure. STUDY DESIGN: Ten women at risk for cervical incompetence had a midtrimester cervical evaluation with transvaginal ultrasonography and transfundal pressure. With a transvaginal probe, the endocervical canal length was first measured. Transfundal pressure was then applied and the endocervical canal length was remeasured. All patients had a positive response to transfundal pressure as defined by a decrease in endocervical canal length after application of transfundal pressure. At the initial evaluation the digital examination of the cervix had revealed a closed and long cervix in all 10 cases. In 9 of the 10 patients repeat examinations were performed until the endocervical canal length progressively shortened to <10 mm or the digital examination revealed a dilated cervix. The endocervical canal lengths after application of transfundal pressure from the first and last examination were compared. One patient was lost to follow-up, but the obstetric outcome was available. RESULTS: The median time interval between the first and final examination was 7 (2 to 20) days in 9 of the patients. The median (range) gestational age at the first and final examination was 19.0 (15 to 22) weeks (n = 10) and 20.5 (18 to 24) weeks (n = 9), respectively. There was significant shortening of the endocervical canal length from the first to the last examination; 12.2 (4 to 20) mm (n = 10) versus 0.0 (0 to 9.5) mm (n = 9), p = 0.008. Six patients had membranes at the external cervical os before application of transfundal pressure at the last examination. The one patient lost to ultrasonographic follow-up had a pregnancy loss at 23 weeks of gestation, 6 weeks after a positive response to transfundal pressure. CONCLUSION: In patients at risk for cervical incompetence, shortening of the endocervical canal length in response to transfundal pressure requires treatment with a cervical cerclage because it is associated with progressive cervical changes over 1 to 3 weeks.