558: Short cervical length in low risk women: how many will become dilated before 24 weeks?

Abstract

It has been well established that short cervical length (CL) is associated with an increased risk of spontaneous preterm birth (SPTB). In women without a history of SPTB and a short CL found incidentally on ultrasound, previous studies have shown that cerclage is not associated with improved outcomes. Women with a dilated cervix, however, may benefit from cerclage. It is not well understood which women with a short CL will ultimately become dilated. We sought to determine what proportion of women with a short CL without a history of SPTB will ultimately be dilated at <24 weeks and thus be cerclage candidates. This was a retrospective cohort study of women with singleton pregnancies with short CL (≤25mm) between 16-22 weeks’ gestational age (GA) diagnosed at a single maternal-fetal medicine ultrasound unit between 2011 and May 2018. We included women without a history of SPTB. We routinely perform ultrasounds on women at 16 and 20 weeks GA and image the cervix in all women transabdominally. If the CL was suspected to be short, transvaginal imaging was performed. We routinely follow women with a short CL with serial CL’s, and speculum exams for those with a CL <10mm. We examined the progression of women based on the CL measurement and GA at diagnosis. The primary outcome was cervical dilation or spontaneous delivery <24 weeks. Chi square and logistic regression analysis was used. A total 163 women were included, of whom 27 (16.6%) were ultimately dilated and 4 (2.5%) had pregnancy loss by 24 weeks. The median GA at diagnosis of short CL was 19 5/7 (range 15-22) weeks. Women with a CL ≤15 were more likely to have dilation or pregnancy loss prior to 24 weeks than women whose CL was 16-25mm (42.5% vs. 11.9%, <0.001). GA at diagnosis was not associated with risk of progression. After controlling for differences in baseline characteristics including GA at short CL diagnosis, in vitro fertilization, and history of cervical cone biopsy or loop electrosurgical excision procedure, CL ≤15mm was independently associated with almost a 4-fold increase in odds of dilation or loss (aOR 3.72, 95% CI 1.52-9.09). In women with a short CL without a history of SPTB, the risk of dilation or pregnancy loss <24 weeks is significant, approaching 50% for women with a CL ≤15mm. This supports the practice of serial CL measurements in women found to have a short cervix, especially with a CL ≤15mm, in order to identify those who may become dilated and potentially benefit from an exam-indicated cerclage.