• Marinela Grabovac, Anne Mary Lewis-Mikhael, and Sarah D McDonald.
• Department of Obstetrics & Gynecology, McMaster University, Hamilton, ON. Electronic address: marinela.grabovac@medportal.ca.
• J Obstet Gynaecol Can. 2019 Jan 1; 41 (1): 76-88.e7.

ObjectivesThe most effective preterm birth (PTB) intervention is unknown for women who are at risk of PTB due to a history of conization. The objective of this systematic review was to determine whether PTB interventions, progesterone, cerclage, and pessary decrease the risk of PTB compared to no treatment in singleton-and separately in twin-pregnancies of women with history of conization.MethodsWe searched Cochrane Central, MEDLINE, EMBASE, CINAHL, and ClinicalTrials.gov from January 1994 until May 2017. In duplicate, we reviewed titles, abstracts, full texts, extracted data, and assessed quality. We included RCTs and observational studies. Our primary outcomes were PTB <34 weeks, PTB <37 weeks, and neonatal mortality. We performed random effects meta-analyses and generated ORs with 95% CIs.ResultsWe screened 762 nonduplicate titles and abstracts and assessed 91 full texts. After contacting authors, we included nine studies. Women in the cerclage group were more likely to have a short cervix or another risk factor for PTB, raising the possibility of confounding by indication. In women with a history of conization and a singleton who received a cerclage compared to those who did not, the ORs of PTB <34 weeks was 3.99 (95% CI 0.67-23.62, three studies, I2 = 65%); of PTB <37 weeks was 2.10 (95% CI 0.87-5.05, four studies, I2 = 0%); and of neonatal mortality was 8.33 (95% CI 0.22-320.38, two studies, I2 = N/A). We did not find any studies comparing either progesterone or pessary to no treatment. Data for twins were very scarce.ConclusionIn women with a previous conization and a current singleton gestation, the existing evidence, which is likely limited due to confounding by indication, does not support cerclage or other interventions used to try to decrease PTB.Copyright © 2019 Society of Obstetricians and Gynaecologists of Canada. Published by Elsevier Inc. All rights reserved.

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