The purpose of the proposed study is to examine the relationship between cerclage suture material of Ethibond and Prolene and its effect on the vaginal microbiome in a prospective randomized control trial. Ethibond is another commonly used suture material for performing cervical cerclage that shares some characteristics with previously studied suture materials. It is braided like the Mersilene, but thinner like the monofilament Prolene. The investigators will study whether Ethibond causes the vaginal microbiome to be adversely affected like Mersilene or whether there is a healthy microbiome like Prolene. This study will allow the investigators to determine whether it is advisable to continue to use Ethibond for cervical cerclage in clinical practice, or whether obstetricians should avoid its use as now done with Mersilene.

Inclusion Criteria:

• Greater than18 years of age
• Singleton pregnancy
• History of preterm delivery between 17 0/7 weeks - 33 4/7 weeks with painless cervical

dilation or cervical insufficiency

Exclusion Criteria:

• younger than 18 years of age
• multiple gestation
• iatrogenic preterm delivery
• pregnancies with fetal anomalies