2.1.1 Literature search
The Cochrane Library, PubMed, EMbase, WanFang Data, CNKI, VIP Data and
CBM Data were electronically searched to collect randomized controlled
trials (RCTs) and non-randomized controlled trials (non-RCTs, including
cohort studies) comparing cervical pessary and transvaginal cervical
cerclage in preventing spontaneous preterm birth. According to the
PRISMA Guidelines and the Cochrane Handbook for Systematic Reviews of
Interventions[6-7], the literature search was
conducted using MeSH terms combined with entry terms (e.g., pessaries,
pessary, cervical cerclage, cerclage, cervical, premature birth, preterm
birth, etc.). Taking PubMed for example, the detailed search strategy is
provided in Box 1-1. All electronic databases were searched from their
inception to August 31, 2020.