First-trimester and early-second-trimester transvaginal cervical length before 16 weeks among women with preterm and term birth: a systematic review and meta-analysis.

Objective: This study aimed to evaluate the differences in first-trimester and early-second-trimester transvaginal cervical length between patients with spontaneous preterm birth and those with term birth.

Data Sources: PubMed, MEDLINE, Embase, and the Cochrane Library were systematically searched through August 2023.

Study Eligibility Criteria: Studies had to include (1) transvaginal cervical length measurement before 16 weeks of gestation and (2) transvaginal cervical length measurement in a population of patients who delivered preterm and at term. Abstracts, studies with duplicated data, and those with cervical length measured by transabdominal ultrasound scan were excluded.

Methods: K.W.C. and J.L. searched for, screened, and reviewed the articles independently. The quality of the studies was assessed using the Newcastle-Ottawa scale. Mean differences were calculated using a random-effects model and pooled through a meta-analysis.

Results: A total of 5727 published articles were identified. Only 10 studies (which analyzed 22,151 pregnancies) met the inclusion criteria. All studies excluded iatrogenic preterm birth. Transvaginal cervical length was significantly shorter in women with spontaneous preterm birth than in those who delivered at term (mean difference, -0.97; 95% confidence interval, -1.65 to -0.29; P=.005; I=69%). When a linear technique was used to measure transvaginal cervical length, a significantly shorter transvaginal cervical length was associated with spontaneous preterm birth as opposed to term birth (mean difference, -1.09; 95% confidence interval, -1.96 to -0.21; P=.02; I=77%). A shorter transvaginal cervical length measured by other techniques was also associated with spontaneous preterm birth before 34 to 35 weeks (mean difference, -1.87; 95% confidence interval, -3.04 to -0.70; P=.002; I=0%). When studies where interventions were given for a "short" cervix or studies with a mean transvaginal cervical length ≥40 mm were excluded, a significantly shorter transvaginal cervical length was observed among those with spontaneous preterm birth (mean difference, -1.13; 95% confidence interval, -1.89 to -0.37; P=.004; mean difference, -0.86; 95% confidence interval, -1.67 to -0.04; P=.04; respectively). The optimal transvaginal cervical length cutoff was 38 to 39 mm, yielding pooled sensitivity of 0.80, specificity of 0.45, positive likelihood ratio of 1.16, negative likelihood ratio of 0.33, diagnostic odds ratio of 5.12, and an area under the curve of 0.75.

Conclusion: Women with spontaneous preterm birth had significantly shorter transvaginal cervical length before 16 weeks of gestation compared with those who delivered at term. The linear method and the 2-line method are acceptable techniques for measuring transvaginal cervical length.