Early prognostic factors of outcomes in monochorionic twin pregnancy: systematic review and meta-analysis

Objective: Assess ability of first trimester pregnancy related factors (ultrasound measurements, maternal characteristics, biomarkers) to predict complications in monochorionic twin pregnancies Data sources: MEDLINE, EMBASE, ISI Web of Science, CINAHL, the Cochrane Central Registration of Controlled Trials and Research Registers, and Google Scholar, from inception to 12 May 2017. Grey literature and bibliographies of articles were checked. Study eligibility criteria: Studies that reported ultrasound measurements, maternal characteristics, or potential biomarkers, measured in the first trimester in monochorionic diamniotic twin pregnancies, where the potential prognostic ability between the variable and twin-twin transfusion syndrome, growth restriction, or intrauterine fetal death could be assessed. Study appraisal and synthesis methods: Quality assessment was evaluated using the STROBE checklist by 2 reviewers independently. For meta-analysis, odds ratios using a random effects model, or standardized mean difference were calculated. If a moderate association was found, the prognostic ability was evaluated by calculating the sensitivity and specificity. Risk of heterogeneity was reported as I2 and publication bias was visually assessed by funnel plots and quantitatively by Egger’s test. Results: Forty-eight studies were eligible for inclusion. Twenty meta-analyses could be performed. A moderate association was demonstrated in 3 meta-analyses, between: NT>95th centile in one/both fetuses and TTTS (OR 2.29 [95%CI 1.05, 4.96] I2=6.6%, 4 studies, 615 pregnancies); CRL discordance ≥10% and TTTS (OR 2.43 [95%CI 1.13, 5.21] I2=14.1%, 3 studies, 708 pregnancies); and maternal ethnicity and TTTS (OR 2.12 [95%CI 1.17, 3.83] I2=0.0%, 5 studies, 467 pregnancies), but none demonstrated a prognostic ability for any outcome under investigation. Conclusions: It is not currently possible to predict adverse outcomes in monochorionic twin pregnancies. We have revealed a lack of research investigating first trimester biomarkers in monochorionic twin pregnancies. Different assessment methods and definitions of each variable and outcome were an issue and this highlights the need for a large cohort study to evaluate these factors.