title: Evolution of Stage 1 Twin-to-Twin Transfusion Syndrome (TTTS): Systematic Review and Meta-Analysis.
abstract: The natural history of stage 1 Twin-to-twin transfusion syndrome (TTTS) remains unclear and its optimal management is yet to be established. The main aims of this meta-analysis were to quantify the incidence of progression in stage 1 TTTS and to ascertain survival in these pregnancies.
  
  
  
  MEDLINE, EMBASE, and The Cochrane Library were searched. Reference lists within each article were hand-searched for additional reports. The outcomes included incidence of progression and survival in stage 1 TTTS. Randomized controlled trials, cohort and case-control studies were included. Case reports, studies including three or fewer cases of stage 1 TTTS, and editorials were excluded. Proportion meta-analysis was used for analysis (Registration number: CRD42016036190).
  
  
  
  The search yielded 3,085 citations; 18 studies were included in the review (172 pregnancies to assess progression and 433 pregnancies to assess the survival). The pooled incidence of progression in stage 1 TTTS was 27% [95% CI 16-39%]. The pooled overall survival, double survival and at least one survival in the pregnancies managed expectantly were 79% [95% CI 62-92%], 70% [95% CI 54-84%] and 87% [95% CI 69-98%], respectively. In those undergoing amnioreduction, the corresponding figures were 77% [95% CI 68-85%], 67% [95% CI 57-76%] and 86% [95% CI 76-94%], respectively. The survival rates were 68% [95% CI 54-81%], 54% [95% CI 36-72%], and 81% [95% CI 69-90%], when laser surgery was performed.
  
  
  
  The optimal initial management of stage 1 TTTS remains in equipoise. The ongoing randomized trial comparing immediate laser surgery versus conservative management should provide a definitive answer.
authors.affiliation: Fetal Medicine Unit,St. George's University of London,London,UK.
authors.forename: Asma
authors.initials: A
authors.lastname: Khalil
authors.affiliation: Fetal Medicine Unit,St. George's University of London,London,UK.
authors.forename: Emily
authors.initials: E
authors.lastname: Cooper
authors.affiliation: Fetal Medicine Unit,St. George's University of London,London,UK.
authors.forename: Rosemary
authors.initials: R
authors.lastname: Townsend
authors.affiliation: Fetal Medicine Unit,St. George's University of London,London,UK.
authors.forename: Basky
authors.initials: B
authors.lastname: Thilaganathan
mesh_terms: D000328:Adult; D001163:Arteriovenous Anastomosis / Q000503:physiopathology / Q000601:surgery; D005260:Female; D005330:Fetofetal Transfusion / Q000453:epidemiology / Q000503:physiopathology* / Q000601:surgery; D006801:Humans; D010920:Placenta / Q000098:blood supply / Q000503:physiopathology* / Q000601:surgery; D011247:Pregnancy; D059285:Pregnancy, Twin; D015996:Survival Rate; D014430:Twins, Monozygotic
keywords: TTTS; amniodrainage; conservative; laser; progression; stage 1; survival; twin-to-twin transfusion syndrome