203: The effects of vanishing twin on perinatal outcomes of the co-twin: a systematic review with meta-analysis

Abstract

To review literature about perinatal outcomes of pregnancies complicated with vanishing twin. A search in PubMed, Embase, Cochrane, reference lists was performed to find articles comparing singletons after vanishing twin (SAVT) with singletons from start (SFS). Key words: vanishing twin, singleton, in vitro fertilization. Inclusion criteria: comparative studies of SAVT vs. SFS, data reported as proportional rates. Exclusion criteria: twin pregnancies, case reports personal communication. PRISMA guidelines were followed. Inter-studies heterogeneity was tested and a random effects model was generated if heterogeneity was >25%. For dichotomic variables, pooled odds ratio and 95%ConfidenceInterval (OR 95%CI) were considered statistically significant if 95%CI did not encompass 1. For continuous variables, the Weight Mean Difference ratio and 95%ConfidenceInterval (WMD 95%CI) were considered statistically significant if 95%CI did not encompass 1. From 4 articles, 393 SAVT were compared with 2629 SFS. All pregnancies were conceived following in-vitro fertilization and the vanishing twin was observed in the first trimester in all cases. Gestational age at delivery was similar between the two groups (WMD: -0.84; 95%CI: -1.84/0.16), as well as preterm delivery rates (SAVT: 19.2%; SFS: 18.6%; OR: 0.93; 95%CI: 0.17-5.24). Birth weight did not differ between the two groups (WMD: -169.42; 95%CI: -424.28/85.43), although the rates of birth weight <1500 g was higher in SAVT (12.3%) than SFS (0.3%; OR: 17.83; 95%CI: 1.48-21.4). Stillbirth was more frequent in SAVT (6.2%) than SFS (4.0%; OR: 1.95; 95%CI: 1.19-3.19). There is lack of information about neonatal morbidity. The detection of a vanishing twin is associated with a higher risk of stillbirth and low birth weight. Because gestational age at delivery and preterm rates are similar between SAVT and SFS, it is likely that fetal growth of singletons is impaired soon after vanishing of the co-twin.