Neonatal outcomes of assisted and naturally conceived twins: systematic review and meta-analysis.

OBJECTIVE: To review the neonatal outcomes of assisted reproductive technique (ART) vs. naturally conceived (NC) twins. METHODS: A search in PubMed, Medline, EMBASE, and Cochrane library was performed (January 2000-September 2010). Articles reporting outcomes of ART vs. NC twins were classified in controlled and non-controlled studies. A sub-group was limited to unlike sex twins (UST). The MOOSE guidelines were followed. A randomized model was generated if inter-studies heterogeneity was >25%. Inter-group comparison was significant if P<0.05. RESULTS: Thirteen articles were reviewed. In non-controlled studies, outcomes were equal between groups, except for cesarean section rates (ART: 71.8%; NC: 49.6%; P<0.0001; OR: 2.34; 95% CI: 1.55-3.54). Similar results were obtained in controlled studies, except for higher rates of preterm delivery in ART (55%) than in NC (53%) twins (P=0.03; OR: 1.30; 95% CI: 1.03-1.65). UST differed with regard to preterm delivery (ART: 58.6%; NC: 49.5%; P<0.0001; OR: 1.51; 95% CI: 1.25-1.83), and perinatal death (ART: 3.6%; NC: 1.8%; P