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<0.0001; OR: 1.95; 95% CI: 1.41-2.71). Birth weight differed between groups.

Conclusion: ART twins carry increased risk of adverse outcomes. UST are at higher risk of perinatal death, although further studies are needed to assess whether chorionicity impacts on neonatal outcomes after ART.