title: Single-embryo transfer reduces clinical pregnancy rates and live births in fresh IVF and Intracytoplasmic Sperm Injection (ICSI) cycles: a meta-analysis.
abstract: BACKGROUND
  It has become an accepted procedure to transfer more than one embryo to the patient to achieve acceptable ongoing pregnancy rates. However, transfers of more than a single embryo increase the probability of establishing a multiple gestation. Single-embryo transfer can minimize twin pregnancies but may also lower live birth rates. This meta-analysis aimed to compare current data on single-embryo versus double-embryo transfer in fresh IVF/ICSI cycles with respect to implantation, ongoing pregnancy and live birth rates.
  
  
  METHODS
  Search strategies included on-line surveys of databases from 1995 to 2008. Data management and analysis were conducted using the Stats Direct statistical software. The fixed-effect model was used for odds ratio (OR). Fixed-effect effectiveness was evaluated by the Mantel Haenszel method. Seven trials fulfilled the inclusion criteria.
  
  
  RESULTS
  When pooling results under the fixed-effect model, the implantation rate was not significantly different between double-embryo transfer (34.5%) and single-embryo transfer group (34.7%) (P = 0.96; OR = 0.99, 95% CI 0.78, 1.25). On the other hand, double-embryo transfer produced a statistically significantly higher ongoing clinical pregnancy rate (44.5%) than single-embryo transfer (28.3%) (P < 0.0001; OR:2.06, 95% CI = 1.64,2.60). At the same time, pooling results presented a significantly higher live birth rate when double-embryo transfer (42.5%) (P < 0.001; OR: 1.87, 95% CI = 1.44,2.42) was compared with single-embryo transfer (28.4%).
  
  
  CONCLUSIONS
  Meta-analysis with 95% confidence showed that, despite similar implantation rates, fresh double-embryo transfer had a 1.64 to 2.60 times greater ongoing pregnancy rate and 1.44 to 2.42 times greater live birth rate than single-embryo transfer in a population suitable for ART treatment.
authors.affiliation: Center for Human Reproduction, Sao Paolo, Brazil. crh@crh.com.br
authors.forename: Ricardo L R
authors.initials: RL
authors.lastname: Baruffi
authors.forename: Ana L
authors.initials: AL
authors.lastname: Mauri
authors.forename: Claudia G
authors.initials: CG
authors.lastname: Petersen
authors.forename: Andréia
authors.initials: A
authors.lastname: Nicoletti
authors.forename: Anagloria
authors.initials: A
authors.lastname: Pontes
authors.forename: João Batista A
authors.initials: JB
authors.lastname: Oliveira
authors.forename: José G
authors.initials: JG
authors.lastname: Franco
mesh_terms: D001723:Birth Rate; D010064:Embryo Implantation; D004624:Embryo Transfer / Q000379:methods*; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D011247:Pregnancy; D018873:Pregnancy Rate; D016032:Randomized Controlled Trials as Topic; D020554:Sperm Injections, Intracytoplasmic