Pregnancy and birth outcomes of single versus multiple embryo transfer in gestational surrogacy arrangements: a systematic review and meta-analysis.

Multiple embryo transfer (MET) is associated with both an increased risk of multiple pregnancy and of live birth. In recent years, MET has become standard practice for most surrogacy arrangements. There is limited review of the use of MET versus single embryo transfer (SET) in surrogacy practice. The present review systematically evaluated the pregnancy outcomes of surrogacy arrangements between MET versus SET among gestational carriers. A systematic search of five computerized databases without restriction to the English language or study type was conducted to evaluate the primary outcomes: (i) clinical pregnancy; (ii) live delivery; and (iii) multiple delivery rates. The search returned 97 articles, five of which met the inclusion criteria. The results showed that clinical pregnancy (RR = 1.21, 95% CI: 1.06-1.39, n  =  5, I2 = 41%), live delivery (RR = 1.29, 95% CI: 1.10-1.51, n  =  4, I2 = 35%) and multiple delivery rates (RR = 1.42, 95% CI: 6.58-69.73, n  =  4, I2 = 54%) were statistically significantly different in MET compared to SET. Adverse events including miscarriage, preterm birth and low birthweight were found following MET. Our findings support the existing evidence that MET results in multiple pregnancy and subsequently more adverse outcomes compared to SET. From a public health perspective, SET should be advocated as the preferred treatment for gestational carriers.