A recent Spanish study showed a 7% increase in birth rates when two embryos were transferred together. When only one embryo was implanted, the survival to birth rate was 76%, vs 83% for a twin pregnancy.
The study, published in the January 2012 Obstetrics and Gynecology, introduced the concept of “embryo assistance” where the stronger embryo may help the weaker embryo survive. This study was based on data from 1,159 single and 523 twin pregnancies, and the difference in birth rates was more prounounced in women over 33 years of age.
Many experts are discounting this concept, saying that there is just not yet enough data to support the theory. It flies in the face of new trends encouraging transferring one embryo at a time.
The ASRM suggests not transferring more than two embryos in women under 35, due to the increased risks of a multiple pregnancy - both for the mother and fetuses.
Many of the leading IVF clinics are having high success rates and encouraging elective single embryo transfers (eSET), particularly for younger patients or those using donor eggs where the egg and embryo quality should be overall a higher quality.