1. Single blastocyst transfer: a prospective randomized trial
David K Gardner, D.Phil., Eric Surrey, M.D., Debra Minjarez, M.D., Annette Leitz, L.P.N., John Stevens, B.S., William B Schoolcraft, M.D. 
Fertility and Sterility 
Volume 81, Issue 3, Pages (March 2004)
DOI: /j.fertnstert

2. FIGURE 1
In vitro fertilization outcome after the transfer of either one or two blastocysts. Dark bars represent the transfer of a single blastocyst (group I); open bars represent the transfer of two blastocysts (group II). Implantation and pregnancy rates were not statistically different between the two groups of patients. There were no twins in group I in contrast to 47.4% twins in group II. The biochemical pregnancy rate was equivalent between the two groups (group I, 12.5%; group II, 5%).
Gardner. Single blastocyst transfer.Fertil Steril 2004.
Fertility and Sterility  , DOI: ( /j.fertnstert )