Pregnancies achieved after transferring frozen morula/compact stage embryos

Objective: To report two cases of frozen embryo transfers in which embryos were frozen at the morula/ compact stage and pregnancies were achieved afte r transfer. Design: Case report. Setting: Private assisted reproductive program. Patient(s): Two women had transfer of embryos that were frozen at the morul a/compact stage. Intervention(s): Human morula/compact embryos were cryopreserved and transf erred after subsequent thaw. Main Outcome Measure(s): Embryo survival after thawing and subsequent pregn ancy outcome. Result(s): Three and five compact embryos were frozen on day 4 for two pati ents, respectively. In the first case, all three embryos survived after tha wing, and all were transferred. In the second patient, three of five embryo s survived after thawing, and those three surviving embryos were transferre d. Pregnancies were achieved in both patients. The first woman became pregn ant with twins and delivered two girls weighing 2,270 g and 2,071 g, respec tively. The second patient became pregnant with a singleton and delivered a boy weighing 2,837 g. Conclusion(s): Human embryos can be frozen and thawed in the morula/compact stage and achieve normal pregnancy. Advantages of embryo freezing/thawing at the morula/compact stage include the following: [1] compared with earlie r embryonic stage freezing, morula/compact-stage embryos provide better emb ryo selection and [2] it is easier and safer to perform assisted hatching o n compact-stage embryos when compared with those from other preimplantation stages. (C) 2001 by American Society for Reproductive Medicine.