Ultrarapid cryopreservation of human embryos: experience with 1,582 embryos

Objectives: To demonstrate the effectiveness of ultrarapid cryopreservation inhuman embryos. Design: Retrospective study. Setting: An IVF unit of a medical center. Patient(s): All cases received ultrarapid freezing (URF) of embryos and fro zen embryo transfer. Intervention(s): Embryos were placed in phosphate-buffered saline (PB1) + 2 0% maternal serum (MS) for 5 minutes. Embryos were loaded to the straws con taining PB1 + MS + 0.25 M sucrose (SUC) + 3.5 M dimethyl sulfoxide for 3 mi nutes, and then were stored in a liquid nitrogen tank. Embryos were thawed in a 37 degrees C water for 6 seconds and then cultured in PB1 + MS + SUC f or 10 minutes. Embryos were transferred into PB1 + MS for 5 minutes and wer e transferred into patients. Main Outcome Measure(s): The embryo grades before and after URF, the surviv al and transferred embryo numbers, and the pregnancy and abortion rates wer e analyzed. Result(s): A total of 1,582 embryos were thawed, of which 1,273 (80.5%) emb ryos were transferred and 1,032 (65.2%) embryos survived with greater than or equal to 50% intact blastomere. The embryo numbers with grade I or II be fore and after freezing and thawing were 1,110 (70.2%) and 790 (50.0%). The mean embryo numbers per transfer was 5.0. Twenty-eight pregnancies (11.4% per transfer) were established, which included 5 miscarriages, 1 ectopic pr egnancy, 4 preterm and 18 term deliveries. Conclusion(s): Ultrarapid freezing is worthy of reconsideration for embryo cryopreservation. (C) 1999 by American Society for Reproductive Medicine.