Potential risk of monochorionic dizygotic twin blastocyst formation associated with early laser zona dissection of group cultured embryos.

OBJECTIVE To document the risk of in vitro monochorionic dizygotic twin formation in the implementation of a program of blastocyst biopsy with preimplantation genetic screening (PGS). DESIGN Case report. SETTING Private infertility laboratory. PATIENT(S) Prospective PGS patients with intracytoplasmic sperm injection-derived, group-cultured blastocysts over a 3-year period. INTERVENTION(S) Group culture in Global medium (Life Global) to optimize blastocyst formation of zygotes produced for blastocyst biopsy for PGS (n ≤ 8 embryos/25 μL droplet), and laser zona dissection (LZD) of all day-3 cleaved embryos to promote pre-expansion trophectodermal extrusion at the blastocyst stage (i.e., premature hatching). MAIN OUTCOME MEASURE(S) Blastocyst formation and quality grading on days 5 and 6 of in vitro culture for the vitrified embryo transfer of single or dual euploid blastocysts. RESULT(S) Over 3,000 blastocysts were produced in vitro. On two separate occasions, complete trophectodermal amalgamation was observed between two hatching blastocysts. Vitrified single-euploid blastocyst transfers efficiently implanted and established clinical pregnancies similar to dual-euploid blastocyst transfers, without the risk of twin formation. CONCLUSION(S) The amazing occurrence of monochorionic dizygotic twin formation has now been documented in vitro, supporting the theory that assisted reproductive technology may facilitate this rare perinatal condition. Furthermore, we have provided clinical evidence that the transfer of a single-euploid blastocyst can optimize a patient's pregnancy success while reducing potentially undesirable conditions associated with monochorionic twin pregnancies.