Objective: To report a case of monozygotic twinning after atypical hatching of a human blastocyst.
Design: Case report.
Setting: University-based IVF program.
Patient(s): A 33-year-old woman with tubal sterility.
Intervention(s): Embryo transfer of a human blastocyst with atypical hatching.
Main outcome measure(s): Development to the blastocyst stage, hatching process, follow-up of pregnancy.
Result(s): Development of a monozygotic dichorial pregnancy.
Conclusion(s): First report of an atypical hatching of a human blastocyst leading to dichorial monozygotic twinning.