Objective: To explore a possible mechanism of the increasing incidence of monozygotic twins following assisted hatching of human embryos.
Design: Case report.
Setting: Clinical research center in a medical school teaching hospital.
Patient: A 37-year-old infertile woman with repeated IVF failures.
Intervention(s): Assisted hatching of the day 3 embryos using acidic Tyrode's solution.
Main outcome measure(s): The morphology of the zona-drilled embryos and the pregnancy outcome.
Result(s): After assisted hatching, a herniated blastomere through an oversized opening in the zona pellucida was found in one embryo. The transfer of two zona-drilled embryos resulted in a triplet pregnancy.
Conclusion(s): Large openings in the zona pellucida following chemically assisted hatching may cause premature hatching of the blastomeres and may be implicated in the occurrence of monozygotic twins.