Purpose: To present the occurrence of a monozygotic bichorionic twinning after the transfer of a single frozen/thawed embryo has undergone assisted zona hatching (AZH), using a non contact laser.
Methods: A 33-year-old woman who underwent single frozen embryo replacement (FER). Before transfer, the patient was treated with GnRH agonist and with substitutive therapy (estrogens and progesterone).
Conclusions: We are absolutely certain that we are reporting a monozygotic bichorionic pregnancy: a single frozen/thawed embryo was transferred and no concomitant spontaneous conception was possible. Moreover, molecular biology assessment for polymorphisms confirmed clinical findings. The possibility of the occurrence of a monozygotic bichorionic twinning after the transfer of a single frozen/thawed embryo should be borne in mind and its incidence will have to be studied further.