Objective: To evaluate the need of P for endometrial preparation before cryopreserved embryo transfer (ET) in an artificial cycle.
Design: A case report.
Setting: : An IVF unit in a university hospital.
Patient(s): A 31-year-old woman treated in our IVF unit for secondary infertility due to severe oligoasthenospermia.
Intervention(s): Artificial preparation of the endometrium with estrogen (E) alone. Progesterone was added only after the cryopreserved embryos were transferred.
Main outcome measure(s): Plasma P levels, implantation, and pregnancy outcome.
Result(s): The pregnancy and delivery of a healthy fetus, resulting from a day 3 frozen-thawed embryo that was transferred to an endometrium without any previous P priming.
Conclusion(s): This unique case raises the question concerning the possibility that the putative "window of implantation" may be broader than previously thought, and that apposition and implantation can occur with minimal exposure to P.