RESUMEN
PURPOSE: Oocyte donation is a well-established method of assisted reproduction for women with irreversible infertility and with previous implantation failures after in vitro fertilization. Although the pregnancy rates are very high, sometimes implantation does not occur even after various attempts. We report the first two cases of transfer of zona-free blastocysts in oocyte donation cycles that developed to normal pregnancies and births. METHODS: The patients had undergone three previous standard oocyte donation cycles with failure of implantation. Endometrium preparation was performed after suppression of the pituitary function, with E2 valerate and Progesterone at the day of oocyte retrieval. Normally fertilized embryos were cultured in Earle's culture medium until Day 3 and in S2 medium until Day 5. For each patient, the zonae of two fully expanded blastocysts were enzymatically removed with 0.5% pronase. Zona-free blastocysts were transferred for the patients 2 h later. RESULTS: On Day 12 after transfer, pregnancies were confirmed with elevated serum levels of beta hCG. A gestational sac with a foetal heart beat was seen by ultrasound 15 days later, in each patient. Normal healthy babies were born at 38 and 39 weeks of pregnancy. CONCLUSIONS: This is the first report of successful pregnancies and births after oocyte donation and transfer of zona-free blastocysts in human. It not only shows the feasibility of the treatment but also opens a new alternative for the patients with repetitive implantation failure after OD cycles.