26% of all ART cycles performed in the USA in 2003 (CDC data) are frozen embryo transfers (FET) and transfer of embryos resulting from egg donation (ED) to recipients. The typical protocol used to prepare a recipient for ET involves GnRH agonist (Lupron, Tap Pharmaceuticals) to down regulate the patient. A GnRH antagonist, such as Cetrotide (EMD Serono), is comparable to GnRH agonist and FDA approved to prevent spontaneous ovulation with ART treatment, and its usage decreases significantly the number of injections that the patient receives with treatment. The working hypothesis for this study is that the GnRH antagonist (Cetrotide) can be used instead of an agonist to achieve effective down regulation in FET and ED cycles. Presumably, patients will prefer Cetrotide over Lupron because of the markedly fewer injections required.

Inclusion Criteria:

• History of infertility before cryopreserving the embryos or inability to conceive from her own oocytes (based on age and/or a serum FSH > 15 IU/L).
• Any patient desiring to become pregnant as a result of transferring frozen-thawed embryos generated using her own or donor oocytes.
• Subject is in good health as determined by the Investigator on the basis of medical history, physical examination and laboratory screening tests.
• A negative pregnancy test prior to starting treatment with estrogens.

Exclusion Criteria:

• Women with a history of liver and/or kidney disease
• Hypertension: systolic pressure over 180 mm Hg or diastolic pressure over 105 at any study visit, measured twice 6 hours apart despite active treatment for hypertension.
• Liver function tests of two times than the upper limit of normal
• Women with active sever endometriosis.