This randomized trial will compare the efficacy of two different times of administration of medications for final oocyte maturation, commonly called a "trigger", in cycles of controlled ovarian stimulation (COS) for cycles in which all embryos will be cryopreserved ("freeze-all cycles").

This randomized trial will compare the efficacy of two different times of administration of medications for final oocyte maturation, commonly called a "trigger", in cycles of controlled ovarian stimulation (COS) for cycles in which all embryos will be cryopreserved ("freeze-all cycles").

1. The early trigger timing will be based on sonographic observation of at least three follicles reaching at least 17mm in diameter.
2. The delayed trigger timing will be based on at least three follicles reaching at least 22mm in diameter.

Inclusion Criteria:

1. Adult female at least 18 years of age and less than 35 years of age intending to undergo ovarian stimulation for a cycle of IVF with all embryos to be frozen that attain the blastocyst stage.
2. Anticipated at least normal ovarian response evidenced by at least 8 antral follicles observed on ultrasound or a serum level of at least 1.5 ng/ml AMH.
3. Ability read and understand English sufficiently to obtain informed consent.
4. Patients with prior IVF cycles are allowed, but no patient can undergo more than one cycle with oocyte collection under this study.

Exclusion Criteria:

1. Any cycle type that would preclude immediate culture to blastocyst stage (e.g. oocyte banking).
2. Any condition that, in the opinion of the physician or principal investigator, would place the patient at undue risk under this protocol or would otherwise make the protocol inappropriate for that subject.