Until now very little information exists regarding the early luteal serum progesterone profile after Human chorionic gonadotropin (hCG) trigger. This pilot study will help characterize the serum progesterone, 17-hydroxyprogesterone profiles in IVF patients and correlate progesterone, 17-Hydroxyprogesterone levels to ovarian follicles obtained after stimulation with exogenous gonadotropins.

The early luteal phase after IVF treatment is only scarcely studied. During IVF treatment the early luteinizing hormone (LH) activity deficit induced after ovarian stimulation with exogenous gonadotropins will be partly covered by the bolus of hCG used for triggering of final oocyte maturation due to the long half-life of hCG. In addition, the luteal phase will be covered by exogenous progesterone supplementation. After successful implantation the embryo itself will provide the supportive LH activity, securing the function of the corpora lutea. However, during the early luteal phase and peri-implantation, recent data suggest that an early-mid-luteal hCG/LH deficiency exists after hCG trigger during which the corpus luteum lacks an optimal stimulation. Furthermore, the early luteal progesterone profile in IVF differs significantly from the progesterone profile of the natural cycle, in which the peak is reached around the time of implantation. With this non-invasive trial, we wish to further explore the early luteal phase profiles of progesterone, 17-Hydroxyprogesterone and hCG in order to optimize current luteal phase support policies in IVF and hopefully increase ongoing pregnancy rates.

Inclusion Criteria:

• Freeze all cycle after hCG trigger
• Age 18 - 38
• BMI < 28kg/m2
• Normal ovarian reserve, defined by Anti-Mullerian Hormone (AMH) > 1.25 ng/ml or Antral Follicle Count (AFC) ≥ 6 measured within two months prior to stimulation start
• Receiving gonadotrophin releasing hormone (GnRH) antagonist co-treatment during ovarian stimulation
• Agreement to participate in the study, and to disclose any medical events to the investigator. The subject must be willing and able to comply with the protocol requirements for the duration of the study.
• Have given written informed consent with the understanding that the subject may withdraw consent at any time without prejudice to future medical care.

Exclusion Criteria:

• Previous poor response (≤ 3 oocytes) after high dose follicle stimulating hormone (FSH) stimulation
• Hyper-response defined as >20 follicles ≥ 14 mm
• Chronical medical conditions like Diabetes, Crohns disease, Thyroid disease, Hepatitis B and Sexually Transmitted Diseases Simultaneous participation in an interventional clinical trial.