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.