Objective: The primary objective of this study is to evaluate the time point of the luteoplacental shift in patients achieving pregnancy after transfer of cryopreserved embryos subsequently to IVF/ICSI cycles. Secondary objectives are to study the characteristics of the placental progesterone increase and its function as a predictor of the course and development of pregnancies and to study vaginal/endometrial microbiota at baseline and changes associated with shift into luteal phase and early pregnancy and how this potentially relates to pregnancy outcome. Study

Design: Prospective, multi-center, observational clinical cohort study. For the primary objective, data from a single center will be also be retrospectively analyzed. Study population: Female patients aged 18 to 45 years undergoing transfer of embryos after freezing and thawing 2PN oocytes or embryos. Interventions: Blood withdrawal, vaginal/endometrial swabs and endocrine and microbiom analyses. Study parameters/endpoints: The main parameter is time point of progesterone increase in pregnancy in relation to initial progesterone levels by pregnancy status. Secondary, slope and magnitude of placental progesterone increase and its relevance as a predictor for the course and development of pregnancies/babies. Furthermore, vaginal microbiota of women undergoing embryo transfer and of women in early pregnancy are parameter of this study.