Impact of a Previous CS on the Ongoing Pregnancy Rate in Single Euploid Frozen Embryo Transfer (ET)

Inclusion Criteria: \- All participants undergoing a single euploid FET, independent of the endometrial preparation approach Exclusion Criteria: * Intracavitary fluid during preparation for FET * Known anomaly of the uterus or the adnexae (e.g.: fibroids, polyps, hydrosalpinx, endometriosis, adenomyosis) * Embryo which was biopsied on day 7 * Poor quality embryo which was transferred (Gardner criteria: AC / BC / CB, biopsied on day 6 and CC embryos from both, day 5 and day 6 biopsies, classified as "poor" quality embryos) * History of recurrent abortion * Antiphospholipid syndrome / autoimmune diseases