Cryo-thawed embryo transfer: natural versus artificial cycle. A non-inferiority trial.(ANTARCTICA trial)

In this randomized, multi-centre, non-inferiority trial we aim to test the hypothesis that there is no significant difference in live birth rates between patients undergoing NC-FET versus AC-FET. The primary outcome will be live birth rate per embryo transfer procedure. Secondary outcomes will be ongoing and clinical pregnancy rate, cancellation rate, (serious) adverse events and cost-efficiency. Based on a live birth rate of 20% and a minimal clinical important difference of 7,5% (one-sided alpha 2,5%, beta 20%) a total of 1150 patients will be needed. Analyzes will be performed using both per protocol as well as intention to treat analyses.This prospective, randomized, non –inferiority trial aims to address the hypothesis that there is no significant difference in live birth rates between patients undergoing NC-FET versus patients undergoing AC-FET. Moreover it addresses cost-efficiency as well as the perceived burden of both treatments.Netherlands trial register (NTR): 1586In Vitro Fertilization (IVF) or Intra Cytoplasmatic Sperm Injection (ICSI) treatment cycles often produce more embryos than can be transferred during the fresh treatment cycle. Moreover, in some patients embryo transfer is postponed for medical reasons (e.g. ovarian hyperstimulation syndrome). Cryopreservation of these embryos provides both physicians and patients a safe, successful and presumably cost-efficient option [1-3]. Recent development and implementation of single embryo transfer strategies in IVF and IVF -ICSI programs has increased the importance of successful frozen thawed embryo transfer (FET) programs. Critical for a successful FET program is synchronization between the endometrial development and the embryo [4-7]. To achieve this, FET requires extensive preparation, timing and planning. In recent years, several methods for endometrium preparation have been developed.In natural cycle FET (NC-FET) planning of embryo thawing and transfer requires the identification of a period of op