Obese and underweight women have an increased risk of miscarriage, and hormonally substituted FET is associated with an even higher MR.

The presence of ≥1 top quality embryo at any step of the freezing and thawing process increases the chance of pregnancy. The data do not support the freezing of all embryos for transfer in order to improve the outcome. A top quality embryo transferred in FET may even have the same potential as in a fresh cycle. On the contrary, LBR in the group with no top quality embryos frozen was quite low (10.4%), raising the question of whether a re-evaluation of freezing criteria is necessary to avoid costly treatments with a low success rate.

The eSET policy can be applied also to patients aged 36-39 years, reducing the risk of multiple birth and increasing the safety of assisted reproduction technique (ART) in this age group.

STUDY QUESTION What is good practice in ultrasound (US), and more specifically during the different stages of transvaginal oocyte retrieval, based on evidence in the literature and expert opinion on US practice in ART? SUMMARY ANSWER This document provides good practice recommendations covering technical aspects of US-guided transvaginal oocyte retrieval (oocyte pick up: OPU) formulated by a group of experts after considering the published data, and including the preparatory stage of OPU, the actual procedure and post-procedure care. WHAT IS KNOWN ALREADY US-guided transvaginal OPU is a widely performed procedure, but standards for best practice are not available. STUDY DESIGN, SIZE, DURATION A working group (WG) collaborated on writing recommendations on the practical aspects of transvaginal OPU. A literature search for evidence of the key aspects of the procedure was carried out. Selected papers (n = 190) relevant to the topic were analyzed by the WG. PARTICIPANTS/MATERIALS, SETTING, METHODS The WG members considered the following key points in the papers: whether US practice standards were explained; to what extent the OPU technique was described and whether complications or incidents and how to prevent such events were reported. In the end, only 108 papers could be used to support the recommendations in this document, which focused on transvaginal OPU. Laparoscopic OPU, transabdominal OPU and OPU for IVM were outside the scope of the study. MAIN RESULTS AND THE ROLE OF CHANCE There was a scarcity of studies on the actual procedural OPU technique. The document presents general recommendations for transvaginal OPU, and specific recommendations for its different stages, including prior to, during and after the procedure. Most evidence focussed on comparing different equipment (needles) and on complications and risks, including the risk of infection. For these topics, the recommendations were largely based on the results of the studies. Recommendations are provided on equipment and materials, possible risks and complications, audit and training. One of the major research gaps was training and competence. This paper has also outlined a list of research priorities (including clarification on the value or full blood count, antibiotic prophylaxis and flushing, and the need for training and proficiency). LIMITATIONS, REASONS FOR CAUTION The recommendations of this paper were mostly based on clinical expertise, as at present, only a few clinical trials have focused on the oocyte retrieval techniques, and almost all available data are observational. In addition, studies focusing on OPU were heterogeneous with significant difference in techniques used, which made drafting conclusions and recommendations based on these studies even more challenging. WIDER IMPLICATIONS OF THE FINDINGS These recommendations complement previous guidelines on the management of good laboratory practice in ART. Some useful troubleshooting/checklist recommendations are given for easy implementation in clinical practice. These recommendations aim to contribute to the standardization of a rather common procedure that is still performed with great heterogeneity. STUDY FUNDING/COMPETING INTEREST(S) The meetings of the WG were funded by ESHRE. The other authors declare that they have no conflict of interest. TRIAL REGISTRATION NUMBER NA. ESHRE Pages content is not externally peer reviewed. The manuscript has been approved by the Executive Committee of ESHRE.

This study shows that eSET with cryopreservation is more effective and less expensive than DET and should be adopted as a treatment of choice.