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FeSe, despite being the structurally simplest compound in the family of iron-based superconductors, shows an astoundingly rich interplay of physical phenomena including nematicity and pressure-induced magnetism. Here, we present a microscopic study of these two phenomena by high-energy x-ray diffraction and time-domain Mössbauer spectroscopy on FeSe single crystals over a wide temperature and pressure range. The topology of the pressure-temperature phase diagram is a surprisingly close parallel to the well-known doping-temperature phase diagram of BaFe2As2 generated through partial Fe/Co and Ba/Na substitution. In FeSe with pressure p as a control parameter, the magneto-structural ground state can be tuned from "pure" nematic -paramagnetic with an orthorhombic lattice distortion -through a strongly coupled magnetically ordered and orthorhombic state to a magnetically ordered state without an orthorhombic lattice distortion. The magnetic hyperfine field increases monotonically over a wide pressure range. However, the orthorhombic distortion initially decreases under increasing pressure, but is stabilized by cooperative coupling to the pressure-induced magnetic order. Close to the reported maximum of the superconducting critical temperature Tc (occuring at p = 6.8 GPa), the orthorhombic distortion suddenly disappears and FeSe remains tetragonal down to the lowest temperature measured. Analysis of the structural and magnetic order parameters suggests an independent origin of the structural and magnetic ordering phenomena, and their cooperative coupling leads to the similarity with the canonical phase diagram of iron pnictides. arXiv:1803.09449v1 [cond-mat.supr-con]

STUDY QUESTION Is a dual ovulation trigger with a combination of GnRH agonist (GnRHa) and hCG superior to single hCG and/or single GnRHa trigger in improving treatment outcomes in advanced-age women (aged ≥ 35 years) undergoing IVF/ICSI treatment? SUMMARY ANSWER Co-administration of GnRHa and hCG as a dual trigger increases the number of good-quality embryos but it is not associated with a higher number of oocytes retrieved, compared with single hCG or GnRHa trigger. WHAT IS KNOWN ALREADY Many studies have demonstrated that a dual trigger has positive impact on oocyte maturation, retrieval rate and pregnancy rate without increasing the risk of ovarian hyperstimulation syndrome (OHSS) in some groups of IVF patients, when compared with single hCG trigger. Few studies have however been conducted to compare a dual trigger with a single GnRHa trigger, and insufficient evidence exists to support which trigger can achieve the best outcomes in IVF patients aged ≥35 years. STUDY DESIGN, SIZE, DURATION This was an open-label randomized controlled trial of 510 participants conducted at single reproductive medical center from January 2019 to December 2021. After a sample size calculation performed by retrospectively analyzing our previous clinical data, we planned to recruit 170 patients in each group and 510 patients in total for the study. PARTICIPANTS/MATERIALS, SETTING, METHODS Women aged ≥35 years undergoing IVF/ICSI treatment, receiving a non-pituitary down-regulation protocol, and with low risk of OHSS, were enrolled in this trial. On the trigger day, patients were randomized into three groups: hCG alone (who received 6000 IU of hCG), GnRHa alone (who received 0.2 mg of triptorelin) and dual trigger (who received 0.2 mg of triptorelin plus 2000 IU of hCG) groups. The primary outcome parameter was the number of retrieved oocytes. The secondary outcome parameters included, among others, the number and rates of mature oocytes, two pronuclei (2PN) embryos and good-quality embryos, as the rates of OHSS, clinical pregnancy, miscarriage and live birth. MAIN RESULTS AND THE ROLE OF CHANCE There were no significant differences in the baseline demographic characteristics among the three groups. The dual trigger was associated with a higher retrieval rate (87.9% vs 84.1% in the hCG group, P = 0.031; 87.9% vs 83.6% in the GnRHa group, P = 0.014). However, the number of retrieved oocytes in the dual trigger group was comparable with those in the hCG group (4.08 ± 2.79 vs 3.60 ± 2.71, P = 0.080) and the GnRHa group (4.08 ± 2.79 vs 3.81 ± 3.38, P = 0.101); comparable data between the groups were also found when analyzing the number of 2PN embryos and the 2PN rate. In the dual trigger group, the numbers of good-quality embryos and viable embryos were both significantly higher than in the hCG group (1.74 ± 1.90 vs 1.19 ± 1.45, P = 0.016 and 2.19 ± 2.11 vs 1.56 ± 1.66, P = 0.008, respectively) and the GnRHa group (1.74 ± 1.90 vs 1.20 ± 1.67, P = 0.003 and 2.19 ± 2.11 vs 1.45 ± 1.75, P = 0.001, respectively). Pregnancy outcomes after fresh embryo transfer (ET) were comparable between the groups. The live birth rate and ongoing pregnancy rate after frozen ET in the dual trigger group were significantly higher than those in the GnRHa group (32.6% vs 14.1%, P = 0.007 and 34.8% vs 17.6%, P = 0.013, respectively), but not superior to those in the hCG group (32.6% vs 27.9%, P = 0.537 and 34.8% vs 27.9%, P = 0.358, respectively). LIMITATIONS, REASONS FOR CAUTION Women of advanced age are quite a heterogeneous population and overlap with poor ovarian responders or patients with diminished ovarian reserve. We therefore could not entirely exclude selection biases or confounding factors. This study was also not a double-blinded trial; the patients in the GnRHa and dual trigger groups could have been affected by the placebo effect. WIDER IMPLICATIONS OF THE FINDINGS The results of this study suggest that in advanced-age women with low risk of OHSS, a dual trigger or even a single hCG trigger may be a better choice than a single GnRHa trigger. STUDY FUNDING/COMPETING INTEREST(S) This study was supported by the Shanghai Municipal Health Commission of Science and Research Fund (20184Y0289). The authors declare no conflict of interest. TRIAL REGISTRATION NUMBER This trial was registered in the Chinese Clinical Trial Registry (ChiCTR-1800016285). TRIAL REGISTRATION DATE 24 May 2018 DATE OF FIRST PATIENT’S ENROLMENT 2 January 2019

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