In the literature, the risk of moderate to severe OHSS is 3 to 6% and reaches 31% in high risk populations 9 days after oocyte triggering with hCG. Many studies report no or a markedly decreased risk of OHSS after triggering ovulation with a GnRH agonist. However, criteria to define OHSS are rarely explained and OHSS itself is not thoroughly asserted. It is well known that OHSS is associated with hypercoagulability. However, no study after triggering with a GnRH agonist assessed haemostasis in these high-risk patients with high circulating estradiol levels.