FLT1 and ovarian hyperstimulation syndrome: For the prediction of OHSS, several risk factors have been identified, including young age (<35 years old), polycystic ovary syndrome (PCOS), prior occurrences of OHSS, increased numbers of medium- and large-sized follicles, elevated serum anti-Mullerian hormone (AMH) and estradiol (E2) levels and high levels of soluble vascular endothelial growth factor receptor 1/sFlt1 in follicular fluid (11–14).