Michelle Emblenton, a biochemist at inviTRA, talks about when ovarian hyperstimulation syndrome, or OHSS, happens:
Ovarian hyperstimulation syndrome can occur following the ovarian stimulation of an assisted reproduction treatment. The HCG hormone is given usually to trigger the final maturation of the egg cells prior to the egg retrieval. hCG is actually the main trigger cause of OHSS, as it increases the vascular permeability of the cells. This basically means that the spaces between cells in the ovary can become filled with fluid. Early onset, OHSS can occur up to a week after the administering of the HCG to mature the follicles. There is also a late onset OHSS and this is due to, if pregnancy is achieved, the hormone hCG will actually be produced by the body as part of the pregnancy, leading to increased levels of this hormone.
