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A rise of the serum level of von Willebrand factor occurs before clinical manifestation of the severe form of ovarian hyperstimulation syndrome.

BACKGROUND
Ovarian hyperstimulation syndrome (OHSS) appears to be caused by increased capillary permeability in the vascular endothelial cells. Such cells secrete excess amounts of von Willebrand factor (vWF), a large adhesive glycoprotein.


METHODS
We retrospectively evaluated the circulating levels of vWF and of vascular endothelial growth factor (VEGF) twice, on the days of oocyte retrieval and embryo transfer, in 46 women who developed early-onset OHSS.


RESULTS
Nineteen, 14, and 13 women developed mild, moderate, and severe OHSS, respectively. Inconsistent changes were observed in the VEGF during oocyte retrieval and embryo transfer. However, the net increase in serum vWF during that period showed an increase in absolute value at the time of embryo transfer that paralleled an increase in the severity of OHSS. That is, in mild OHSS, the serum vWF increased from 140 +/- 44 to 164 +/- 28%; in moderate OHSS, it increased from 113 +/- 47 to 186 +/- 22%; and in severe OHSS, it increased from 120 +/- 35 to 274 +/- 63%. All 9 women with a vWF level > 230% at embryo transfer developed severe OHSS, while 9 of 13 women with severe OHSS exhibited a vWF > 230% at embryo transfer.


CONCLUSION
The results suggest that a rise of the serum level of vWF occurs prior to clinical manifestation of OHSS in patients with severe OHSS but not in patients with mild OHSS.