Ovarian hyperstimulation syndrome and assisted reproductive technologies: why some and not others?

Background: alpha(2)-Macroglobulin (alpha(2)M) is a multifactorial binding protein, found in follicular fluid, that is a naturally occurring inhibitor of vascular endothelial growth factor (VEGF). The aim of this study was to determine if there is a relationship between serum VEGF levels, alpha(2)M levels and the development of OHSS in hyperstimulated subjects undergoing IVF (those with 15 or more oocytes).

Methods: Venous blood was collected at the time of oocyte retrieval from subjects who yielded 15 or more oocytes. Serum samples were analysed for VEGF and alpha(2)M concentrations.

Results: There was no statistically significant difference in serum VEGF levels at the time of oocyte retrieval between hyperstimulated subjects who did and did not subsequently develop OHSS [3.95 (3.3-4.4) versus 3.85 (3.3-4.5); P = 0.79]. By contrast, the serum level of alpha(2)M was statistically significantly higher in the group of subjects who did not develop OHSS [2.27 (1.91-2.58) versus 1.67 (1.45-1.73)].

Conclusions: These results suggest that elevated alpha(2)M levels are associated with a decreased risk of developing OHSS. alpha(2)M may act by 'removing and inactivating' VEGF, with higher levels providing increased protection against the syndrome. alpha(2)M measurements may help to differentiate those for whom it is safe to proceed with embryo transfer from those for whom it is not, because of the risk of OHSS.