'Controlled' ovarian stimulation: who's kidding who?

In modern fertility practice, much time and energy is devoted to controlling ovarian stimulation. Is this effort well directed? Does monitoring and dose adjustment prevent complications and improve outcomes? Or does it just provide clinicians with a false sense of security and power to influence ovarian function? Monitoring ovarian stimulation can identify excess response, and enable the clinician to prevent complications of hyperstimulation by terminating the cycle. However, subtle interventions such as dose adjustment to monitored response have little impact on outcomes. Poor responders are frequently subjected to increased doses of gonadotropins in the hope of improving chances of undergoing oocyte pick up and achieving pregnancy. However, the evidence supporting this approach is scarce. In the context of ovarian stimulation for IUI, interventions aimed at limiting response have little impact on the risk of multiple pregnancies. Why is the ovarian response so difficult to control? While recent studies suggest that batch variation in the bioactivity of gonadotropin preparations may be partially to blame, it is becoming increasingly evident that patient-related factors, rather than doctor-controlled factors are the primary determinants of outcome from ovarian stimulation.