The findings of these studies and resulting statistics may be extremely devastating to the women and their families who had struggled to become pregnant, and have finally given birth only to find that the fertility drug they were given caused their baby to suffer from a severe or deadly birth defect. long-term side effects of tamoxifen Sometimes an ultrasound is performed mid-cycle to assess your response to this medication, and to determine the number of eggs that are going to be ovulated that month.