All women undergoing pituitary down-regulation before planned in-vitro fertilization (IVF) treatment in two IVF units were studied to assess the risks of and to pregnancies occurring inadvertently when gonadotropin-releasing hormone agonists (GnRHa) were used to achieve pituitary desensitization during the luteal phase prior to planned IVF treatment. In 2670 cycles, 25 women conceived (0.9% of cycles). Of these, three resulted in pre-clinical abortions (12%) but there were no clinical abortions, and 22 have ended with live births at term of apparently normal infants. Collation of these and other published data suggest that pregnancy outcome is not adversely affected by GnRHa administration in the luteal phase of the conception cycle.