Objective: To evaluate the teratogenic or fetal risk of a long-acting GnRH agonist (GnRH-a) triptoreline acetate (Decapeptyl; Ipsen-Biotech, Inc., Paris, France), inadvertently administrated in the first weeks of pregnancy. Design: Prospective follow-up of exposed pregnancies and case reports. Setting: Teratology information service of a public hospital and pharmacovigilance department of the firm. Patients: Inadvertent pregnant women receiving a treatment, mainly for endometriosis or IVF. Interventions: Case by case, individual estimations of the risks have been provided. Main Outcome Measure: Each pregnancy issue has been analyzed. Results: No teratogenic or fetal toxic effect has been noted. Conclusion: No specific hazard has been observed among newborns after inadvertent exposures to a GnRH-a during the first 20 weeks of pregnancy.