Natural Pregnancy Following Oocyte Retrieval in a Luteal-Phase Progestin-Primed Ovarian Stimulation (PPOS) Protocol With Concurrent Blastocyst Cryopreservation: A Case Report.

Ovarian stimulation is used in assisted reproductive technology to help infertile couples achieve pregnancy. Luteal-phase stimulation with progestin-primed ovarian stimulation (PPOS) is a practical approach, as it involves oral medication with fewer daily injections compared to gonadotropin-releasing hormone (GnRH) agonist or GnRH antagonist protocols. Unintended pregnancy during ovarian stimulation or after oocyte pick-up (OPU) is rare but possible. We present the case of a 38-year-old patient with secondary infertility, known to have endometriosis, chronic inflammatory demyelinating polyneuropathy, and low ovarian reserve. She initially underwent ovarian stimulation with an antagonist protocol, which was later switched to luteal-phase PPOS to improve synchronization. For ovulation induction to initiate luteal-phase stimulation, the patient received human chorionic gonadotropin (hCG). A pregnancy test performed during ovarian stimulation yielded a result consistent with exogenous hCG administration. On the day of OPU, a corpus luteum was observed in the right ovary, and two follicles were present in the left ovary. OPU resulted in the retrieval of one oocyte, which developed into a blastocyst and was subsequently cryopreserved. A natural pregnancy was detected by hCG testing 10 days after OPU, prompted by a delayed menstrual cycle and the corpus luteum observed during OPU. Transvaginal ultrasound confirmed an intrauterine pregnancy with a positive fetal heartbeat. This case highlights the importance of considering the possibility of pregnancy even after luteal-phase PPOS and OPU, taking into account both the patient's clinical context and laboratory findings.