Adnexal masses detected during pregnancy require assessment integrating symptoms, ultrasound findings, and clinical course. We report the case of a 35-year-old pregnant woman who presented during the first trimester with a nine-day history of left iliac fossa pain. Initial assessment described a viable intrauterine pregnancy and a left adnexal cystic lesion measuring approximately 6 cm, clinically interpreted as a corpus luteum cyst. The patient remained hemodynamically stable and received analgesia and inpatient observation for three days, followed by outpatient monitoring. A follow-up image obtained at 13 weeks and 4 days showed a measurement of 5.70 cm and was labelled as a follicular cyst. According to the recorded clinical course, the lesion persisted at approximately 14 weeks and was no longer visualized at the 18-week assessment. The last reported follow-up was in the third trimester, without associated obstetric complications. The course was consistent with a presumed functional cyst; the available information does not establish its specific subtype conclusively. This case illustrates a favorable course during expectant management and highlights the importance of consistent diagnostic characterization and follow-up documentation of adnexal masses during pregnancy.

Keywords: Ovarian Cysts; Pregnancy; Ultrasonography; Case Reports.