A Clinical Conundrum of Unilateral Ovarian Agenesis With Associated Ipsilateral Absence of the Fallopian Tube.

Unilateral ovarian agenesis (UOA) is a rare condition that is often associated with the ipsilateral absence of the fallopian tube. We report the case of a 31-year-old woman, G3P1+1, at approximately 5 weeks' gestation, who initially presented with left iliac fossa pain, raising concern for a possible ectopic pregnancy versus miscarriage. The differential diagnosis was later expanded to include heterotopic pregnancy with left haematosalpinx, based on early imaging findings and a suboptimal decline in serial serum beta-human chorionic gonadotropin (β-hCG) levels. As a result, an urgent laparoscopic evaluation with evacuation of retained products of conception (ERPOC) was performed, which confirmed the absence of the left ovary and fallopian tube, along with an intrauterine anembryonic pregnancy. This case highlights the need for a high index of suspicion when imaging findings and β-hCG trends do not correlate, and underscores the importance of a systematic laparoscopic examination for definitive diagnosis.