Heterotopic pregnancy in a patient with severe hypothyroidism: a rare case report.

Heterotopic pregnancy (HP), defined as the coexistence of intrauterine and extrauterine gestations, is a rare but potentially life-threatening condition. Its incidence is estimated at 1 in 30 000 spontaneous pregnancies, while assisted reproductive technology (ART) markedly increases prevalence, reaching up to 1% after in vitro fertilization (IVF). Diagnosis is challenging since nearly half of patients remain asymptomatic until rupture, and the presence of an intrauterine pregnancy may mask the ectopic component. We report a case of HP in a 25-year-old woman with severe untreated hypothyroidism post-thyroidectomy, who conceived spontaneously without ART. She presented with hemoperitoneum from a ruptured interstitial pregnancy and underwent emergency laparotomy with salpingectomy. Despite initial preservation of the intrauterine pregnancy, fetal demise occurred later. This rare association underscores the importance of maintaining a high index of suspicion for HP even in the absence of risk factors and raises questions about whether thyroid dysfunction may contribute to abnormal implantation.