A unique case of diagnosis of a heterotopic pregnancy at 26 weeks - case report and literature review.

Background: Heterotopic pregnancy (HP) is a rare condition when at least two pregnancies are present simultaneously at different implantation sites and only one located in the uterine cavity. The majority of cases are diagnosed in the first trimester.
Case Presentation: We present a unique case of HP diagnosed at 26 weeks of spontaneous pregnancy in a patient without any relevant risk factors. We performed an extensive review of HP cases from MEDLINE (PUBMED) published in English between 2005-2019 to prove this case's uniqueness. A 24-year-old woman presented because of threatened preterm birth. Despite treatment, pain aggravated, without progression of labor. An emergency ultrasound exam revealed free fluid in the abdominal cavity. Suspicion of active bleeding prompted the medical team to perform an exploratory laparotomy. The surgery team found a ruptured heterotopic pregnancy. This was an unexpected cause of nontraumatic hemoperitoneum at such advanced gestational age. The postoperative period was uneventful, and the intrauterine pregnancy continued to term. The final review included 86 out of 124 records. A total number of 509 cases were identified, but not all of them had complete data. The maximum reported gestational age at the time of diagnosis was 16 weeks of pregnancy, while our case became symptomatic and was diagnosed at 26 weeks of pregnancy.
Conclusions: Regardless of pregnancy age, HP can be a cause of hemoperitoneum, and it should be included in the differential diagnosis of acute abdomen in the second trimester.