Research progress in pregnancy of unknown location

Pregnancy of unknown location (PUL) refers to a positive human chorionic gonadotropin (β-hCG) test and transvaginal ultrasonography (TVUS) that fail to identify the presence of an intrauterine or ectopic pregnancy (EP) (Rubal and Chung, Feril Steril, 98:1078-1084, 2012). The incidence rate ranges from 8 to 31%. While the majority of PUL patients are considered low-risk pregnancies during subsequent medical follow-up, approximately 7% to 20% are later diagnosed with ectopic pregnancies (Fields and Hathaway, J Midwifery Womens Health, 62:172-179, 2017). Ectopic pregnancies pose risks such as organ rupture and severe bleeding (Diagnosis and Management of Ectopic Pregnancy, BJOG, 123:e15-e55, 2016), with abdominal pain and/or vaginal bleeding being the most common symptoms (Jeffers et al., Am J Emerg Med, 85:90-97, 2024). However, clinical observations have shown that some patients may remain asymptomatic for extended periods during the progression of an ectopic pregnancy. Given this characteristic, early diagnosis and treatment of PUL becomes particularly crucial. In recent years, no consensus has been reached regarding the management plan for PUL due to its diverse nature and variability. Therefore, this paper aims to provide a comprehensive overview of the diagnosis, expectant management, and follow-up care for PUL by focusing on more in-depth and rational approaches tailored toward different groups of PUL patients to accurately identify ectopic pregnancies at an early stage and reduce their associated morbidity and mortality.