Safety of methotrexate administration in women with pregnancy of unknown location at high risk of ectopic pregnancy

ObjectivesTo evaluate the safety of current guidelines on methotrexate (MTX) administration in women with pregnancy of unknown location (PUL) who are considered to have a high risk of underlying ectopic pregnancy (EP), and to investigate whether implementation of these guidelines would result in inadvertent exposure to MTX of viable intrauterine pregnancies (IUP).MethodsThis was a retrospective observational study of consecutive clinically stable women who were classified with PUL at the early pregnancy unit of Nepean Hospital, Sydney, Australia, between 2007 and 2021. PUL was defined as a positive pregnancy test in the absence of signs of IUP or EP on transvaginal ultrasound. Patients with a PUL that behaved biochemically like an EP, but for which the location of pregnancy was not confirmed on ultrasound, were eligible for MTX to minimize the risk of subsequent tubal rupture. Criteria discussed in the guidelines of the American College of Obstetricians and Gynecologists (ACOG), American Society for Reproductive Medicine (ASRM), Royal College of Obstetricians and Gynaecologists (RCOG) and National Institute for Health and Care Excellence (NICE) were applied to the PUL database. The number of patients eligible to receive MTX and the number with an underlying viable IUP who would be inadvertently prescribed MTX were calculated.ResultsA total of 816 women with PUL were reviewed, of whom 724 had complete data and were included in the final analysis. Six patients had persistent PUL and the remaining 718 had a diagnosis of viable IUP, non-viable IUP, EP or failed PUL. According to the ACOG, ASRM, RCOG and NICE guidelines, the rate of MTX administration among patients with PUL would have been 2.76%, 4.56%, 0.41% and 35.36%, respectively. However, no persistent PUL would have received MTX according to the ACOG, ASRM and RCOG protocols (the NICE protocol identified patients with persistent PUL with a sensitivity of 100%), and the majority of MTX treatments were unnecessary because those patients were later classified as having non-viable IUP or failed PUL. Application of ACOG and ASRM guidance could result theoretically in inadvertent MTX administration to women with an underlying viable IUP at a rate of 4.1/1000 (3/724).ConclusionsCurrent guidelines used to predict high risk of EP in the PUL population lead to inadvertent MTX administration to women with an underlying viable IUP. These guidelines should be used wisely to ensure that no wanted pregnancy is exposed to MTX. Women with PUL should be monitored carefully, and MTX should be used judiciously when the location of pregnancy is yet to be confirmed. (c) 2024 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.