Introduction

An ectopic pregnancy is a life-threatening obstetric emergency in which a fertilized egg implants and begins to develop outside the uterine cavity, most commonly within the fallopian tube. Undetected or untreated, an ectopic pregnancy can lead to tubal rupture, catastrophic intra-abdominal hemorrhage, and maternal death. Medical management using the chemotherapeutic agent methotrexate has become an established and highly effective non-surgical treatment option for carefully selected patients with ectopic pregnancy, offering the prospect of resolving the condition without the risks of general anesthesia, surgical intervention, or the potential loss of the fallopian tube. Real-time imaging guidance plays an indispensable role throughout the diagnosis, treatment planning, and follow-up monitoring of patients managed medically for ectopic pregnancy, making this a clinically important area of practice for the interventional radiology and gynecology teams.

Understanding Ectopic Pregnancy

Under normal circumstances, fertilization of an egg by a sperm occurs within the fallopian tube, and the resulting embryo travels along the tube into the uterine cavity where it implants in the endometrium and develops into a pregnancy. An ectopic pregnancy occurs when this process is disrupted and the fertilized egg implants at an abnormal site outside the uterus. The fallopian tube accounts for approximately ninety-five percent of all ectopic pregnancies, with the ampullary portion of the tube being the most frequent site of implantation. Less common sites include the ovary, cervix, cesarean section scar, and the abdominal cavity. Risk factors for ectopic pregnancy include previous pelvic inflammatory disease, prior ectopic pregnancy, previous tubal surgery, endometriosis, assisted reproductive techniques, and intrauterine contraceptive device use. As the ectopic pregnancy grows, the fallopian tube is unable to accommodate it and rupture eventually occurs, causing sudden severe abdominal pain and internal bleeding that constitutes a surgical emergency.

Diagnosis and the Role of Imaging

Early and accurate diagnosis of ectopic pregnancy is critical for enabling medical management, as this option is only available before rupture occurs. The diagnosis is established through a combination of clinical assessment, serum beta human chorionic gonadotropin measurement, and transvaginal ultrasound examination. Transvaginal ultrasound is the imaging modality of choice for the evaluation of suspected ectopic pregnancy, providing high-resolution real-time visualization of the uterus, endometrial cavity, fallopian tubes, ovaries, and pelvis. Key ultrasound findings in ectopic pregnancy include an empty uterine cavity with no intrauterine gestational sac, a thickened echogenic endometrium, and an adnexal mass separate from the ovary representing the ectopic gestational sac. A live ectopic pregnancy with visible fetal cardiac activity may be identified in some cases. Free fluid in the pelvis or abdomen suggests tubal bleeding and raises concern for impending or actual rupture. The combination of a discriminatory serum beta human chorionic gonadotropin level above a defined threshold with the absence of an intrauterine pregnancy on transvaginal ultrasound is sufficient to diagnose ectopic pregnancy in the appropriate clinical context, even if the ectopic sac itself is not directly visualized.

Indications for Medical Management

Medical management with methotrexate is indicated in hemodynamically stable patients with a confirmed or strongly suspected ectopic pregnancy who meet specific clinical and biochemical criteria. Suitable candidates are those with a small unruptured ectopic pregnancy, typically with a gestational sac measuring less than three and a half centimeters, no visible fetal cardiac activity on imaging, a serum beta human chorionic gonadotropin level below a defined threshold, and no evidence of intra-abdominal bleeding or hemodynamic compromise. Additional criteria include normal renal, hepatic, and hematological function, no contraindications to methotrexate including active peptic ulcer disease, immunodeficiency, or significant hepatic or renal impairment, patient reliability for close follow-up monitoring, and the patient’s informed agreement to undergo medical rather than surgical treatment.

How Methotrexate Works

Methotrexate is a folic acid antagonist that works by inhibiting the enzyme dihydrofolate reductase, which is essential for DNA synthesis and cell division. It selectively targets rapidly dividing cells, including the trophoblastic cells of the ectopic pregnancy. By blocking trophoblast proliferation, methotrexate causes the ectopic pregnancy to cease growing , allowing the fallopian tube to recover without rupture. The drug can be administered as a single intramuscular injection, a two-dose regimen, or a multi-dose protocol depending on the clinical situation and the treating institution’s protocol. The single-dose regimen, calculated based on body surface area, is the most widely used approach and is associated with fewer side effects than multi-dose protocols while maintaining satisfactory success rates in appropriately selected patients.

Pre-Treatment Assessment and Preparation

Before administering methotrexate, a comprehensive assessment is performed to confirm patient suitability and establish baseline values for monitoring. This includes a detailed clinical history and examination, confirmation of the ectopic pregnancy diagnosis on transvaginal ultrasound, measurement of serum beta human chorionic gonadotropin, and laboratory tests including full blood count, renal function, liver function, and blood group with rhesus status. Rhesus-negative patients receive anti-D immunoglobulin prophylaxis. Patients are counselled extensively about the treatment process, the importance of strict compliance with follow-up appointments, the symptoms that should prompt emergency re-attendance, and the need to avoid folic acid supplements, alcohol, non-steroidal anti-inflammatory drugs, and sexual intercourse during the treatment period. Written informed consent is obtained before proceeding.

Monitoring and Follow-Up

Close monitoring following methotrexate administration is essential to confirm treatment success and detect early signs of failure or complications. Serum beta human chorionic gonadotropin levels are measured on days four and seven after treatment. A fall of fifteen percent or more between day four and day seven values is considered a satisfactory response and indicates that the ectopic pregnancy is resolving. If an adequate fall is not achieved, a second dose of methotrexate may be administered. Serial beta human chorionic gonadotropin measurements continue on a weekly basis until the level falls to undetectable. Transvaginal ultrasound is repeated during follow-up to monitor the adnexal mass and detect any free fluid suggesting tubal bleeding. Patients are advised that the adnexal mass may temporarily increase in size during the early treatment period due to internal bleeding within the ectopic sac, which should not be interpreted as treatment failure in the absence of hemodynamic compromise.

Risks, Side Effects, and Surgical Conversion

Medical management with methotrexate is associated with a small but recognized risk of treatment failure requiring surgical intervention, which occurs in approximately fifteen to twenty percent of patients treated with the single-dose protocol. Surgical conversion is required urgently in the event of tubal rupture, hemodynamic instability, or failure of beta human chorionic gonadotropin levels to decline appropriately despite repeat dosing. Side effects of methotrexate include nausea, vomiting, abdominal discomfort, stomatitis, and transient elevation of liver enzymes. Bone marrow suppression is rare at the doses used for ectopic pregnancy treatment. Patients must be clearly informed that any sudden severe abdominal pain, dizziness, or shoulder tip pain during the follow-up period must be treated as a potential tubal rupture and requires immediate emergency assessment.

Conclusion

Medical management of ectopic pregnancy with methotrexate, guided by precise imaging diagnosis and serial ultrasound monitoring, represents a safe, effective, and fertility-preserving alternative to surgery in carefully selected patients. The central role of transvaginal ultrasound in establishing the diagnosis, determining treatment suitability, and monitoring the response to therapy underscores the critical importance of imaging expertise throughout the management of this condition. When the correct patient is identified early and managed with appropriate medical therapy and rigorous follow-up, the fallopian tube can often be preserved, maternal morbidity is minimized, and future reproductive potential is protected.