What is the primary method to diagnose a ruptured ectopic pregnancy?

The primary method for diagnosing a ruptured ectopic pregnancy involves a combination of serial quantifiable beta-human chorionic gonadotropin (B-hCG) levels and transvaginal ultrasound. This approach is favored because it allows for the assessment of the pregnancy's viability and location.

In an ectopic pregnancy, the levels of B-hCG will typically be lower than expected for an intrauterine pregnancy based on gestational age. As the values are measured over time, a lack of appropriate rise, or a decrease, can help indicate a problem. Concurrently, transvaginal ultrasound provides imaging that helps visualize whether the embryo is located outside the uterus and can also identify associated findings such as free fluid in cases of rupture.

This diagnostic strategy is safe, non-invasive, and very effective in the early detection of ectopic pregnancies, making it the standard of care in emergency settings. Other imaging modalities such as a CT scan or MRI are not routinely used due to factors like exposure to radiation and the cost involved. Hysterosalpingography, which can assess the patency of the fallopian tubes, is also not appropriate as it primarily evaluates the uterine cavity and would not directly identify an ectopic implantation.