Mirena & Potential Pregnancy Symptoms: False Negative Concerns

Question
I have had mirena for about 13 months an have not had a period for 12 months. I suddenly have now developed extremely tender nipples and sore breasts with some mild AM nausea. I had a course of antibiotics in mid January (know it can lessen effectiveness of contraceptives). I am driving myself crazy knowing that these symptoms are building a string case for pregnancy but we have taken one HPT with a negative result.
What is the probability that mirena can cause a false negative? HCG is going to increase astronomically regardless of hormone birth control, correct? So if I was pregnant, shouldn't the HCG be picked up by the test? We are repeating another test in a few days but I am trying to decide if I need to persue this further and get a blood test?

Answer
Dear Hart

I do not really advice hCG level determination. Its normal range is really wide and is not conclusive. if you continued not to have a period for almost 1 year and then all of a sudden you got one, I would be more concerned about ruling out the possibility of ectopic pregnancy. Mirena contains progesterone which may sometimes slow down the movement of a fertilized ovum inside the tube leading to tubal implantation instead of the normal uterine implantation.

Therefore, I advise urgent vaginal ultrasound to rule out ectopic then manage according to the findings.

Good Luck