T.D.
My neighbor got pregnant on the Mirena IUD a few years ago. It didn't end good...she had a miscarriage around 5 months and had to deliver the baby. But my brother-in-laws, who are twins, were conceived with the copper IUD in place. My MIL didn't find out until she was 4 months pregnant, she just thought she had the flu!!!
Good luck and I hope everything is OK!!