Hi Customer (name blocked for privacy)-
Interestingly, the IUD doesn't produce (or add) any hormones in your body. As such, it is not likely that the tests are showing a negative reading because of the IUD. However, it is possible that you simply don't have enough pregnancy hormone in your urine yet to have a postive reading on a home pregnancy test - typically it takes a few weeks after your missed period to show positive. However, because it sounds like this is your second missed period, you should by now have enough of the hormone to have a positive test (assuming you became pregnant two cycles ago).
There are other reasons why a woman can miss her period, including stress and a hormone imbalance. You should definitely make an appointment with your doctor to get things checked out. He/she will also do a blood pregnancy test if needed, which is extremely reliable.
If you have further questions, feel free to ask!
Sincerely,
Emily
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