Final answer:
The most appropriate next test would be a semen analysis for the male partner.
Step-by-step explanation:
The most appropriate next test for the 45-year-old patient who hasn't been able to conceive in 2 years and had a copper IUD 2 years ago would be a semen analysis for her partner. This test examines the quantity, shape, and movement of sperm in the semen, which can help identify any underlying fertility issues in the male partner. Since infertility can be caused by problems in both partners, it is important to assess both partners when having trouble getting pregnant. The semen analysis will provide valuable information about the possible causes of infertility.