Final answer:
The American Cancer Society report on mammogram schedules is the least valuable resource for a nurse employing evidence-based practice related to prenatal care and pregnancy; it does not directly pertain to Healthy People 2020 goals for pregnant women like the other listed resources do.
Step-by-step explanation:
The resource that would be of least value to a nurse hoping to employ evidence-based practice (EBP) in support of the Healthy People 2020 objectives for pregnant women is the report from the American Cancer Society regarding changes in the recommended schedule for mammograms. This resource does not directly relate to pregnancy and prenatal care, which is the focus of EBP for pregnant women. The other resources listed — a research study on exercise during pregnancy, a report on gestational diabetes, and a document on the benefits of vaccines during pregnancy — all provide relevant information directly related to the health and care of pregnant women and can directly inform practice in line with Healthy People 2020 goals