Final answer:
The exact percentage of US mothers diagnosed with Postpartum Depression during the first year cannot be provided without referencing the specific Landmark Study of 10,000 US Mothers, but general rates in certain populations range from about 11.4% to 20.45%.
Step-by-step explanation:
The Landmark Study of 10,000 US Mothers does not provide a direct percentage of US mothers diagnosed with Postpartum Depression (PPD) during the first year, as the question suggests. For a precise percentage, one would need to reference the specific study. However, general statistics about PPD can be found in various research publications. For instance, some studies indicate that rates of postpartum depression can range from about 11.4% to 20.45% in certain populations. It is also noted that the South Carolina Department of Mental Health states that for every 200 U.S. women, an average of one woman suffers from postpartum depression. If we were to estimate based on these numbers, in a sample of 600 U.S. women, approximately three could be expected to suffer from PPD. However, without direct data from the mentioned landmark study, an accurate percentage of PPD diagnosis within the first year postpartum for US mothers cannot be provided.