This week, the ratings of three Life Science stocks on Portfolio Grader are down. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

This week, BG Medicin (NASDAQ:BGMD) falls to a D (“sell”), worse than last week’s grade of C (“hold”). BG Medicine is a life sciences company focused on the discovery, development and commercialization of novel diagnostic tests based on biomarkers for high-value market opportunities in healthcare that it identifies. In Portfolio Grader’s specific subcategories of Equity, Cash Flow, and Sales Growth, BGMD also gets an F. The stock price has dropped 17.2% over the past month, worse than the 3.6% increase the Nasdaq has seen over the same period of time. To get an in-depth look at BGMD, get Portfolio Grader’s complete analysis of BGMD stock.

ShangPharma (NYSE:SHP) earns a D this week, falling from last week’s grade of C. ShangPharma is a pharmaceutical and biotechnology research and development, or R&D, outsourcing company. The stock gets F’s in Earnings Surprise and Margin Growth. The stock currently has a trailing PE Ratio of 37.30. For a full analysis of SHP stock, visit Portfolio Grader.

This week, Sequenom Inc. (NASDAQ:SQNM) drops from C to a D rating. Sequenom is a molecular diagnostic testing and genetics analysis company. The stock gets F’s in Equity and Cash Flow. Share prices fell 5.4% over the past month. As of Jan. 17, 2013, 30.3% of outstanding Sequenom Inc. shares were held short. For more information, get Portfolio Grader’s complete analysis of SQNM stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.