For the current week, the overall ratings of three Life Science stocks are worse, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

This week, Thermo Fisher Scientific (NYSE:TMO) falls to a D (“sell”), worse than last week’s grade of C (“hold”). Thermo Fisher Scientific manufactures and sells products to assist in the pharmaceutical, academic, and other related research and industrial markets. For a full analysis of TMO stock, visit Portfolio Grader.

Covance (NYSE:CVD) experiences a ratings drop this week, going from last week’s C to a D. Covance is a drug development services company providing a range of early-stage and late-stage product development services to the pharmaceutical, biotechnology, and medical device industries. The stock gets F’s in Earnings Growth and Earnings Momentum. The trailing PE Ratio for the stock is 35.30. To get an in-depth look at CVD, get Portfolio Grader’s complete analysis of CVD stock.

This is a rough week for BG Medicin (NASDAQ:BGMD). The company’s rating falls to D from the previous week’s C. 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. The stock gets F’s in Equity, Cash Flow, and Sales Growth. The stock price has dropped 37.5% over the past month, worse than the 4.4% decrease the Nasdaq has seen over the same period of time. For more information, get Portfolio Grader’s complete analysis of BGMD 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.