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, 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) gets weaker ratings this week as last week’s C drops 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 35.4.

To get an in-depth look at CVD, get Portfolio Grader’s complete analysis of CVD stock.

The rating of BG Medicin (NASDAQ:BGMD) slips from a C to a D. 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 30.6% over the past month, worse than the 5% increase the Nasdaq has seen over the same period of time. For a full analysis of BGMD stock, visit Portfolio Grader.

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.