Disentangling causal paths between obesity and in vitro fertilization outcomes: an intractable problem?

Research questions should be appropriate for the available data. Disentangling causal paths between obesity and in vitro fertilization outcomes may be an intractable problem, but other research questions of clinical importance can be addressed through appropriate study designs and analytic methods. (Fertil Steril (R) 2008;89:1604-5. (c) 2008 by American Society for Reproductive Medicine.).