Department of Obstetrics and Gynecology, University of Rochester, School of Medicine and Dentistry, Rochester, New York 14627, USA. Shanna_Swan@urmc.rochester.edu
Fertility has been defined in many ways-from the demographers practice of simply recording the number of children born, to the precise (but difficult to measure) monthly probability of conception. Infertility is likewise variably defined, making comparison of data across studies difficult. Furthermore, there is debate about which measures/indicators/contributors are the most useful to try to track when trying to understand fertility/infertility, fecundity/subfecundity trends.