1. Treatment of patients with long-standing unexplained subfertility with in vitro fertilization 
Peter F Donderwinkel, M.D., Hester van der Vaart, Victorien M Wolters, Arnold H Simons, M.D., Gerard Kroon, Maas-Jan Heineman, M.D., Ph.D. 
Fertility and Sterility 
Volume 73, Issue 2, Pages (February 2000)
DOI: /S (99)00518-X

2. Figure 1
Life-table analyses of pregnancy risk. Group 1 = couples awaiting IVF treatment. Spontaneous pregnancy is the terminal event. Couples not becoming pregnant are considered censored on the day of withdrawal or on the day of the first IVF treatment. Group 2 = couples awaiting and receiving IVF treatment. Spontaneous pregnancy and IVF pregnancy are terminal events. Couples not becoming pregnant are considered censored on the day of withdrawal.
Donderwinkel. Unexplained subfertility. Fertil Steril 2000.
Fertility and Sterility  , DOI: ( /S (99)00518-X)