Though few studies track how often a spontaneous pregnancy after use of assisted reproductive technology occurs, those that do suggest it is not uncommon."Most recently, a French paper published this summer in the journal Fertility and Sterility found that 17 percent of women who gave birth after IVF became pregnant again within six years — this time on their own. Among couples whose IVF failed, the rate of spontaneous pregnancy was even higher: 24 percent of the women became pregnant in the years after treatment."
"A 2008 German study found that 20 percent of couples who conceived a child by intracytoplasmic sperm injection — a form of IVF in which a single sperm is injected directly into an egg — and who subsequently tried to get pregnant naturally, succeeded. Estimates suggest that normal, healthy women have around a 20 to 25 percent chance of getting pregnant per menstrual cycle."