Anyone who has gone through in vitro fertilization (IVF), knows that the most painful part--aside from the bill--is not knowing whether it will work. If you only knew if you'd get a baby at the end of this emotionally trying ordeal, the journey would be so much easier. Now, a group of scientists say they have a formula that can predict your odds of success.

It doesn't help your chances of having a baby. But this mathematical equation may help you decide whether you want to make this huge investment of time and money. For the most part, doctors just consider your age-which is a huge consideration. The chances of getting pregnant during any given cycle is about 24 percent but the odds plummet by your mid 30s. At 35, the chance of getting pregnant on any given cycle is 15 percent; it slips to 20 percent by age 40 and a mere 2 percent by age 42. Still, age alone does not always predict what's going to happen. We've all heard stories of 30-something women who gave up after several failed attempts and the 45-year-old with healthy twins.

The new formula, developed by Stanford University's Mylene Yao included about 50 variables, such as sperm count, prior pregnancies, and endometrial thickness. Some of the information could be gleaned before IVF, other information had to be collected after the first round. In the August 3 issue of The Proceedings of the National Academy of Sciences, Yao claimed that the formula was 1000 times better at predicting success than using age alone. "When used alone," the researchers wrote, "age may be misleading as a prognostic factor due to the complex and yet uncharacterized relationships among age, hormonal response, and embryo parameters such as blastocyst formation rate and total number of embryos."