California researchers say they have identified a method that can predict with 70 percent accuracy if in vitro fertilization will make a woman pregnant.

Study leader Dr. Mylene Yao of Stanford University School of Medicine said in typical IVF cycle produces five to 12 embryos, and doctors aim to transfer the "best quality" one or two into a woman's uterus. Nationwide, the percentage of IVF cycles that result in pregnancy for women using their own eggs ranges from about 18 percent to 45 percent, depending on age and other factors.

Yao and colleagues analyzed clinical data from 665 IVF cycles performed at Stanford in 2005. They looked at 30 variables and examined the association of each variable with IVF outcomes.

The study, published in the journal PLoS One, found that four factors were most important in determining a woman's chance of becoming pregnant: total number of embryos, number of eight-cell embryos, percentage of embryos that stopped dividing and would die and the woman's follicle-stimulating hormone level, a measurement that estimates ovarian function.

The four factors together were 70 percent accurate in predicting whether the current IVF cycle would result in a pregnancy, the study said.