Just four factors can predict with 70 percent accuracy whether a woman will become pregnant through “test-tube” baby technology known as in vitro fertilization, U.S. researchers said on Tuesday.

In vitro fertilization, or IVF, is a costly treatment that aims to increase a woman’s chances of becoming pregnant but in the United States it is successful only 18 to 45 percent of the time, according to the Society for Assisted Reproductive Technology.

Dr. Mylene Yao of Stanford University in California said she hoped that with more testing the method might be useful to couples undergoing the expensive treatment.

“People make decisions based on probability,” Yao said in a statement. “At that point, it’s really important to give a more accurate prediction.”

IVF involves surgically removing eggs from a woman’s ovaries and combining them with sperm in the lab. Doctors then pick the best embryos - typically one or two - and implant them in a woman’s uterus.

Yao’s team wanted to find out what factors most influenced the chances of a woman becoming pregnant using this method.

They analyzed data from 665 IVF cycles performed at Stanford in 2005, looking at 30 variables including patient characteristics, diagnoses, treatment methods, and characteristics of the embryo.

Reporting in the Public Library of Science journal PLoS One, they said they matched these up with women who had become pregnant.

Yao’s team was able to isolate four basic characteristics that were most likely to lead to a positive pregnancy test - the total number of embryos, the number of eight-cell embryos, the percentage of embryos that stopped dividing and would die, and the woman’s follicle-stimulating hormone level, a measure of how well a woman’s ovaries are working.

“Most remarkably, these factors describe the entire group of embryos and were more informative than characteristics of the embryos that were actually transferred back to the patients,” Yao said in an e-mail.

Typically, doctors evaluate each embryo to assess its viability, but Yao said the findings suggest certain characteristics of the group might be a stronger predictor of pregnancy.

The researchers are conducting a larger study to see if these same factors influence whether a woman successfully carries a baby to term.

“We hope that findings from our larger study that is currently in progress will have a real, clinical impact,” Yao said.

IVF can cost $10,000 or more per cycle in the United States and Yao hopes the findings will allow couples to make better choices.

Some 60 million to 80 million couples are infertile worldwide, according to the World Health Organization.

By Julie Steenhuysen
CHICAGO (Reuters)