Test can aid pregnant women

An underused screening test is available to pregnant women that can help rule out the largest cause of death and disorders among newborns.

Unlike amniocentesis or cystic-fibrosis testing, this exam is designed to judge not the health of the baby but the health of the pregnancy itself. The so-called fetal fibronectin test, or fFN, measures the risk of preterm delivery, defined as birth that occurs at less than 37 weeks' gestation. About 400,000 babies each year are born prematurely, putting them at risk for death and often serious health problems.

The benefits of the test are limited because of its high rate of false positives. In studies of women with symptoms of preterm labor, about 40 percent of those with a positive fFN reading — indicating a risk for early delivery — carried their babies to term anyway. Such false positives can push a woman's anxiety level higher than if she hadn't taken the test and could lead to unnecessary medical treatment.

But the vast majority of fFN tests have come back negative, and here is where their value resides. In women who have symptoms of preterm labor — such as contractions or unusual discharge — a negative score signals a better-than-90 percent chance that delivery will not occur in the next two weeks. That may not seem like much, but it can spare a woman anxiety as well as unneeded medical treatment during that time. And some doctors repeat the test to continually update a woman's risk. In a woman without preterm-delivery symptoms, the all-clear zone lasts four weeks.

Nicole Baker, at high risk for preterm labor because of prior abdominal surgery and because she was carrying twins, was able to keep working at a Manhattan law firm through the majority of her pregnancy last year only because of three negative fFN findings. "The peace of mind that test gave me was incredible," says Baker, who delivered healthy twins in the 36th week of her pregnancy.

About two in 10 pregnant mothers either have risk factors or symptoms of preterm labor. Risk factors include multiple fetuses and a previous preterm delivery. Yet only about one in eight babies is born prematurely, often from a mother who had neither symptoms nor risk factors.

The standard measures for determining which women actually are experiencing preterm labor — contraction frequency and a digital exam — aren't that accurate. Using those measures, "we overdiagnose premature labor probably 30-40 percent of the time," says Jay Iams, professor of maternal fetal medicine at Ohio State University.