Portable monitors that detect contractions of the uterus do not appear to be useful for identifying women likely to have a preterm delivery, according to a study by the National Institute of Child Health and Human Development (NICHD).
Although they are widely prescribed for women at risk of giving birth prematurely, the NICHD study confirms earlier findings that the monitors are not useful for predicting or preventing preterm birth. The study also confirmed that several other methods being assessed as ways to predict preterm labor were of little value.
"The study found that while women who gave birth prematurely did have slightly more contractions throughout pregnancy than did women who gave birth at term, there was no detectable pattern that would predict premature birth," said Duane Alexander, M.D., Director of the NICHD.
The study was conducted at the 11 centers participating in the NICHD Network of Maternal-Fetal Medicine Units and appears in the January 25 New England Journal of Medicine. The study was led by Jay Iams, M.D., director of the Division of Maternal-Fetal Medicine at the Ohio State University Medical Center.
The portable, or ambulatory, monitors cost up to $100 a day and may be worn for up to 10 weeks. The monitors relay information to a central monitoring office, where any potential signs of early labor can be passed on to a physician.
The researchers analyzed 34,908 hours of recordings from 306 women. When the women began the study, they were in their 22nd through 24th week of pregnancy. The authors wrote that the women who gave birth before the 35th week of pregnancy had a slightly greater frequency of contractions than did the women who gave birth after the 35th week, but this information did not allow them to predict impending premature labor. A pregnancy is considered full term at 37 weeks.
"?we could identify no threshold frequency that effectively identified women who delivered preterm infants," the study authors wrote in the New England Journal of Medicine article.
The researchers also found little value of some other techniques in predicting preterm labor, including measuring the cervix and collecting a substance known as fetal fibronectin from the cervix.
"Our data indicate that ambulatory monitoring of uterine contractions does not identify women destined to have preterm delivery," the authors wrote.
Preterm birth complicates from 8 to 10 percent of all births, said Catherine Spong, M.D., Chief of NICHD's Pregnancy and Perinatology Branch and coordinator of the Maternal-Fetal Medicine Units. Premature infants are at greater risk for life-threatening infections, for a serious lung condition known as respiratory distress syndrome, and for serious damage to the intestines (necrotizing enterocolitis). Most deaths of premature infants occur among those born before the 32nd week of pregnancy. In addition, the cost of caring for premature infants in the United States exceeds $4 billion each year.