Contraction Monitors Don't Predict Preemies
Study confirms conventional wisdom about portable machines
WEDNESDAY, Jan. 23, 2002 (HealthDayNews) -- In what experts call a disappointing confirmation of conventional wisdom, a new study shows portable devices that monitor uterine contractions can't predict a woman's risk of premature delivery.
While women who go into labor early are likely to experience early contractions, so, too, are those who deliver at term -- effectively scuttling the costly monitor's predictive value.
The findings, while not surprising, frustrate doctors who've long sought ways to foretell premature labor. Although researchers have explored several potential indicators -- from fetal protein secretions to cervical length on ultrasound -- none has proven consistently useful.
"I think, overall, this is one of the most difficult problems that obstetricians face," says Dr. Catherine Spong, chief of the pregnancy and perinatology branch at the National Institute of Child Health and Human Development. "We don't have anything that's an all-out excellent predictor" of pre-term delivery.
Between 8 percent and 10 percent of babies in the United States are born premature. Preemies are becoming more common as couples increasingly turn to assisted reproduction technologies that raise the likelihood of multiple pregnancies.
Early babies are often severely underweight and face greater odds of infections, lung trouble and other health risks that can be serious or even fatal. Together, premature delivery and low birth weight account for some 5,000 infant deaths each year in this country.
Ultra-light infants have also been shown to suffer long-term and possibly permanent developmental deficits, and even slightly premature babies may have somewhat delayed development. A study released last week, though, says they're less likely to get into trouble as teens than their full-term counterparts.
Dr. Jay D. Iams, of Ohio State University, led the latest study, which appears in tomorrow's issue of the New England Journal of Medicine.
Iams and his colleagues followed 306 pregnant women, whose average age was about 26, starting in or around their 22nd week of gestation. Their babies were considered premature if they were born before week 35 of pregnancy, which normally lasts 37 weeks to 40 weeks.
Iams' group asked the women to monitor themselves at home using the portable devices that measure the frequency, intensity and time of day of uterine contractions. Many doctors have recommended the machines, which can cost hundreds or thousands of dollars over the course of a pregnancy, but studies haven't proven them useful.
"This really seemed like a good idea, so it has been a puzzle to everyone why monitoring at home has failed" to sort threatened pregnancies from normal ones, Iams says.
The researchers also checked the women for other potential risk factors for pre-term labor, including a fetal protein called fibronectin that is sometimes present in vaginal secretions, and physical and ultrasound exams to measure the softness, dilation and length of a mother's cervix.
Women who delivered early were more likely to record frequent contractions. However, Iams and his colleagues say these failed to predict who would give birth prematurely, and probably reflect normal variations according to duration of gestation and even time of day. Nor were positive results on the other tests especially oracular.
In order of effectiveness, says Iams, ultrasound measurement of cervical length was the most predictive test, followed by feeling the cervix (also known as the Bishop score) and fetal fibronectin. Contraction monitors brought up the rear.
"None of these four tests were particularly good at identifying women who would deliver prematurely," Iams says.
However, women without the fetal protein in their vaginal secretions and those with longer cervixes were somewhat less likely to go into premature labor. Iams says these tests should be used to reassure women having early uterine contractions.
The findings support recommendations from both the American College of Obstetricians and Gynecologists and the federal government, which don't endorse home contraction monitors. And they bolster those same guidelines that call for measuring the fetal protein and gauging cervical length -- since women with negative results on those tests seem extremely unlikely to deliver early.
Despite floundering when it comes to predicting preemies, scientists have learned a great deal about what triggers ill-timed labor. Hormone changes, inflammatory reactions, vaginal tract infections and bleeding have all been shown to increase that risk. Again, however, doctors have little clue about how to pinpoint and curtail these factors before they've caused problems.
"We need to identify the genetic risk factors for these pathways that lead to premature delivery. Then we can tailor preventive therapies" to help control them, says Dr. Charles J. Lockwood, an expert in maternal medicine at New York University, and author of an editorial accompanying the journal article.
What To Do
Many pregnant women experience normal uterine contractions. However, those who have six to eight over an hour and who have persistent contractions should see their doctor, Spong says.
So what should you do if your doctor suggests you take home a contraction monitor? Just say no, says Lockwood.
You can learn more about pregnancy from the American College of Obstetricians and Gynecologists or Childbirth.org.
Read this for information about fetal fibronectin.