A new diagnostic test
offered earlier in pregnancy could help doctors determine if mothers-to-be are at risk of giving birth prematurely. The study was published in Obstetrics and Gynecology.
In addition to prior medical history exams, doctors mainly rely on two standard practices when determining if a woman is at risk for premature delivery. This includes assessing for cervical length, as shorter than normal cervix lengths are widely associated with increased risk for preterm labor. A second factor that doctors rely on is the measurement of a biomarker known as fetal fibronectin.
Fetal fibronectin is a protein produced by fetal cells, and functions as the “biological glue” that holds the fetal sac to the uterine lining. Doctors have found an association between high levels of fetal fibronectin and preterm labor. Traditional methods to assess this involve screening the woman at 22-27 weeks of gestation. And if her fibronectin levels are above 50 ng/mL, the mother-to-be is considered at high risk. This test has been more useful as a negative predictor, as women who do have high levels of fibronectin may or may not give birth very soon.
To improve on the quantitative value of fibronectin screening tests, researchers at King's College London subdivided the threshold to 10 or greater, 50 or greater, and 200 ng/mL or greater. Furthermore, they asked if measurements made earlier in the pregnancy could provide the same or better predictive value for preterm labor. For this, they compared the fibronectin amounts in women at 18 -21 weeks of gestation to those at 22-27 weeks of gestation.
Of a total of 898 women, they found that only 3.8% of women with concentrations less than 10 ng/mL delivered before 34 weeks of gestation. This rate is reassuring as it is similar to the rate of preterm deliveries for normal pregnancies (3.3%). In addition, for women whose fibronectin measurement was less than 10 ng/mL, the proportion of early delivery was similar for those measured early at 18 weeks, and those measured at 22 weeks.
In all other comparisons, the authors noted that the fibronectin measurements offer similar predictive values in both early and standard screens. This means that doctors could potentially perform the fibronectin test by as early as 18 weeks of gestation and tailor early interventions for at-risk women.
The authors also defined new thresholds for classifying risks with fibronectin levels. They offer that thresholds less than 10 ng/mL to be considered “low risk,” while those greater than 200 ng/mL to be considered higher risk.
Using the fibronectin biomarker test in conjunction with the cervical length test further improved the accuracy of diagnosing preterm labor. While more research needs to be done to hone in on specificity as well as sensitivity of the test, the study offers another way to identify those women in most need of interventions at earlier time points. This could significantly improve the prospects of safe labor and delivery for at-risk women.
Additional source: EurekAlert