How is preterm labor predicted?

Updated: May 04, 2021
  • Author: Michael G Ross, MD, MPH; Chief Editor: Carl V Smith, MD  more...
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Methods used for predicting preterm birth include home uterine activity monitoring (HUAM), assessments of salivary estriol, fetal fibronectin (FFN), the presence of BV, and cervical length assessment.

  • While hospital tocodynamometry has been effective for monitoring uterine contractions to evaluate preterm labor, HUAM has not been proven valuable in detecting or preventing preterm birth and is not currently recommended for use.

  • The proposed use of salivary estriol measurements in detecting preterm labor was based on the belief that the adrenal gland production of dehydroepiandrosterone increases before the onset of labor, which results in an increase of maternal estriol. Unfortunately, maternal estriol levels show diurnal variation, peaking at night, and are suppressed by betamethasone administration, thereby decreasing the predictive value of salivary estriol in the detection of preterm delivery risk.

  • FFN is a basement membrane protein that helps bind placental membranes to the decidua. While a negative FFN is helpful in predicting women who are not destined to deliver preterm, a positive FFN has limited value in predicting women who will deliver preterm. Nevertheless, FFN has a predictive value in identifying patients who will or will not deliver within the subsequent 1-2 weeks.

  • While the presence of BV has been associated with the risk of preterm delivery, prospective treatment trials eradicating asymptomatic BV failed to reduce the risk of preterm delivery.

  • Longer term prediction of the risk of preterm delivery is achieved by cervical length measurements. A short cervical length in the early or late second trimester has been associated with a markedly increased risk of preterm labor and delivery (see discussion on cervical length). The prediction of preterm delivery may potentially be improved by combining FFN testing with measurements of cervical length.

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