Threatened preterm labor

The majority of women (about 90%) presenting to the labor ward with painful and regular uterine contractions at 24–36 weeks of gestation are not in true labor and do not deliver within the subsequent 7 days.

Hospitalisation and the administration of tocolytics and steroids should be reserved for women that are truly in labor and such women can be identified by sonographic measurement of cervical length and / or a positive fetal fibronectin test in cervicovaginal secretions at presentation.

In women with threatened preterm labor the rate of delivery within the subsequent 7 days is inversely related to cervical length at presentation. The cervical length is <20 mm in about 20% of women with threatened preterm labor and this group contains 75% of those that deliver within 7 days. In patients with cervical length >20 mm the risk of birth within 7 days is about 3%.

The fetal fibronectin test is positive in about 20% of women with threatened preterm labor and this group contains 75% of those that deliver within 7 days. In patients with fetal fibronectin test negative the risk of birth within 7 days is about 3%.

A combination of cervical length and fetal fibronectin could potentially reduce the screen positive rate to about 5% (rather than 20% with each test alone) and also reduce the risk of birth within 7 days in those with a negative combined test to about 1%.

1. Fuchs I, Tsoi E, Henrich W, Dudenhausen JW, Nicolaides KH. Sonographic measurement of cervical length in twin pregnancies in threatened preterm labor. Ultrasound Obstet Gynecol 2004;23:42-5.
2. Tsoi E, Fuchs IB, Rane S, Geerts L, Nicolaides KH. Sonographic measurement of cervical length in threatened preterm labor in singleton pregnancies with intact membranes. Ultrasound Obstet Gynecol 2005;25:353-6.
3. Sotiriadis A, Papatheodorou S, Kavvadias A, Makrydimas G. Transvaginal cervical length measurement for prediction of preterm birth in women with threatened preterm labor: a meta-analysis. Ultrasound Obstet Gynecol 2010;35:54-64.
4. Boots AB, Sanchez-Ramos L, Bowers DM, Kaunitz AM, Zamora J, Schlattmann P. The short-term prediction of preterm birth: a systematic review and diagnostic metaanalysis. Am J Obstet Gynecol 2014;210:54.e1-54.e10.