[New markers of the risk of preterm delivery]

Abstract

Preterm births account for 5.9% of all deliveries in France, a proportion that has not changed noticeably over the past 30 years. Neither risk scores nor systematic digital vaginal examinations at prenatal consultations have helped to diminish the incidence of prematurity. Because an indispensable prerequisite to reducing this incidence is better identification of the patients at risk, new approaches towards this end have been proposed in recent years. Various studies have shown that fetal fibronectin in cervico-vaginal secretions between 23 and 36 weeks' gestation can be used to identify, among patients with uterine contractions and clinically observable modifications of the cervix, a subgroup of women at very high risk of preterm delivery. Systematic assays for fetal fibronectin among low-risk women are not, however, valuable, because of both the low prevalence of preterm delivery in such a population and the poor positive predictive value. Transvaginal ultrasound of the cervix furnishes an objective and noninvasive method for ascertaining cervical status. Various studies have shown that, among patients presenting signs of preterm labor, the risk of preterm birth is higher when the cervical length, measured with ultrasound, is less than a given cut-off point (the good predictive values of which have been ascertained). Transvaginal ultrasound is also useful among the general population. Measurement of cervical length thus ought to be incorporated into the routine ultrasound performed in this population. Moreover, in addition to cervical shortening, other abnormal ultrasound findings independently associated with an increased risk of preterm delivery include the following: dilatation of the internal os, wedging, funneling (protrusion of amniotic membranes into the cervix), dynamic changes in the degree of dilation of the cervical canal (opening of the internal os or protrusion of membranes) observed, either spontaneously during contractions or after pressure on the fundus. Because fibronectin assays and cervical ultrasound allow patients at risk of true preterm labor to be identified earlier and more accurately, they should improve the chances that tocolytic treatment will succeed. They also ought to reduce the iatrogenic disorders related to prevention of preterm birth (excessive tocolysis and extended hospitalizations) without raising the incidence of such births.