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Sonographic measurement of cervical length and fetal fibronectin testing in threatened preterm labor.
Tsoi E, Akmal S, Geerts L, Jeffery B, Nicolaides KH.
Ultrasound Obstet Gynecol 2006;27:368-72 pdf -
Cervicovaginal fibronectin and cervical length at 23 weeks of gestation: relative risk of early preterm delivery.
Heath VC, Daskalakis G, Zagaliki A, Carvalho M, Nicolaides KH.
BJOG 2000;107:1276-81