Second-trimester cervical ultrasound: associations with increased risk for recurrent early spontaneous delivery.

OBJECTIVE: To determine whether short cervical length or internal os funneling before 20 weeks' gestation predicts early preterm birth or pregnancy loss in women with at least one prior spontaneous early preterm birth.
METHODS: Transvaginal cervical ultrasound examinations were done every 2 weeks on 69 women with singleton gestations and histories of at least one prior spontaneous birth between 16 and 30 weeks' gestation. The results of those examinations were correlated with gestational age at delivery.
RESULTS: Among 53 women who had ultrasound examinations before 20 weeks' gestation, those with cervical lengths at or below the tenth percentile for the study population (22 mm, n = 4) or funneling of the internal os (n = 5) were more likely than women without those factors to have spontaneous preterm births within 2 weeks (33% versus 0%, P = .01) or 4 weeks from the ultrasound examination (67% versus 0%, P < .001) or before 35 weeks' gestation (100% versus 19%, P < .001). Short cervical length or funneling between 20-24 and 25-29 weeks was also associated with increased risk of spontaneous preterm birth before 35 weeks' gestation (P < or = .05 and P = .002, respectively) but not with increased risk of spontaneous preterm birth within 2 or 4 weeks of ultrasound examination.
CONCLUSION: Women with prior early spontaneous preterm births who have short cervical lengths or funneling of the internal cervical os before 20 weeks' gestation are at increased risk of subsequent spontaneous preterm birth.