There is now ample evidence that measuring the cervix with transvaginal ultrasound can identify pregnancies that may be at risk for preterm labor and delivery and treating them with progesterone may decrease preterm labor and delivery.
"Term labor is preceded by cervical ripening and effacement by several days. It would make logical sense that preterm cervical effacement would similarly predict preterm delivery. Since the 1990s, research from various countries has shown that cervical effacement, detected as a short cervix by transvaginal ultrasound in the mid-trimester, is indeed a powerful predictor of spontaneous preterm birth. Detecting women at high risk for preterm birth without proven effective therapies or interventions, however, would only create anxiety for the mother and frustration for the physician. Routine screening, therefore, traditionally was not offered."
"Today, however, we have ample evidence from the past decade of the safety and benefit of vaginal progesterone – and possibly other interventions – in women with singleton gestation and cervical shortening. Multiple studies have demonstrated that vaginal progesterone can significantly cut the rate of spontaneous preterm birth among the approximately 2% of women who have an asymptomatic short cervix (most commonly defined as less than or equal to 2 cm) in the mid-trimester."
"In a committee opinion on "Incidentally Detected Short Cervical Length" issued in April this year, the American College of Obstetricians and Gynecologists (ACOG) recommended that a cervical length measurement be performed at the time the ultrasound examination is undertaken for fetal anatomic survey at around 18-22 weeks’ gestation and said "cervical length measured by transvaginal ultrasound examination is a useful screening test for predicting spontaneous preterm birth."
"Treatment with vaginal progesterone also was associated in singletons with significant reductions in the rate of preterm birth at less than 35 weeks’ and less than 28 weeks’ gestation, the incidence of RDS, composite neonatal morbidity and mortality, birth weight, and NICU admission."