Pros and cons of maternal cervical length screening to identify women at risk of spontaneous preterm delivery.

Large randomized controlled trials have demonstrated that universal maternal cervical length screening and treatment with daily vaginal progesterone in women with short cervical length reduces the risk of preterm birth, but large numbers of women must be screened to prevent a relatively small number of preterm deliveries. Issues that should be considered while implementing universal cervical length screening include: (1) the standards of quality and reproducibility for transvaginal ultrasound cervical length ascertainment; and (2) the implications of screening on the application of therapeutic strategies to populations not known to benefit (so-called "indication creep"). Optimal strategies to employ cervical ultrasound and progesterone treatment might be revealed by additional studies investigating cervical length cutoffs, frequency of screening, selective screening in higher-risk groups, and the use of transabdominal cervical length screening as a surrogate for transvaginal cervical length screening.