Today and the future
For women with a history of preterm birth, cervical length screening is now routine. For low-risk pregnant women – those without a history of previous spontaneous preterm delivery – various approaches are currently taken. Most physicians recommend assessing the cervical length transabdominally at the time of the 18-20-week ultrasound, and proceeding to transvaginal ultrasonography if the cervical length is less than 3 cm or 3.5 cm.
To reliably image the cervix with transabdominal ultrasound, it should be performed with a full bladder and with the understanding that the cervix appears longer (6 mm longer, on average) when the bladder is full (Aust. N. Z. J. Obstet. Gynaecol. 2014;54:250-55).
Transvaginal ultrasound has been widely recognized as a sensitive and reproducible method for detecting shortened cervical length. Overall, this tool has several advantages over the transabdominal approach. However, the lack of universal access to transvaginal ultrasound and to consistently reliable cervical length measurements have been valid concerns of those who oppose universal transvaginal ultrasound cervical length screening.
Such concerns likely will lessen over time as transvaginal ultrasound continues to become more pervasive. Several years ago, the Perinatal Quality Foundation set standards for measuring the cervix and launched the Cervical Length Education and Review (CLEAR) program. When sonographers and physicians obtain training and credentialing, there appears to be only a 5%-10% intraobserver variability in cervical length measurement. (The PQF’s initial focus in 2005 was the Nuchal Translucency Quality Review program.)
Increasingly, I believe, transvaginal ultrasound cervical length measurement will be utilized to identify women at high risk for early preterm birth so that low-risk women can receive progesterone and high-risk women (those with a history of preterm birth) can be considered as candidates for cerclage placement. In the process, the quality of clinical care as well as the quality of our research data will improve. Whether and when such screening will become universal, however, is still uncertain.
Dr. Werner reported that she has no financial disclosures relevant to this Master Class.