Cervical Length Screening to Reduce Preterm Birth

I understand some of these concerns, but I do not believe they are justifiable reasons for not requiring the use of a cost-effective, beneficial screening test. Such concerns are inherent to the introduction of any new test or therapy. In the past, we have successfully implemented many advances and breakthrough findings that have involved similar concerns. Even if the degree of benefit is debated, the risk-benefit ratio balance still tips toward routine screening and the use of vaginal progesterone in women with shortened cervical length – especially because there are no significant side effects. Moreover, if the SMFM can so strongly recommend frequent transvaginal ultrasound measurements for women with prior preterm birth, then the concern regarding availability of technology may not be as significant or insurmountable as some have suggested. The infrastructure and equipment for transvaginal ultrasound already exists in most centers that perform fetal ultrasound.

Certainly, transvaginal ultrasound is preferable over transabdominal ultrasound. Although transabdominal screening would be better than no screening at all, it has been shown to have higher failure rates and lower sensitivity than the transvaginal approach.

Transvaginal ultrasound by far has been the main screening tool in studies on cervical length and the risk of preterm birth as well as studies looking at the impact of intervention. In the one major study that I could identify employing transabdominal ultrasound as the primary screening tool, the percentage of women identified with a cervical length of 15 mm or less was 0.6%, compared with 1.6%-1.7% in studies using transvaginal ultrasound as the front-line screening tool. The transvaginal approach also has been shown in numerous studies to be well accepted by patients.

Some physicians have advocated the use of CerviLenz, an instrument that measures the cervico-portio length without the use of ultrasound. In the one prospective trial of CerviLenz, the instrument diagnosed cervical length less than 3 cm with a sensitivity of 88% and a specificity of 92% (J. Reprod. Med. 2007;52:385-389). Transvaginal ultrasound was needed to confirm the findings. While CerviLenz could possibly be used in areas where transvaginal ultrasound is not available, the gold standard is transvaginal ultrasound. By screening with anything less than the gold standard, we would be providing suboptimal care.

In general, most agree that some form of cervical length screening in the midtrimester is required. The major point of debate, it seems, is whether it should be transabdominal or transvaginal ultrasound. The fact is that transabdominal scan identifies less than 50% of women with short cervix, and a majority of these women have severe cervical shortening (less than 10 mm) – a scenario where vaginal progesterone is minimally effective. Using this method will have little impact on the rate of preterm deliveries.

For optimal care of pregnant women, we have instituted universal transvaginal cervical length screening of all women with singleton gestation at the time of their anatomy scan. If cervical length is 5-20 mm, vaginal progesterone is offered; if the woman had a prior preterm delivery, the choice of cervical cerclage is also offered. If the cervical length is 21-25 mm, transvaginal ultrasound is repeated in 1-2 weeks.

This column, Master Class, appears regularly in Ob.Gyn News. Dr. Khandelwal is professor of obstetrics and gynecology at Cooper Medical School of Rowan University, Camden, N.J. She was an investigator in the NIH-collaborated study on vaginal progesterone that is mentioned in this Master Class (Ultrasound Obstet. Gynecol. 2011:38:18-31), and served as a paid consultant to Watson Pharmaceuticals Inc. in its evaluation of and FDA submission in 2011 for the Prochieve vaginal progesterone gel.