(1062) Prospective Study on the Duration of Cervical Ultrasound Measurement on the Prevalence of Short Cervix

To assess the impact of examination duration for midtrimester cervical length (CL) assessment on the prevalence of short cervix (CL ≤ 25 mm).

Study Design:

A prospective study on asymptomatic nulliparous women with a singleton pregnancy at 20-23 weeks. Certified sonographers performed transvaginal ultrasound examination of the cervix (AIUM guidelines). After an initial CL measurement (T-0), the sonographer observed the cervix for 3 minutes and collected the shortest measurement (T-3min). For all cases with CL ≤ 30 mm, the observation was prolonged for another 3 minutes (total of 6 minutes, T-6min) along with 200 participants with CL > 30 mm. A MFM subspecialist verified all measurements and performed his own assessment for all cases with CL ≤ 30 mm (T-MFM). We compared the proportion of CL ≤ 25mm according to the shortest CL obtained at T0, T3min and T6min. Vaginal progesterone was prescribed in case of CL ≤ 25mm and all participants were followed for spontaneous preterm birth (sPTB) < 35 weeks.

Results:

We recruited 1644 participants at a median gestational age of 23 [interquartile (IQ): 22 – 23] weeks with a median CL of 35 (IQ: 32 – 39) mm and 100 (6.1%) cases of CL ≤ 25mm. The initial measurement (T0) would have identified 35 (2.1%) cases of short cervix, compared to 69 (4.2%) at T-3min and 95 (5.8%) at T-6min (p < 0.001). An extra 5 (0.3%) cases were observed by the MFM. (p < 0.001). No (0%) short cervix were observed at T-6min in the selection of participants with CL > 30mm at T-3min. Of note, the rate of spontaneous PTB < 35 weeks was 0.8% in women with CL > 25 mm; 5.7% among women with CL ≤ 25mm at T0; 2.9% among women with CL ≤ 25mm at T-3min; 3.8% among women with CL ≤ 25 mm at T-6min, and 0/5 (0%) among those with CL ≤ 25mm according to the MFM only (p=0.01).

Conclusion:

Midtrimester cervical examination duration influences the proportion of short cervixes. For optimal diagnosis, the examination should last 3 minutes after the first measurement and 6 minutes when CL ≤ 30 mm. Extending the examination beyond these limits is not necessary.