(425) Interval follow up for intermediate cervical length (26 - 29mm) identified during routine anatomy scan

Identifying patients at risk for spontaneous preterm birth (sPTB) remains a challenge because most have no history. For patients with a singleton gestation and no history of sPTB, some institutions offer universal cervical length (CL) screening via transvaginal ultrasound (TVUS). Those with a CL ≤ 25mm may receive vaginal progesterone (VP). Patients with an intermediate CL (26 – 29mm) also have increased risk for sPTB, however there are no management recommendations. This study aims to determine an appropriate TVUS follow-up (f/u) interval for patients with an intermediate CL.

Study Design:

This is a 5 year retrospective cohort of patients with a singleton gestation, no sPTB history, an intermediate CL seen during CL screening, and with ≥1 f/u TVUS at ≤ 24 6/7 weeks gestation. The primary outcome measure is incidence of short cervix.

Results:

An intermediate CL was found in 157 patients. 61 (38%) had no sPTB history and ≥1 f/u TVUS. The mean f/u interval was 18.3 ± 10.0 days, with 77 total f/u TVUS. At follow up, 19 patients (31%) were diagnosed with short cervix ≤ 25mm, with the mean time to diagnosis of 18.0 ± 8.0 days. The f/u intervals with the greatest yield was 15 – 21 days and 22 – 28 days, with 6 (30.0%) and 5 (41.7%) patients respectively diagnosed with short cervix (Figure 1). Compared to a 14 day f/u interval, significantly more patients with a short cervix were identified within 28 days [7 (36.84%) vs. 18 (94.7%), p < .001] (Figure 2). The mean delta CL was -2.4mm. Two patients progressed to a severely short cervix ( < 10mm). Of those diagnosed with short cervix, 12 (63.2%) started VP and 7 (36.8%) did not. No patients with VP delivered < 37 weeks gestation, and 1 patient without VP delivered at 36 5/7 weeks gestation.

Conclusion:

In patients with no history of sPTB and an intermediate CL, 31% will progress to short cervix and may be VP candidates. Given that 94.7% of those patients with a short cervix were identified within a 28 day f/u interval, a single f/u TVUS 3-4 weeks after the initial study will allow for identification of these patients and for appropriate intervention.