(368) Utility of extended cervical length surveillance among asymptomatic patients with prior spontaneous preterm birth

Controversy exists regarding the benefit of extended cervical length (CL) surveillance with transvaginal ultrasound (TVUS) beyond 23 6/7 weeks among asymptomatic patients with prior spontaneous preterm birth (sPTB).  

Study Design:

This retrospective cohort study evaluated extended surveillance (ES) in asymptomatic patients with prior sPTB. Patients were included if CL surveillance began prior to 23 6/7 weeks and ≥ 2 TVUS CL measurements were performed. Patients with previable birth, multiple gestations, or major fetal anomalies were excluded. Two groups were identified: routine surveillance (RS) to 23 6/7 weeks, and ES to 32 6/7 weeks. Demographic data and pregnancy outcomes were recorded. The primary outcome was sPTB before 34 0/7 weeks. Chi squared and T-test were used for statistical analysis. A P value < 0.05 was significant.

Results:

Between 2017 and 2023, 8653 TVUS CLs were performed, and 333 patients met inclusion criteria.  Maternal characteristics were similar. By 23w6d, 273 patients (81.9 %) had a normal CL (nCL), and 60 patients (18.0 %) had a short CL (sCL) < 25 mm.  In the nCL group, 93 continued ES and 5 (5.4 %) were then diagnosed with sCL (Figure 1). There is no difference in incidence of sPTB or neonatal outcomes. The sensitivity of ES for sPTB < 34 0/7 weeks is 66%, and the positive predictive value is 40%. The number needed to detect one sCL after 23 6/7 weeks is 19 patients, and 50 patients to detect one sPTB < 34 0/7 weeks. The median time from diagnosis of sCL to delivery is 67 (interquartile range 63 - 100) days. The ES group had significantly more triage visits (mean 1.67 vs 2.11, p = 0.02).

Conclusion:

While ES in asymptomatic patients with prior sPTB may effectively identify patients who will deliver before 34 0/7 weeks gestation, there is no currently accepted intervention to prevent sPTB. Because ES does not predict birth within 7 days of diagnosis, a sCL past 23 6/7 weeks should not direct medication administration for neonatal benefit. If an effective strategy is identified for his population, then surveillance past 23w6d gestation may be a reasonable policy.