Comparison Study of Cervical Lengths between Preterm and Term Pregnant Women among the Low-Risk Women with Normal Mid-trimester Cervical Length

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Talerngsak Netsirininkul
Chanisorn Termsarasab
Nattagorn Kongkit
Panutsaya Sennunta
Chidsanupong Techawong
Sasinapa Suanpoot



Background: Universal mid-trimester cervical length screening protocol by transvaginal ultrasonography has showed the cost-effectiveness for prevention of preterm birth. However, low-risk pregnant women with normal cervical lengths may not get the benefit from this protocol. The possible detection of the differences of cervical lengths between preterm and term pregnant women in this group could empower this universal screening protocol.

Objective: To compare the mid-trimester cervical lengths between preterm and term pregnant women among the low-risk women who had normal cervical lengths measured by a transvaginal ultrasound screening.

Materials and methods: A retrospective cohort study was conducted among 1,117 low-risk pregnant women with 18 to 24 weeks of gestational age (GA) who had cervical length ≥ 25 mm, from transvaginal ultrasonography at Lampang Hospital between September 2016 and September 2019. The delivery
outcomes were recorded. The cervical lengths were compared between the preterm and term birth groups. The logistic regression analysis was used to determine the correlation of cervical length and preterm birth.

Results: The mean cervical lengths of preterm and term pregnant women were not significantly different (40.2 ± 6.4 vs 41.6 ± 6.7 mm, p=0.052). The mean cervical length in preterm with GA less than 34 weeks was 40.9 ± 7.1 mm and that of preterm with GA 34 to 36 weeks was 40.0 ± 6.1 mm, comparable with term pregnant women (p=0.598 and p=0.047 respectively). The number of preterm births decreased when an increasing of cervical length was observed.

Conclusion: Among the low-risk women with mid-trimester cervical length ≥25 mm from the universal transvaginal ultrasound, the mean cervical length was not different between those with preterm birth and those with term birth.



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Netsirininkul, T., Termsarasab, . C., Kongkit, N., Sennunta, . P. ., Techawong, C., & Suanpoot , S. (2021). Comparison Study of Cervical Lengths between Preterm and Term Pregnant Women among the Low-Risk Women with Normal Mid-trimester Cervical Length. Lampang Medical Journal, 41(2), 49–57. Retrieved from
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