Cervical Length Percentile Explorer

Interactive reference chart for transvaginal cervical length by gestational age. Compare your patient's measurement against Romero/Gudicha 2021 and Iams 1996 normative percentile curves. Includes the SMFM/ACOG 25 mm intervention threshold.

Created by Professor Amos Grünebaum, MD · Professor of Obstetrics & Gynecology in New York · ObGyn Intelligence · LiveEvidence.com

Cervical Length by Gestational Age — Normative Percentiles

5th 10th 25th 50th 75th 90th/95th Iams (solid) Romero (dashed) 25 mm threshold

Gestational Age 24 weeks

16w20w24w28w32w36w40w

Patient Cervical Length

Clinical decision support tool — does not replace clinical judgment. Percentile curves are derived from published normative datasets and are intended for reference only. CL measurements should be performed by trained sonographers using standardized transvaginal technique per SMFM/ISUOG guidelines. Management decisions should be individualized and discussed with a qualified obstetric provider.
Source: Gudicha DW, Romero R et al. Am J Obstet Gynecol. 2021;224:288.e1-17 · Iams JD et al. N Engl J Med. 1996;334:567-72 · SMFM. Am J Obstet Gynecol. 2016;215:B2-7
© 2026 LiveEvidence.com · Amos Grünebaum, MD

Publications Used in This Tool

Gudicha DW, Romero R, Kabiri D, Hernandez-Andrade E, Pacora P, Erez O, Kusanovic JP, Jung E, Paredes C, Berry SM, Yeo L, Hassan SS, Hsu CD, Tarca AL. Personalized assessment of cervical length improves prediction of spontaneous preterm birth: a standard and a percentile calculator. Am J Obstet Gynecol. 2021;224(3):288.e1-288.e17. Romero · Percentile Curves
N=5,188 singleton term-delivery controls (NICHD/NIH Perinatology Research Branch). Provides GA-specific CL percentiles 16–40 weeks. Demonstrates that a personalized percentile-based CL standard improves prediction of spontaneous preterm birth over a fixed 25 mm cutoff.

Iams JD, Goldenberg RL, Meis PJ, Mercer BM, Moawad A, Das A, Thom E, McNellis D, Copper RL, Johnson F, Roberts JM; National Institute of Child Health and Human Development Maternal Fetal Medicine Unit Network. The length of the cervix and the risk of spontaneous premature delivery. N Engl J Med. 1996;334(9):567-572. Iams · Foundational NEJM
Landmark prospective NICHD MFMU Network study. Establishes CL as a continuous predictor of preterm birth at 24 and 28 weeks. Risk increases non-linearly below 25 mm. Forms the original normative reference for CL percentiles.

Society for Maternal-Fetal Medicine; McIntosh J, Feltovich H, Berghella V, Manuck T. The role of routine cervical length screening in selected high- and low-risk women for preterm birth prevention. Am J Obstet Gynecol. 2016;215(3):B2-B7. SMFM Guideline · 25 mm Threshold
SMFM recommends vaginal progesterone for asymptomatic singleton pregnancies with CL ≤25 mm at 16–24 weeks. Defines the standard intervention threshold shown as the red dashed line.