Bedside clinical decision tool — admit vs. discharge, progesterone/cerclage candidacy, corticosteroid timing
Romero et al. — NICHD/NIH Perinatology Research Branch
1. Romero R, Conde-Agudelo A, Da Fonseca E, et al. Vaginal progesterone for preventing preterm birth and adverse perinatal outcomes in singleton gestations with a short cervix: a meta-analysis of individual patient data. Am J Obstet Gynecol. 2018;218(2):161–180.
Defines vaginal progesterone efficacy (RR 0.62, 95% CI 0.47–0.81) for sPTB <33 wks in singletons with CL ≤25 mm. N=974 women, 5 high-quality RCTs. High-quality GRADE evidence.
2. Romero R, Conde-Agudelo A, El-Refaie W, et al. Vaginal progesterone decreases preterm birth and neonatal morbidity and mortality in women with a twin gestation and a short cervix: an updated meta-analysis of individual patient data. Ultrasound Obstet Gynecol. 2017;49(3):303–314.
Twin gestations with CL ≤25 mm: vaginal progesterone reduces PTB <33 wks (31.4% vs 43.1%; RR 0.69, 95% CI 0.51–0.93). N=303 women, 6 RCTs. Moderate-quality GRADE evidence.
3. Conde-Agudelo A, Romero R. Vaginal progesterone is as effective as cervical cerclage to prevent preterm birth in women with a singleton gestation, previous spontaneous preterm birth, and a short cervix: updated indirect comparison meta-analysis. Am J Obstet Gynecol. 2018;219(1):10–25.
In singleton + prior PTB + CL <25 mm: vaginal progesterone and cerclage equally efficacious. Choice guided by adverse events, cost, and patient preference.
4. Conde-Agudelo A, Romero R. Prediction of preterm birth in twin pregnancies with transvaginal cervical length. Am J Obstet Gynecol. 2010;203(2):128.e1–14.
Twins: CL ≤20 mm at 20–24 wks predicts PTB <32 wks (pooled sensitivity 39%, specificity 96%, LR+ 10.1). N=21 studies, 3,523 women.
Hassan et al. — NICHD/NIH Perinatology Research Branch
5. Hassan SS, Romero R, Berry SM, et al. Patients with an ultrasonographic cervical length ≤15 mm have nearly a 50% risk of early spontaneous preterm delivery. Am J Obstet Gynecol. 2000;182:1458–1467.
CL ≤15 mm associated with ~50% risk of spontaneous PTB <34 weeks. N=6,877 asymptomatic women 14–24 weeks. Established the clinical 15 mm threshold.
6. Hassan SS, Romero R, Vidyadhari D, et al. Vaginal progesterone reduces the rate of preterm birth in women with a sonographic short cervix: a multicenter, randomized, double-blind, placebo-controlled trial (PREGNANT trial). Ultrasound Obstet Gynecol. 2011;38(1):18–31.
RCT
CL 10–20 mm: vaginal progesterone gel 90 mg/day reduces PTB <33 wks by 45% (RR 0.55, 95% CI 0.33–0.92). NNT=14. N=458 singleton pregnancies.
Gudicha et al. — NICHD/NIH Perinatology Research Branch
7. Gudicha DW, Romero R, Kabiri D, et al. Personalized assessment of cervical length improves prediction of spontaneous preterm birth: a standard and a percentile calculator. Am J Obstet Gynecol. 2021;224:288.e1–17.
OR 13.4 (95% CI 8.8–20.6) for CL ≤25 mm and OR 24.3 (95% CI 12.9–45.9) for CL ≤15 mm for PTB <32 weeks. N=7,336. Provides the basis for personalized CL risk thresholds.
Iams et al. — NICHD MFMU Network
8. Iams JD, Goldenberg RL, Meis PJ, et al. The length of the cervix and the risk of spontaneous premature delivery. NICHD MFMU Network. N Engl J Med. 1996;334(9):567–572.
Landmark Cohort
Defines the continuous, exponential relationship between cervical length and sPTB risk. N=2,915 singleton pregnancies at 24 and 28 weeks. Foundational dataset for all subsequent CL research.
| Cervical Length | Percentile (24 wks) | Risk sPTB <35 wks | Source |
|---|---|---|---|
| >40 mm | >90th | ~1% | Iams et al. NEJM 1996 |
| 26–40 mm | 25th–90th | ~2–4% | Iams et al. NEJM 1996 |
| 21–25 mm | 10th–25th | ~7–18% | Iams et al. NEJM 1996 |
| 16–20 mm | 5th–10th | ~25–30% | Hassan/Romero AJOG 2000 |
| 11–15 mm | <5th | ~35–50% | Hassan/Romero AJOG 2000 |
| 1–10 mm | <1st | ~50–80% | Gudicha/Romero AJOG 2021 |
Risk estimates are from asymptomatic singleton populations without intervention. Highlighted rows represent candidacy thresholds for progesterone/cerclage per SMFM/ACOG guidance.