III. Protocol

  1. No Ultrasound pressure on Cervix, observe 5 minutes
  2. Take 3 measurements and length is the shortest of 3

IV. Exam: Normal course of Cervical Length

  1. Wide variation in Cervical Lengths at 22-30 weeks
    1. Length of 2.0 cm: 5th percentile
    2. Length of 2.5 cm: 10th percentile
    3. Length of 3.5 cm: 50th percentile
    4. Length of 4.5 cm: 90th percentile
  2. Cervical Lengths shorten with Gestational age
    1. Gestational age 16-20 weeks: 4.0 - 4.5 cm
    2. Gestational age 24-28 weeks: 3.5 - 4.0 cm
    3. Gestational age 32-36 weeks: 3.0 - 3.5 cm

V. Interpretation: Short length associated preterm birth

  1. First trimester length does not predict preterm birth
  2. Length <1 cm: Mean birth Gestational age 32 weeks
  3. Length <1.5 cm: Mean birth Gestational age 33 weeks
  4. Length <2 cm: Mean birth Gestational age 34 weeks
  5. Length <2.5 cm: Mean birth Gestational age 36.5
  6. Hassan (2000) Am J Ob Gyn [PubMed] (or open in [QxMD Read])

VI. Efficacy: Transvaginal Ultrasound in Preterm Labor

  1. Assumes signs and symptoms suggestive of Preterm Labor
  2. Cervical Length 18-30 mm
    1. Test Sensitivity: 68-100% for preterm birth
    2. Test Specificity: 44-79% for preterm birth
  3. Cervical Length <25 mm with Fetal Fibronectin >50 ng/ml
    1. High risk of preterm birth if PTL at 24-28 weeks
    2. Mozurkewich (2000) Am J Obstet Gynecol 182(6):1589-98 [PubMed] (or open in [QxMD Read])
  4. Cervical Dilation
    1. Criteria suggestive of cervical dilation
      1. U or V shape of internal os
      2. Funnel width >5 mm
      3. Funnel length (lateral border) >3 mm
    2. Test Sensitivity: 70-100% for preterm birth
    3. Test Specificity: 54-75% for preterm birth
  5. References
    1. Leitich (1999) Am J Obstet Gynecol 181(6):1465-72 [PubMed] (or open in [QxMD Read])
    2. Mozurkewich (2000) Am J Obstet Gynecol 182(6):1589-98 [PubMed] (or open in [QxMD Read])

Images: Related links to external sites (from Google)