Obstetrics Book

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Ultrasound Exam of Cervical Length

Aka: Ultrasound Exam of Cervical Length, Uterine Cervix Assessment by Ultrasound, Preterm Labor Assessment with Ultrasound, Cervical Length
  1. See Also
    1. Obstetric Ultrasound
    2. Preterm Labor
    3. Preterm Labor Management
    4. Fetal Fibronectin
  2. Indications
    1. Preterm Labor
  3. Protocol
    1. No Ultrasound pressure on Cervix, observe 5 minutes
    2. Take 3 measurements and length is the shortest of 3
  4. 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
  5. 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]
  6. 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]
    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]
      2. Mozurkewich (2000) Am J Obstet Gynecol 182(6):1589-98 [PubMed]
  7. References
    1. Doyle (2004) Obstet Gynecol Clin North Am 31:125 [PubMed]

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