Obstetrics Book

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Ultrasound Exam of Cervical LengthAka: Uterine Cervix Assessment by Ultrasound, Preterm Labor Assessment with Ultrasound, Cervical Length

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  1. See Also
    1. Preterm Labor
    2. Preterm Labor Management
    3. 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. 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) :
  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
    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
      2. Mozurkewich (2000) Am J Obstet Gynecol 182(6):1589
  7. References
    1. Doyle (2004) Obstet Gynecol Clin North Am 31:125

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