II. Indications
III. Protocol
- No Ultrasound pressure on Cervix, observe 5 minutes
- Take 3 measurements and length is the shortest of 3
IV. Exam: Normal course of Cervical Length
- Wide variation in Cervical Lengths at 22-30 weeks
- Length of 2.0 cm: 5th percentile
- Length of 2.5 cm: 10th percentile
- Length of 3.5 cm: 50th percentile
- Length of 4.5 cm: 90th percentile
- Cervical Lengths shorten with Gestational age
- Gestational age 16-20 weeks: 4.0 - 4.5 cm
- Gestational age 24-28 weeks: 3.5 - 4.0 cm
- Gestational age 32-36 weeks: 3.0 - 3.5 cm
V. Interpretation: Short length associated preterm birth
- First trimester length does not predict preterm birth
- Length <1 cm: Mean birth Gestational age 32 weeks
- Length <1.5 cm: Mean birth Gestational age 33 weeks
- Length <2 cm: Mean birth Gestational age 34 weeks
- Length <2.5 cm: Mean birth Gestational age 36.5
- Hassan (2000) Am J Ob Gyn [PubMed]
VI. Efficacy: Transvaginal Ultrasound in Preterm Labor
- Assumes signs and symptoms suggestive of Preterm Labor
- Cervical Length 18-30 mm
- Test Sensitivity: 68-100% for preterm birth
- Test Specificity: 44-79% for preterm birth
- Cervical Length <25 mm with Fetal Fibronectin >50 ng/ml
- High risk of preterm birth if PTL at 24-28 weeks
- Mozurkewich (2000) Am J Obstet Gynecol 182(6):1589-98 [PubMed]
- Cervical Dilation
- Criteria suggestive of cervical dilation
- U or V shape of internal os
- Funnel width >5 mm
- Funnel length (lateral border) >3 mm
- Test Sensitivity: 70-100% for preterm birth
- Test Specificity: 54-75% for preterm birth
- Criteria suggestive of cervical dilation
- References