At what cervical length measured on transvaginal ultrasound between 16 and 24 weeks does the risk of preterm birth rise sufficiently to warrant consideration of cervical cerclage in a woman with a previous preterm birth?
- A Less than 35 mm
- B Less than 25 mm ✓
- C Less than 30 mm
- D Less than 15 mm
Correct answer: B. Less than 25 mm
Explanation
Transvaginal sonographic cervical length screening is performed between 16 and 24 weeks. A length below 25 mm defines a short cervix and identifies women at increased risk of spontaneous preterm birth; in those with a prior preterm birth, ultrasound-indicated cerclage reduces recurrence risk. Lengths under 15 mm indicate extreme shortening with very high risk but are not the screening threshold used to trigger intervention, while 30 mm and 35 mm fall within the normal range.
Reference: Williams Obstetrics, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.