Greater than 50% funneling before 25 weeks is associated with approximately 80% risk of preterm delivery.
Good scanning technique is essential, as excessive pressure with the probe, or presence of a distended bladder may artificially narrow the canal. Preferrably, a transvaginal scan is recommended for accurate assesment of cervical length and measurement of funneling.
- percentage funnelling: funnel length/(functional cervical length + funnel length)
- shape of funneling: V-shaped or U-shaped. U-shaped funneling have higher risk of preterm delivery 4
- depth and width of funnel: V-shaped funnel has a depth with no width; however, U-shaped funnel has width as important parameter
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