The association between second trimester CL and PTL
The literature indicates that the shorter the cervix, thegreater the chance of the patient delivering prior to term.However, the most important predictive ability of CL involves very early delivery, which is accompanied by highrates of perinatal mortality and morbidity. For example,
Romero, one of today’s real stars in
perinatal medicine, andhis group have found the same relationship as Heath
in very short cervices: a 50% rate of PTB at <32 weekswith a CL of 1.5 cm.
However, only 8% of those who deliver at that time will have a CL of 1.5 cm. Therefore, thetest is best used to adjust the relative risk of PTB in high-risk
patients, but, as a screening test,
especially in low-riskpopulations, it has questionable value. The high negative
predictive value of a long cervix (>3.5cm) at 20–24 weeksof gestation can be very reassuring, especially in those with
a history of mid-trimester or early third trimester losses.On the other hand, a short cervix does not always portend
gloom and doom for every woman who has one.
How important is funneling?
Some studies have attempted to
correlate the presence offunneling by itself with PTB. However, the strongest correlation is with CL, which has to be shorter, in any case,in the presence of funneling. Nevertheless, Rust and other
authors have found that the presence or absence of a funnelhas an independent relationship with early birth, over and
above that of a shortened CL. Althuisius has suggestedthat there are different processes leading to labor and aTYVU continuum may not fit every situation because thecervix may thin out without a wedge, and effacement inearly labor will give way to a short T-shaped cervix.
We simply have been measuring the length of the cervixand note the presence or absence of a funnel.