Main Findings
Our study identified a negative association between CL measured during
the second trimester of pregnancy and the rate of sPTB. CL ≤31.7mm is an
important risk factor for PTB at ≤37 weeks and CL ≤25mm is associated
with extremely severe, severe, moderate and late PTB whereas CL of
25–30mm is associated with late PTB. This study also confirms previous
observational studies that found low BMI, previous abortion, previous
PTB, CL ≤30mm, funneling and sludge as predictors for PTB13–15.
The most relevant risk factor for PTB in a singleton pregnancy is a
previous history of PTB; however, in nulliparous women this does not
apply. We had almost half of the sPTB in nulliparous women and TVU is an
important mean to identify nulliparous women at risk of PTB. In those
women, except for BMI, the other important risk factors are directly
connected to the second trimester TVU results. Thus, considering the
higher incidence of sPTB in Brazil and globally 16,
TVU is an important tool to routinely identify these women.
As a screening test for PTB, TVU did not present good performance to
predict PTB at <37 weeks. This result agrees with previous
studies that did not find high sensitivity or acceptable specificity to
consider TVU as a screening test to predict late PTB17,18. Nevertheless, we can consider that TVU has a
moderate prognostic performance to predict sPTB at <34 weeks
and, moreover, has a good performance for predicting sPTB at
<28 weeks, with a high sensitivity and acceptable specificity.
The extremely severe and severe PTB correspond to only 5% of all
premature deliveries but are responsible for most deaths associated with
PTB 3.
There is an inverse correlation between long-term morbidity and adverse
neurodevelopmental outcomes with gestational age at birth, which incurs
higher medical costs and extrapolates this health problem to the
economic sphere, generating a huge financial impact on the health
system. The suggested NNS to identify a woman under real risk for an
early preterm birth is very acceptable for a screening test. Thus,
offering TVU as a screening test for women at risk of moderate and
extreme sPTB would increase the reaching of optimal timing for antenatal
corticosteroid administration 19 and allow preventive
treatments for reducing sPTB as progesterone, cervical pessary or
cerclage8,20.