[Ultrasonography of the uterine cervix in pregnancy. Curve of normality in a longitudinal and cross-sectional study].

Background: The aim of the study was to establish a normality curve of cervical length variations during pregnancy in our pregnant women population, to be compared with pathological cases (risk of preterm labor and cervical incompetence).

Design: A prospective longitudinal and cross-sectional study in women with single pregnancy and without risk factors for preterm labor was carried on.

Setting: Obstetric and Gynecology Department, University of Brescia, Italy.

Population Or Sample: One hundred and thirty-four pregnant women with single pregnancy, 112 cross-sectionally and 22 longitudinally followed, with labor at term, were selected. Sixty-eight were nulliparous, 66 pluriparous. Multiple pregnancy, previous placental and vaginal bleeding were excluded.

Methods: A transvaginal probe was used to assess uterine cervix and the patients were studied from the 12th to 41st gestational week. Statistical analysis was carried out by Student's "t"-test and Z-test.

Measures: Cervical longitudinal diameter, internal uterine os and funneling were assessed.

Results: No statistically significant differences emerged in the curves with regard to nulliparous and pluriparous patients. The cut-off between normality and pathology, from the 24th to the 32nd gestational week (2ndSD), seems to correspond to a cervical length lower than 25 mm; a significant progressive decrement of the cervical longitudinal diameter begins from the 28th gestational week.

Conclusions: These results allows the gathering of reference data about normality to compare with pathology (cervical incompetence and preterm delivery), which could be useful both for prevention and follow-up of these cases.