Transvaginal sonographic cervical length changes during normal pregnancy

Objective. To examine the relationship between cervical length and gestational age in normal pregnancy in nulliparous versus parous women. Methods. We studied a cross-sectional sample of 321 pregnant women, including 185 nulliparous and 136 multiparous women. The inclusion criteria were sonographic confirmation of gestational age within the 12th week, the absence of any risk factors for preterm birth, and uncomplicated pregnancy with expected delivery during the 38th to 42nd weeks. Cervical length was measured in a straight line if the cervix did not show any curvature; in the presence of cervical curvature, the measurement was broken down into 2 or more segments. Results. There was a relationship between gestational age and cervical length, which could be described with a linear function (R = 0.92; R-2 = 0.85; P < .001). Moreover, there was no statistically significant difference between multiparous and nulliparous women. Conclusions. Our study shows that cervical length is comparable in nulliparous and multiparous women throughout pregnancy. In both groups, it actually shows a progressive, linear reduction between the 10th and 40th weeks. Reference ranges constructed for the whole gestational period might be more useful than a single cutoff value for more efficient prevention and management of preterm birth.