Age-related changes in thickness of anterior lower uterine segment in normal singleton pregnancy during 20-35 weeks'...

To observe age-related changes in the anterior lower uterine segment (LUS) thickness in normal pregnancy from 20 to 35 weeks' gestation.

Subjects were 235 uncomplicated singleton cases that underwent single ultrasound examination at 4-week intervals during 20-35 weeks' gestation. Sagittal LUS sections were evaluated with transvaginal ultrasonography. Anterior LUS thickness (Th) was measured every centimeter from the lowest bladder point (Th0cm) to 4 cm from that point (Th4cm). Th values were standardized by dividing by the Th0cm value. Intragroup comparisons of standardized Th values and intergroup comparisons of actual Th values were made according to gestational age. Statistical analyses were performed with the Kruskal-Wallis and Tukey honest standard deviation tests; significance was set at p < 0.05.

In the 20-23-, 24-27- and 32-35-week groups, standardized Th decreased from Th0cm to Th2cm; in the 28-31-week group standardized Th decreased from Th0cm to Th3cm. Median Th3cm values decreased from 5.0 mm at 20-23 weeks to 3.0 mm at 28-31 weeks, but remained unchanged thereafter.

The anterior LUS gradually thinned from Th0cm to Th3cm at 20-35 weeks' gestation. Th3cm became increasingly thin between 20-23 and 28-31 weeks' gestation.