Effect of maternal position on cervical length measurement in twin pregnancies

To compare cervical length measurements in twin pregnancies obtained from patients in the recumbent and standing positions.

Fifty women with uncomplicated twin pregnancies underwent monthly transvaginal ultrasound examinations for cervical length measurement in the recumbent and standing positions. The correlation between cervical length measurements obtained in the recumbent and standing positions, and between these measurements and gestational age, were examined. The significance of the differences between measurements obtained in the recumbent and standing positions was also analyzed.

Based on data obtained at the first ultrasound examination, there was a significant correlation between cervical length measurements in the recumbent and standing positions (r = 0.77; t = 8.25; P < 0.0001) and both measurements showed a significant inverse correlation with gestational age (recumbent position: r = -0.60, P < 0.0001; standing position: r = -0.46; P = 0.0008). The mean of the differences (standing - recumbent) was -1.8 mm (95% confidence interval = -3.7-0.04; t = -1.96; P = 0.06) and the mean of percentage differences ((standing - recumbent)/recumbent x 100) was -2.9% (95% confidence interval = -8.6-2.7; t = -1.04; P = 0.3). When the data obtained at all examinations were examined by multiple regression analysis, cervical length measurement in the recumbent position was the only parameter that correlated significantly with the percentage difference between cervical length measurements (P < 0.0001).

Cervical length in twin pregnancies decreases with gestation and there is a good correlation between measurements obtained from women in the recumbent and standing positions. No significant changes in cervical length were observed comparing measurements obtained in the two maternal positions.