Changes of uterocervical angle and cervical length in early and mid-pregnancy and their value in predicting spontaneous preterm birth

Abstract

Objective: To explore the feasibility of transvaginal ultrasound measurement of uterocervical angle (UCA) and cervical length (CL) in early and mid-pregnancy and evaluate their combined prediction of spontaneous preterm birth (sPTB) in singleton pregnancies. Patients and Methods: This retrospective study comprised 274 pregnant women who underwent transvaginal ultrasound measurement of CL in mid-pregnancy (15-23+6 weeks); in 75 among them, CL also had been measured in early-pregnancy (<14 weeks). These 274 pregnant women were further divided into a preterm group (n = 149, <37 weeks gestation) and a control group (n = 125, >37 weeks gestation) according to delivery before or after 37 weeks, respectively. In the preterm group, 35 patients delivered before 34 weeks and the remaining 114 delivered between 34 and 37 weeks. Results: The optimal threshold of CL to predict preterm birth risk in women with <37 weeks gestation was 3.38 cm, and the optimal threshold of the UCA to predict preterm birth risk in the same group of women was 96°. The optimal threshold of CL to predict preterm birth risk in women with <34 weeks gestation was 2.54 cm, while that of the UCA in the same group of patients was 106°. The area under the curve for predicting preterm birth by combining the UCA and CL measurements was greater than that by using the UCA or CL alone (p < 0.01). The sensitivity and specificity for predicting preterm birth at <34 weeks gestation was 71.7% and 86.4%, respectively; and the sensitivity and specificity for predicting preterm birth at <37 weeks gestation was 87.6% and 80.6%, respectively. The difference between the two groups in CL and UCA were not significant in early pregnancy (p > 0.01), but only in mid-pregnancy (p < 0.01). There was a negative correlation between UCA and gestational week at delivery (r = -0.361, p < 0.001) and a positive correlation between CL and gestational week at delivery (r = 0.346, p < 0.001) in mid-pregnancy. The proportion of deliveries at <34 weeks was highest when the UCA was >105°, and the proportion of deliveries between 35 and 37 weeks was highest when the UCA was between 95° and 105°. The proportion of deliveries at <34 weeks was highest when the CL was <2.5 cm. Conclusion: The combination of UCA and CL has a better ability to predict preterm birth than either measurement alone. A more obtuse UCA or a shorter CL is associated with an earlier spontaneous preterm birth. The UCA increases from early to mid-pregnancy, while the CL decreases from early to mid-pregnancy.

Keywords: cervical length; early and mid-pregnancy; spontaneous preterm birth; transvaginal ultrasound examination; uterocervical angle.

FIGURE 1

(A) Time of delivery <34 weeks, CL is 2.44 cm (gestation time: 23 weeks 5 days). (B) Time of delivery between 34 and 37 weeks, CL is 3.32 cm (gestation time: 23 weeks). (C) Time of delivery >37 weeks, CL is 3.6 cm (gestation time: 20 weeks 2 days).

FIGURE 2

The measurement of uterocervical angle (UCA). UCA was calculated as the angle between two lines. The first line was drawn between the internal (I) and external ostium (os) (E). The second line was drawn 3 cm parallel to the lower aspect of the anterior inner uterine wall passing through the end of the first line at the internal os. (A) Time of delivery <34 weeks, UCA 124° (gestation time: 23 weeks and 5 days). (B) Time of delivery between 34 and 37 weeks, UCA 102° (gestation time: 17 weeks). (C) Time of delivery >37 weeks, UCA 91° (gestation time: 17 weeks 1 day).

FIGURE 3

Regression analysis: (A). Plot of UCA in relation to the week of labor in the middle trimester There was a negative correlation between the UCA in mid-pregnancy and gestational week at delivery (r = −0.361, p < 0.001).

FIGURE 4

Receiver operating characteristic curves of evaluating UCA, CL, and gestational age at delivery (A). UCA and CL for sPTB <34 weeks, (B). UCA and CL for sPTB <37 weeks.