Background
Transvaginal measurement of cervical length (CL) has been advocated as a screening tool to prevent preterm birth, but controversy remains regarding the overall utility of universal screening.
Objective
We aimed to evaluate the acceptability of a universal CL screening program. Additionally we evaluated risk factors associated with declining screening and subsequent delivery outcomes of women who accepted or declined screening.
Study Design
This was a retrospective cohort study of transvaginal CL screening at a single institution from July 1, 2011, through December 31, 2014. Institutional protocol recommended transvaginal CL measurement at the time of anatomic survey between 17-23 weeks in all women with singleton, viable pregnancies, without current or planned cerclage, with patients able to opt out. Patients with CL ≤20 mm were considered to have clinically significant cervical shortening and were offered treatment. We assessed acceptance rate, risk factors for declining CL screening, and the trend of acceptance of CL screening over time. We also calculated the prevalence of CL ≤25, ≤20, and ≤15 mm, and estimated the association between CL screening and spontaneous preterm birth.
Results
Of 12,740 women undergoing anatomic survey during the study period, 10,871 (85.3%; 95% confidence interval [CI], 84.7–85.9%) underwent CL screening. Of those, 215 (2.0%) had a CL ≤25 mm and 131 (1.2%) had a CL ≤20 mm. After the first 6 months of implementation, there was no change in rates of acceptance of CL screening over time ( P for trend = .15). Women were more likely to decline CL screening if they were African American (adjusted odds ratio [aOR], 2.17; 95% CI, 1.93–2.44), obese (aOR, 1.18; 95% CI, 1.06–1.31), multiparous (aOR, 1.45; 95% CI, 1.29–1.64), age <35 years (aOR, 1.24; 95% CI, 1.08–1.43), or smokers (aOR, 1.42; 95% CI, 1.20–1.68). Rates of spontaneous preterm birth <28 weeks were higher in those who declined CL screening (aOR, 2.01; 95% CI, 1.33–3.02).
Conclusion
Universal CL screening was implemented successfully with 85% of women screened. Overall incidence of short cervix was low and women with significant risk factors for preterm birth were more likely to decline screening. Patients who declined CL screening were more likely to be African American, obese, multiparous, age <35 years, and smokers. Rates of early, but not late, spontaneous preterm birth were significantly higher among women who did not undergo CL screening.
Introduction
The incidence of preterm birth in the United States has remained stable despite efforts aimed at preterm birth reduction. Of the nearly 400,000 babies delivered prematurely annually, approximately two-thirds are spontaneous preterm births, with an estimated 15% occurring in women with a history of preterm birth. There remains an urgent need to develop effective strategies for screening and prevention of preterm birth among those with and without a history of preterm birth.
Women who are identified as having a short cervix in the midtrimester are at increased risk of delivering preterm. Recent studies have shown vaginal progesterone reduces the incidence of spontaneous preterm birth <34 weeks’ gestation by approximately 45% in women with a short cervix. With potentially effective treatments available, many have advocated for implementation of universal transvaginal cervical length (TVCL) screening to identify women at risk of preterm birth. However, controversy exists over the utility of TVCL screening in low-risk patients. Advocates for TVCL screening point to the efficacy of interventions when short cervix is identified, the potential cost-effectiveness of screening, and the limited harm with TVCL screening. Opponents question the standardization and reproducibility of TVCL measurement, question whether screening and intervention will provide meaningful risk reduction and remain cost-effective outside of clinical trials, and raise concerns regarding “indication creep,” with increasing interventions in situations where benefit is unproven. In spite of this controversy, there has been rapid uptake of TVCL screening programs, with the American Congress of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine publishing clinical guidelines suggesting, but not mandating, implementation of universal TVCL screening and treatment with either vaginal progesterone or cerclage as indicated if the cervix is short. To date, there have been few publications on the implementation of a universal cervical length (CL) screening program, uptake among patients, and effectiveness of universal TVCL screening.
Our primary aim was to evaluate the acceptability and uptake of a universal TVCL screening program. Our secondary aim was to evaluate risk factors associated with declining CL measurement. Additionally, we evaluated the likelihood of preterm delivery in women who declined CL measurement as compared to women who accepted CL measurement.
Materials and Methods
We conducted a retrospective cohort study of all patients undergoing anatomy screening in the midtrimester at a single institution from July 1, 2011, through Dec. 31, 2014. Beginning in July 2011, institutional protocol recommended TVCL measurement in all women with singleton, viable pregnancies, without current or planned cerclage at the time of anatomic survey performed between 17 0/7 and 23 6/7 weeks’ gestation, with patients able to opt out. The study was conducted after approval from the Washington University School of Medicine Human Research Protection Office.
CL measurements are performed by trained ultrasonographers using the standard technique. Briefly, after the patients’ bladder has been emptied, the probe is inserted into the anterior fornix of the vagina. A sagittal view of the cervix is obtained with a long axis view of the echogenic endocervical mucosa along the length of the cervical canal. The probe is withdrawn until the image is blurred and then reinserted, avoiding excessive pressure. The image is enlarged to occupy two thirds of the screen and 3 measurements are obtained from the internal to external os along the entire endocervical canal, with the shortest, best measurement used.
Patients with CL ≤20 mm were considered to have clinically significant cervical shortening and offered treatment. Women with CL between 21-25 mm were considered to have borderline short cervix and returned for repeat CL measurements <24 weeks. For the purposes of this study, only the shortest CL measured <23 6/7 weeks was used for analysis.
Details regarding maternal and obstetrical history, pregnancy complications, delivery outcomes, and neonatal characteristics for women obtaining ultrasounds at our institution are collected and entered into a prospective computerized database in an ongoing manner. This database was originally created in 1990 and has been validated and maintained since that time by dedicated perinatal research nurses. Maternal demographic and pregnancy information are entered prospectively at the time of ultrasound exam at our institution. Neonatal and pregnancy outcome information are obtained using electronic medical records and telephone contact with the patient or referring provider as needed. Maternal demographics including age, race/ethnicity, tobacco use, body mass index, and gestational age at the time of ultrasound were obtained from this database. Race/ethnicity was defined as Caucasian (used as the reference group), African American, Hispanic, or other and was based on self-report. Those who did not report race/ethnicity were noted. Additional information regarding CL, pregnancy complications, mode of delivery, and neonatal outcomes was collected from the perinatal database. Trained research staff reviewed charts of patients with CL ≤20 mm to extract further data on treatments received. Gestational age was determined based on last menstrual period if first-trimester ultrasound agreed with the estimated date of confinement (EDC) within 7 days or second-trimester ultrasound agreed with EDC within 14 days. If the due date differed by >7 days in the first trimester or 14 days in the second trimester, or if the last menstrual period was unknown, the EDC was changed to that calculated from earliest available ultrasound.
We calculated the acceptance rate of CL screening overall and for each year since implementation. We also evaluated risk factors for declining CL screening by comparing demographic and pregnancy characteristics between women who underwent CL screening and those who declined. We also compared rates of spontaneous preterm birth (>20 weeks’ but <37, 34, 28, and 24 weeks’ gestation) between the 2 groups for those patients with delivery data available. Spontaneous preterm birth included all patients with spontaneous labor or preterm premature rupture of membranes resulting in delivery. The analysis was repeated limited to women without a history of preterm birth. Additionally, the prevalence of short cervix was determined in our population and was defined as a CL ≤20 mm, with prevalence ≤25 mm and ≤15 mm also determined.
Data analysis was performed using descriptive and bivariate statistics. Normality of distribution for continuous variables was tested using histograms and the Kolmogorov-Smirnov test. An unpaired Student t test or Wilcoxon rank sum test was then used as appropriate. The χ 2 or Fisher exact tests were used for categorical variables as appropriate. A P value of <.05 was considered significant. A multivariable model including age <35 years, gestational age at ultrasound, race/ethnicity, tobacco, obesity, multiparity, and history of preterm birth was used to determine risk factors for declining CL screening. The χ 2 test of trend was used to assess for changes in acceptability of TVCL screening over time. Multivariable logistic regression was used to estimate of the impact of CL screening on preterm birth. The final models controlled for African American race, tobacco use, and a history of preterm birth. Goodness of fit of the final model was tested using the Hosmer-Lemeshow test.
Materials and Methods
We conducted a retrospective cohort study of all patients undergoing anatomy screening in the midtrimester at a single institution from July 1, 2011, through Dec. 31, 2014. Beginning in July 2011, institutional protocol recommended TVCL measurement in all women with singleton, viable pregnancies, without current or planned cerclage at the time of anatomic survey performed between 17 0/7 and 23 6/7 weeks’ gestation, with patients able to opt out. The study was conducted after approval from the Washington University School of Medicine Human Research Protection Office.
CL measurements are performed by trained ultrasonographers using the standard technique. Briefly, after the patients’ bladder has been emptied, the probe is inserted into the anterior fornix of the vagina. A sagittal view of the cervix is obtained with a long axis view of the echogenic endocervical mucosa along the length of the cervical canal. The probe is withdrawn until the image is blurred and then reinserted, avoiding excessive pressure. The image is enlarged to occupy two thirds of the screen and 3 measurements are obtained from the internal to external os along the entire endocervical canal, with the shortest, best measurement used.
Patients with CL ≤20 mm were considered to have clinically significant cervical shortening and offered treatment. Women with CL between 21-25 mm were considered to have borderline short cervix and returned for repeat CL measurements <24 weeks. For the purposes of this study, only the shortest CL measured <23 6/7 weeks was used for analysis.
Details regarding maternal and obstetrical history, pregnancy complications, delivery outcomes, and neonatal characteristics for women obtaining ultrasounds at our institution are collected and entered into a prospective computerized database in an ongoing manner. This database was originally created in 1990 and has been validated and maintained since that time by dedicated perinatal research nurses. Maternal demographic and pregnancy information are entered prospectively at the time of ultrasound exam at our institution. Neonatal and pregnancy outcome information are obtained using electronic medical records and telephone contact with the patient or referring provider as needed. Maternal demographics including age, race/ethnicity, tobacco use, body mass index, and gestational age at the time of ultrasound were obtained from this database. Race/ethnicity was defined as Caucasian (used as the reference group), African American, Hispanic, or other and was based on self-report. Those who did not report race/ethnicity were noted. Additional information regarding CL, pregnancy complications, mode of delivery, and neonatal outcomes was collected from the perinatal database. Trained research staff reviewed charts of patients with CL ≤20 mm to extract further data on treatments received. Gestational age was determined based on last menstrual period if first-trimester ultrasound agreed with the estimated date of confinement (EDC) within 7 days or second-trimester ultrasound agreed with EDC within 14 days. If the due date differed by >7 days in the first trimester or 14 days in the second trimester, or if the last menstrual period was unknown, the EDC was changed to that calculated from earliest available ultrasound.
We calculated the acceptance rate of CL screening overall and for each year since implementation. We also evaluated risk factors for declining CL screening by comparing demographic and pregnancy characteristics between women who underwent CL screening and those who declined. We also compared rates of spontaneous preterm birth (>20 weeks’ but <37, 34, 28, and 24 weeks’ gestation) between the 2 groups for those patients with delivery data available. Spontaneous preterm birth included all patients with spontaneous labor or preterm premature rupture of membranes resulting in delivery. The analysis was repeated limited to women without a history of preterm birth. Additionally, the prevalence of short cervix was determined in our population and was defined as a CL ≤20 mm, with prevalence ≤25 mm and ≤15 mm also determined.
Data analysis was performed using descriptive and bivariate statistics. Normality of distribution for continuous variables was tested using histograms and the Kolmogorov-Smirnov test. An unpaired Student t test or Wilcoxon rank sum test was then used as appropriate. The χ 2 or Fisher exact tests were used for categorical variables as appropriate. A P value of <.05 was considered significant. A multivariable model including age <35 years, gestational age at ultrasound, race/ethnicity, tobacco, obesity, multiparity, and history of preterm birth was used to determine risk factors for declining CL screening. The χ 2 test of trend was used to assess for changes in acceptability of TVCL screening over time. Multivariable logistic regression was used to estimate of the impact of CL screening on preterm birth. The final models controlled for African American race, tobacco use, and a history of preterm birth. Goodness of fit of the final model was tested using the Hosmer-Lemeshow test.
Results
Of 12,740 women undergoing anatomic screening at the midtrimester, 10,871 (85.3%; 95% confidence interval [CI], 84.7–85.9%) underwent TVCL screening, with 1869 (14.7%; 95% CI, 14.1–15.3%) declining cervical screening ( Figure ). Basic characteristics of the cohort are seen in Table 1 . Rates of acceptance of CL screening increased from 77.4% (95% CI, 75.4–79.2%) in 2011 when universal TVCL screening was implemented to 86.7% (95% CI, 85.5–87.8%) in 2012, 85.6% (95% CI, 84.4–86.7%) in 2013, and 87.8% (95% CI, 86.3–88.9%) in 2014. There was no statistically significant change in acceptance of CL screening from 2012 through 2014 ( P for trend = .15). Women were more likely to decline CL screening if they were African American, Hispanic, other race/ethnicity, or if they did not report race/ethnicity when compared to Caucasian patients. Women were also more likely to decline CL screening if they were obese, multiparous, age <35 years, or smokers ( Table 2 ). Similar risk factors were identified when analysis was limited to only those women without a history of preterm birth ( Supplemental Table 1 ).
