Objective
To determine whether universal transvaginal ultrasound (TVU) cervical length (CL) screening is indicated in women with prior term births.
Study Design
We conducted a prospective cohort study from Jan. 1, 2012, to June 30, 2013, of singleton gestations between 18 0/7-23 6/7 weeks undergoing TVU CL screening for prediction of spontaneous preterm birth (sPTB). Women with a prior sPTB, with cerclage, and without delivery data available were excluded. Primary outcomes were the incidence of a CL ≤20 mm, and rates of sPTB <37, <34, and <32 weeks gestation among women with prior term births vs nulliparous women.
Results
A total of 1569 women underwent TVU CL screening; 18 women with a prior iatrogenic preterm birth were excluded. Of those screened, 756 (48.7%) had a prior term delivery and 795 (51.3%) were nulliparous. Women with prior term births differed from nulliparous women with respect to age, body mass index, race, smoking status, and prior dilation and curettage. After adjustment for these confounders, there was no statistical difference in the incidence of CL ≤20 mm (0.8 vs 1.4%; adjusted odds ratio, 0.35; 95% confidence interval, 0.12–1.03) among women with prior term births compared with nulliparous women. Rates of sPTB <37, <34, <32 weeks were similar in women with a prior term birth compared with nulliparous women. The overall incidence of sPTB <37 weeks was 3.2% in women with a prior term birth and 5.0% in nulliparous women. When a CL ≤20 mm was identified, 3 of 6 women with prior term birth delivered at <37 weeks compared with 8 of 11 nulliparous women. There were no identified differences between the odds of sPTB between women with a CL ≤20 mm who had a prior term birth compared with nulliparous women.
Conclusion
Women with prior term birth have a trend toward a lower incidence of CL ≤20 mm, compared with nulliparous women. Further studies are needed to determine whether women with prior term births should be included or excluded from TVU CL screening.
The term ‘universal transvaginal (TVU) cervical length (CL) screening’ is somewhat of a misnomer, because it indicates that all women should undergo TVU CL screening at a certain point in pregnancy. In fact, TVU CL should be used only when appropriate. For example, in singletons with a prior spontaneous preterm birth (sPTB), which represent about 7-10% of pregnant women in US, TVU CL is performed every 2 weeks from 16 to 23 6/7 weeks’ gestation, with the option of cerclage placement for CL <25 mm before 24 weeks gestation. On the contrary, in multiple gestations, which represent approximately 3% of US births, TVU CL screening is not effective, because of the lack of a proven intervention once a short CL is identified. Currently, the term ‘universal’ typically refers to the majority of pregnant women (over 85%), which are those carrying singletons without a prior sPTB.
The concept of universal TVU CL screening in this group has been the subject of much debate following the results of 2 randomized trials, which demonstrated a 45% reduction in sPTB when vaginal progesterone was prescribed to these ‘low-risk’ women with a short cervical length (CL). Many ultrasound units have implemented universal TVU CL screening based on the results of these randomized trials, as well as subsequent cost-effectiveness studies. However, critics of universal CL screening raise some important concerns, primarily that there is limited data regarding effectiveness of universal TVU CL screening in the ‘real world’ setting, and that selective screening in certain subgroups of low-risk women may or may not be more effective than ‘universal’ CL screening. Previous studies have demonstrated that a prior term delivery is protective against subsequent sPTB, but limited information exists regarding whether women with a prior term birth have the same risk of a short CL compared with nulliparous women. The objective of this study is to evaluate the incidence of a CL ≤20 mm and rates of sPTB among women with a prior term birth undergoing TVU screening compared with nulliparous women.
Materials and Methods
This prospective cohort study was designed to evaluate outcomes in women undergoing universal TVU CL screening at our institution between Jan. 1, 2012, and June 30, 2013. Clinical questions were formulated before data collection. Our tertiary care academic institution implemented universal TVU CL screening on Jan. 1, 2012; details of our screening program have been previously published. In brief, TVU CL screening was offered to all women with singletons without a prior sPTB who were scheduled for an ultrasound between 18 0/7 and 23 6/7 weeks’ gestation. Women with multiple gestations, with a cerclage in situ, or with a prior sPTB were excluded from universal CL screening because these women are managed differently in our institution, as described above. TVU CL measurements were performed in a standardized fashion according to Cervical Length Education and Review (CLEAR) guidelines, and CL was interpreted according to a predetermined management protocol. Our sonographers have participated in numerous research protocols in which their TVU CL skills had to be certified, and image quality control was in place. For the last 10 years, our full-time sonographers received continuing quality control on TVU CL from attending physicians. All sonographers are currently CLEAR certified.
Our CL management algorithm has been described in prior publications but, in brief, women with CL ≤20 mm before 24 weeks were prescribed vaginal progesterone. Women with a CL ≥25 mm were considered ‘normal’ and no follow-up was recommended. Women with a CL 21-24.9 mm were advised to return for 1 follow-up TVU CL before 24 weeks’ gestation, and if the CL was CL ≤20 mm at that time, vaginal progesterone was prescribed.
Women undergoing TVU CL screening were included in the analysis if they received antenatal care at our institution and had delivery data available. For women who delivered at an outside institution, but were last seen for a prenatal visit at our institution at ≥37 weeks, the gestational age (GA) recorded at the last prenatal visit was used as the GA at delivery in the analysis. We excluded women undergoing termination of pregnancy for fetal anomalies and those with intrauterine fetal demise. Antenatal and delivery records were used to extract outcome data. Our primary outcomes were the incidence of a CL ≤20 mm as well as the incidence of sPTB <37, <34 and <32 weeks’ gestation among women with a prior term birth compared with nulliparous women. Independent samples t test, nonparametric tests, χ 2 test, and logistic regression were performed using SPSS 21.0 (2011, version 21; IBM Corp, Armonk, NY). Individual informed consent was not required because TVU CL screening was implemented as the standard of clinical care in our institution; however, expedited institutional review board approval was obtained.
Results
During the study period, 2558 women were eligible for TVU CL screening, of which 602 (23.5%) eligible women declined or were not offered TVU CL screening for reasons such as a language barrier. A total of 18 women with a prior iatrogenic preterm birth were excluded from analysis (none of whom had a CL <25 mm). Of the 1551 included in the analysis, 756 (48.7%) had a previous term delivery and 795 (51.3%) were nulliparous. The 2 groups were similar with respect to GA at screening and history of cervical conization ( Table 1 ). However, compared with nulliparous women, women with prior term births were older, had higher body mass indices (BMI), were more likely to be black, to smoke tobacco, and to have had a prior dilation and curettage ( Table 1 ). Women with prior term deliveries had a lower incidence of CL ≤15 mm (0.3% vs 0.8%; adjusted odds ratio, 0.17; 95% confidence interval, 0.03–0.95), and there was a nonsignificant lower incidence of CL ≤20 mm (0.8% vs 1.4%; adjusted odds ratio, 0.35; 95% confidence interval, 0.12–1.03). Among women with CL ≤20 mm, 4 of 6 (67%) women with prior term birth received vaginal progesterone and 9 of 11 (81%) nulliparous women received vaginal progesterone. Rates of sPTB were similar in women with a prior term birth compared with nulliparous women ( Table 2 ). The overall incidence of sPTB <37 weeks was 3.2% in women with a prior term birth and 5.0% in nulliparous women; however, when a CL ≤20 mm was identified, 3 of 6 women with prior term birth delivered at <37 weeks compared with 8 of 11 nulliparous women. Compared with nulliparous women, women with a prior term birth with CL ≤20 mm had a nonsignificant trend toward lower rates of sPTB at <37, <34, and <32 weeks’ gestation ( Table 3 ). Among women with a prior term birth who had a CL ≤20 mm, 2 had 1 prior term birth, 2 women had 2 prior term births, and 2 women had 3 prior term births. The sensitivity and positive predictive value of TVU CL ≤20 mm for sPTB <37 weeks was lower among women with a prior term birth compared with nulliparous women ( Table 4 ).
| Demographic | Prior term birth, n = 756 (48.7%) | Nulliparous, n = 795 (51.3%) | P value |
|---|---|---|---|
| Mean maternal age, y | 29.3 (± 5.4) | 26.2 (± 5.8) | < .001 |
| Mean gestational age at TVU CL, wks | 20.3 (± 1.4) | 20.2 (± 1.1) | .63 |
| Median gestational age at delivery (wks ± range) | 39.2 (± 22.4) | 39.5 (± 22.2) | .09 |
| Race/ethnicity | < .001 | ||
| White | 156 (20.6) | 264 (33.2) | |
| Black | 423 (56.0) | 350 (44.0) | |
| Asian | 97 (12.8) | 110 (13.8) | |
| Hispanic | 63 (8.3) | 43 (5.4) | |
| Other/unknown | 17 (2.2) | 28 (3.5) | |
| Mean body mass index, kg/m 2 | 28.2 (± 7.1) | 26.0 (± 6.6) | < .001 |
| Tobacco use | 102 (13.5) | 55 (6.9) | < .001 |
| Prior dilation and curettage | 310 (41) | 207 (26.0) | < .001 |
| Prior cervical excision procedure | 47 (6.2) | 33 (4.2) | .07 |
| Variable | Prior term birth, n = 756 (48.7%) | Nulliparous, n = 795 (51.3%) | aOR a (95% CI) |
|---|---|---|---|
| CL ≤15 mm b | 2 (0.3) | 6 (0.8) | 0.17 (0.03–0.95) |
| CL ≤20 mm b | 6 (0.8) | 11 (1.4) | 0.35 (0.12–1.03) |
| CL ≤25 mm b | 10 (1.3) | 13 (1.6) | 0.51 (0.20–1.30) |
| sPTB <37 wks | 24 (3.2) | 40 (5.0) | 0.61 (0.35–1.10) |
| sPTB <34 wks | 13 (1.7) | 11 (1.4) | 1.00 (0.41–2.44) |
| sPTB <32 wks | 5 (0.7) | 7 (0.9) | 0.49 (0.12–1.71) |
a Adjusted for maternal age, maternal race, body mass index, prior dilation and curettage and smoking status via binary logistic regression
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
