Transvaginal cervical length and amniotic fluid index: can it predict delivery latency following preterm premature rupture of membranes?




Materials and Methods


The study was conducted from July 2011 through March 2014 at a single perinatal center. This study was approved by the Institutional Review Board at Saint Louis University. This was a prospective observational study in women with PPROM who consented to undergo TVCL measurement after admission.


Eligible women included nonlaboring patients, ages ≥16, with singleton gestation who presented with PPROM between the gestational age (GA) of 23 weeks 5 days–33 weeks 6 days. PPROM was diagnosed by history and physical examination, which included documentation of nitrazine- or fern-positive pooled vaginal fluid obtained by sterile speculum examination. In equivocal cases a placental alpha microgobulin-1 protein assay was performed from the vaginal fluid sample. GA was calculated from the first day of the last normal menstrual period and an ultrasound in early pregnancy when available. Women were excluded prior to enrollment for labor (defined as painful uterine contractions ≥12 in an hour and cervical dilation of >3 cm confirmed by digital examination), for being non-English speaking, or for having had >1 digital examination following PPROM. Following study enrollment women were excluded for a variety of reasons ( Figure 1 ).




Figure 1


Study inclusion characteristics

PPROM , preterm premature rupture of membranes.

Mehra. Cervical length and AFI: can it predict delivery latency PPROM? Am J Obstet Gynecol 2015 .


All women were hospitalized and placed on modified bed rest. TVCL was performed within 72 hours of admission using the CLEAR guidelines. Measurements of the TVCL were taken after visualizing the endocervical canal in its entirety for 3-5 minutes, with an empty maternal bladder. Calipers were placed where the anterior and posterior walls of the cervix were sonographically opposed and the shortest technically best measurements were used. The presence of funneling was noted. AFI was recorded at the time of the TVCL measurement. Prophylactic antibiotics used included ampicillin 2 g intravenously every 6 hours and azithromycin 500 mg intravenously daily for 2 days, followed by oral amoxicillin 250 mg every 8 hours and azithromycin 500 mg daily for 5 days. Two doses of 12 mg betamethasone were given intramuscularly, 24 hours apart. Tocolysis was generally administered during transport. Additional digital examinations were prohibited without visual evidence of cervical change. Expectant management was followed until 34+ weeks’ gestation.


Our primary endpoint was a latency period within 7 days from performance of the TVCL at admission. To provide a more meaningful risk assessment for clinical purposes, TVCL and AFI were analyzed as dichotomous variables as ≤2.0 and >2.0 cm for TVCL, and ≤5 and >5 cm for AFI. Sensitivity, specificity, and predictive values were used to examine whether the presence of TVCL, AFI, or a combination of both characteristics affected the risk of delivery within 7 days.


Comparative analyses were undertaken to determine whether other variables affected latency. Demographic, medical, obstetrical, sonographic, and delivery variables were recorded such as GA at PPROM, history of PPROM or preterm delivery, tobacco and drug use, history of cervical procedures, visual cervical dilation at admission, presence of vaginal bleeding, digital examination performed prior to admission, and presence or absence of funneling at the TVCL assessment.


We based our preliminary sample size estimates on previously published PPROM data from Tsoi et al. In that study of women with a CL ≤2.0 cm, 76% delivered within 7 days compared to only 29% of women with a TVCL >2.0 cm. To detect a similar magnitude of difference with a power of 0.8, alpha <0.05, a sample size of at least 18 women per TVCL comparison groups were required.


Differences in demographic characteristics, medical/obstetrical history, and clinical/delivery characteristics were compared between women who delivered ≤7 days vs >7 days using χ 2 , Fisher exact test, and independent Students t test for continuous variables that were normally distributed. The nonparametric Kolmogorov-Smirnov test was used for continuous variables that were not normally distributed. Cox regression was used to compare the relationships of latency from PPROM to delivery and from CL to delivery. The independent predictability of statistically significant univariate characteristics on latency from initial TVCL was examined by multiple logistic regression. Sensitivity, specificity, and predictive value were calculated for TVCL (≤2.0 cm and >2.0 cm) and AFI (≤5.0 cm and >5.0 cm) in relation to the latency period of 7 days. Positive predictive value (PPV) was defined as the probability for delivery within 7 days from the TVCL. Negative predictive value (NPV) was defined as the probability of remaining pregnant >7 days. A P value < .05 was used to denote statistical significance. All analyses were performed using software (SPSS, Version 21.0; IBM Corp, Armonk, NY).




Results


In all, 129 singleton women with suspected PPROM consented for the study. Figure 1 illustrates the reasons for postconsent exclusions: 106 were included for final analysis.


Subjects were between 18-41 years of age, with approximately 90% of cases occurring <35 years. The body mass index (BMI) ranged between 19.6–64.8 kg/m 2 . All transported women had corticosteroids, tocolysis, and latency antibiotics initiated for transfer. Approximately one third of women had a single vaginal examination performed at the referring hospital prior to the TVCL assessment. A third of women had a closed cervix visualized on sterile speculum examination on admission. In all, 68 women (64%) had a TVCL performed within 1 day of PPROM, 92 (87%) within 2 days, and 103 (97%) within 3 days. The mean TVCL was 2.5 ± 1.3 cm (1 SD); 29% had a TVCL ≤1.5 cm and 19%, ≤1.0 cm. Of cases, 10% had anhydramnios at admission. Using a Cox regression we assessed latency interval from performance of the TVCL in relation to latency interval from PPROM. Accordingly there was no significant difference in delivery rates within 7 days of PPROM and 7 days of initial TVCL: 49/106 (46.2%) and 51/106 (48.1%), respectively.


The univariate relationships of demographic, medical, obstetrical, sonographic, and delivery variables for ≤7 days and >7 days of latency from the TVCL measurement are summarized in Tables 1-3 . CL and AFI were each significantly associated with delivery within 7 days. The median TVCL was significantly shorter and an AFI (≤5 cm) was significantly more frequent in women who delivered ≤7 days. A latent period ≤7 days was also significantly associated with a later GA at TVCL, prior preterm birth, prior PPROM, illicit drug use, and uterine contractions.



Table 1

Demographic/medical/obstetric data by delivery latency at 1 week





















































































































































Demographic ≤7 d
(n = 51)
>7 d
(n = 55)
P value
Maternal age, y 25.0 (22.0–32.0) 25.0 (20.0–30.0) 1.00
Nulliparous 25 49.0 24 43.6 .58
Race
Caucasian 26 51.0 33 60.0
African American 23 45.1 21 38.2 .58
Other 2 3.9 1 1.8
Body mass index, kg/m 2 29.3 (24.5–33.8) 27.8 (23.3–35.2) .21
Smoking 21 41.2 19 34.5 .48
Illicit drug use 10 19.6 3 5.5 < .05
Insurance
Private 11 21.6 13 24.1 .10
Medicaid 33 64.7 25 46.3
Self-pay 7 13.7 16 29.6
Medical history
Asthma 10 19.6 5 9.1 .12
Obstetrical history
Pregnancy with PPROM 12 23.5 2 3.6 < .01
Preterm birth 17 33.3 6 10.9 < .01
Cervical incompetence 3 5.9 2 3.6 .67
LEEP or cone biopsy 5 9.8 4 7.3 .74

Data are expressed as median (interquartile range) for continuous variables, and as number and percentage for categorical variables. Insurance was unknown for 1 woman.

LEEP , loop electrosurgical excision procedure; PPROM , preterm premature rupture of membranes.

Mehra. Cervical length and AFI: can it predict delivery latency PPROM? Am J Obstet Gynecol 2015 .


Table 2

Clinical and sonographic characteristics by delivery latency at 1 week



































































































































































Characteristic ≤7 d
(n = 51)
>7 d
(n = 55)
P value
Maternal transports 36 70.6 43 79.6 .28
Gestational age at PPROM, wk 31.4 (29.4–33.0) 28.7 (26.9–31.0) < .001
Gestational age at first cervical length, wk 31.6 (29.4–33.1) 28.9 (27.0–31.3) < .001
Duration from PPROM to first cervical length, d 1.0 (1.0–2.0) 1.0 (1.0–2.0) 1.00
Digital cervical examinations following PPROM
0 31 60.8 38 69.1 .37
1 20 39.2 17 30.9
Cervical dilation at admission, cm 1.0 (0.0–2.0) 1.0 (0–1.0) .21
Vaginal bleeding prior to PPROM 10 19.6 7 12.7 .34
Uterine contractions any time before PPROM 18 35.3 10 18.2 < .05
Uterine contractions immediately before PPROM 14 27.5 5 9.1 < .05
Uterine contractions after PPROM 27 52.9 14 25.9 < .01
Positive group-B streptococcus culture 12 24.0 15 27.3 .70
Positive gonococcus or chlamydia DNA 2 3.9 3 5.6 1.00
Cervical length, cm 2.1 (0.9–3.1) 3.0 (1.9–3.7) < .01
Amniotic fluid index, cm 3.5 (1.3–5.3) 5.2 (2.7–8.4) < .05
Funneling 8 16.0 13 23.6 .33
Fetal presentation at first ultrasound
Cephalic 37 72.5 37 67.3 .41
Breech 13 25.5 14 25.5
Transverse 0 0.0 03 5.5
Funic 1 2.0 1 1.8

Data are expressed as median (interquartile range) for continuous variables, and as number and percentage for categorical variables. Cervical dilation at admission was unknown for 2 women. Uterine contractions after PPROM, group-B streptococcus, and funneling were unknown for 1 woman.

PPROM , preterm premature rupture of membranes.

Mehra. Cervical length and AFI: can it predict delivery latency PPROM? Am J Obstet Gynecol 2015 .


Table 3

Delivery characteristics by delivery latency at 1 week

























































































































Characteristic ≤7 d
(n = 51)
>7 d
(n = 55)
P value
Gestational age at delivery, wk 31.9 (29.4–33.9) 31.5 (29.3–33.5) .69
Birthweight, g 1685 (1415–2116) 1723 (1348–2183) .28
Duration from PPROM to delivery, d 4.0 (3.0–6.0) 16.0 (11.0–22.3) < .001
Duration from first cervical length to delivery, d 3.0 (2.0–4.0) 15.0 (10.0–20.0) < .001
Cord prolapse after PPROM 2 3.9 2 3.7 1.00
Delivery
Spontaneous delivery 39 76.5 41 75.9
Indicated delivery 9 17.6 6 11.1 .34
Induced for ≥34 wk 3 5.9 7 13.0
Mode of delivery
Vaginal 33 64.7 32 59.3 .57
Cesarean 18 35.3 22 40.7
Clinical chorioamnionitis 8 15.7 12 22.7 .39
Histological chorioamnionitis 31 70.5 37 80.4 .27
Funisitis 17 38.6 25 54.3 .14
Endometritis 1 2.0 3 5.0 .62

Data are expressed as median (interquartile range) for continuous variables, and as number and percentage for categorical variables. Delivery outcomes were unknown for 1 woman. Placental findings were unknown for 16 women.

PPROM , preterm premature rupture of membranes.

Mehra. Cervical length and AFI: can it predict delivery latency PPROM? Am J Obstet Gynecol 2015 .


Using significant variables from univariate analyses a stepwise multiple logistic regression model was performed ( Table 4 ).



Table 4

Final multiple logistic regression models predicting delivery latency for 104 women with PPROM




































≤7 d from initial cervical length
Characteristic OR 95% CI P value
Prior pregnancy with PPROM 10.62 1.84–61.45 < .01
Gestational age at cervical length, wk 1.35 1.12–1.63 < .01
Uterine contractions after PPROM 5.55 1.91–16.11 < .01
Cervical length, cm 0.65 0.44–0.97 < .05
Amniotic fluid index (≤5 cm) 4.69 1.58–13.93 < .01

Final multiple logistic regression model predicting delivery latency for each time period was generated from characteristics that were statistically significant in univariate group comparisons. Amniotic fluid index was entered as dichotomous categorical variable (≤5 cm and >5 cm). Final model was based on 104 women, since uterine contractions after PPROM and amniotic fluid index were unknown for 1 woman each. Only gestational age at cervical length (and not at PPROM) was included in model.

CI , confidence interval; OR , odds ratio; PPROM , preterm premature rupture of membranes.

Mehra. Cervical length and AFI: can it predict delivery latency PPROM? Am J Obstet Gynecol 2015 .


We examined screening parameters for TVCL and AFI as dichotomous variables for the prediction of the latent period of 1 week from TVCL ( Table 5 ). In all, 42 women (40%) had a TVCL ≤2 cm while 62 (59%) had an AFI ≤5 cm. Of 105 women, 26 (25%) had a combination of both TVCL ≤2 cm and AFI ≤5 cm, while 27 of 105 women (26%) had neither characteristic. Having a combination of low TVCL and low AFI did not increase the PPV of delivery within 7 days (58% for low TVCL/low AFI compared to either characteristic alone, 62% for low TVCL, and 58% for low AFI) ( Table 5 ). Only 3 of 27 women (11%) who had neither characteristic delivered within 7 days. The NPV overall for TVCL >2 cm was 61%. The NPV changed when TVCL >2 cm was analyzed together with an AFI ≤5 cm (42%) and AFI >5 cm (89%) ( Table 5 ).



Table 5

Predicting delivery latency within 7 days following PPROM by each factor


































Variable Sensitivity Specificity PPV NPV
TVCL ≤2 vs >2 cm (n = 106) 26/51 = 51% 39/55 = 71% 26/42 = 62% 39/64 = 61%
AFI ≤5 vs >5 cm (n = 105) 36/50 = 72% 29/55 = 53% 36/62 = 58% 29/43 = 67%
TVCL <2 vs >2 cm in women with AFI ≤5 cm (n = 62) 15/36 = 42% 15/26 = 58% 15/26 = 58% 15/36 = 42%
TVCL <2 vs >2 cm in women with AFI >5 cm (n = 43) 11/14 = 76% 24/29 = 83% 11/16 = 69% 24/27 = 89%

Prevalence of delivery <1 wk is 48%. Sensitivity, specificity, and predictive values were calculated for TVCL and AFI in relation to latency period of 7 d. PPV was defined as probability for delivery within 7 d from test. NPV was defined as probability of remaining pregnant >7 d from test.

AFI , amniotic fluid index; NPV , negative predictive value; PPV , positive predictive value; TVCL , transvaginal cervical length.

Mehra. Cervical length and AFI: can it predict delivery latency PPROM? Am J Obstet Gynecol 2015 .


Tables 6 and 7 describe the analysis of these testing parameters stratified by a GA in women ≤30 and >30 weeks, respectively. Compared to the overall cohort the NPV of these tests were enhanced in women ≤30 weeks at PPROM. In women >30 weeks at PPROM the PPV of delivery within a week was enhanced. These findings further highlight the importance of GA as an independent risk factor for latency.


May 6, 2017 | Posted by in GYNECOLOGY | Comments Off on Transvaginal cervical length and amniotic fluid index: can it predict delivery latency following preterm premature rupture of membranes?

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