Frequency and clinical significance of short cervix in patients with preterm premature rupture of membranes

Abstract

Objective: Cervical length measurement has been uggested as a useful tool for predicting intra-amniotic infection/inflammation in preterm labor, but little information is available in the setting of preterm premature rupture of membranes (pPROM). We aimed to determine whether a short cervical length is independently associated with an increased risk of intra-amniotic infection or inflammation and impending preterm delivery in women with pPROM.

Methods: This was a retrospective cohort study involving 171 consecutive singleton pregnant women with pPROM (21+0-33+6 weeks' gestation), who underwent amniocentesis. Amniotic fluid (AF) was cultured, and assayed for interleukin (IL)-6 and IL-8. Cervical length was measured at the time of amniocentesis by transvaginal ultrasonography with an aseptic technique. Short cervical length was defined as a cervical length of ≤15 mm. Intra-amniotic infection was defined as a positive AF culture for microorganisms and intra-amniotic inflammation was defined as elevated AF concentrations of IL-6 or IL-8 (IL-6 ≥1.5 ng/mL and/or IL-8 ≥1.3 ng/mL).

Results: Fifty (29.2%) women had a sonographic cervical length of ≤15mm. On univariate analysis, short cervical length was associated with an increased risk for intra-amniotic infection and/or inflammation; no other parameters studied showed a significant association. Multivariable analyses indicated that short cervical length was significantly associated with a higher risk of impending preterm delivery (within 2 days of measurement, within 7 days of measurement, and before 34 weeks), and remained significant after adjustment for potential confounders.

Conclusion: In women with pPROM, short cervical length is associated with an increased risk for intra-amniotic infection/inflammation and associated with impending preterm delivery, independent of the presence of intra-amniotic infection/inflammation.

Fig 1. Frequency of a short cervix and normal cervical length stratified by gestational age at measurement (P = 0.052 for χ² test across 4 groups).

Closed columns represent a short cervix. Hash-marked columns represent normal cervical length.

Fig 2. Amniotic Fluid (AF) Interleukin-6 (IL-6) and AF IL-8 concentrations of the study population according to the presence or absence of a short cervix (AF IL-6: Median 3.123 ng/ml, interquartile range 0.569 to 16.181 ng/ml vs. median 0.734 ng/ml, interquartile range 0.378 to 4.096 ng/ml, P = 0.013; AF IL-8: Median 2.542 ng/ml, interquartile range 0.935 to 14.407 ng/ml vs. median 1.029 ng/ml, interquartile range 0.389 to 6.509 ng/ml, P = 0.005; respectively).

Fig 3. Kaplan-Meier estimates of measurement-to-delivery interval according to the results of cervical length assessed by ultrasound (using 15 mm as cut-off) in (A) total study population (median, 4.08 days [95% CI, 2.59–5.58] vs. 19.29 days [95% CI, 11.24–27.35]; P <0.001), (B) women without intra-amniotic infection/inflammation (median, 6.83 days [95% CI, 0.00–15.21] vs. 18.54 days [95% CI, 1.96–35.13]; P = 0.012), and (C) women with intra-amniotic infection/inflammation (median, 3.25 days [95% CI, 1.78–4.72] vs. 19.79 days [95% CI, 9.04–30.55]; P = 0.002).