The viscoelastic properties of the cervical mucus plug.

OBJECTIVE To characterize the viscoelastic properties of cervical mucus plugs(CMPs) shed during labor at term. DESIGN Experimental research. SETTING Department of Obstetrics and Gynecology, Aarhus University Hospital, Denmark. POPULATION/SAMPLE Spontaneously shed CMPs from 18 healthy women in active labor. METHODS Viscoelastic properties of CMPs were investigated with a dynamic oscillatory rheometer using frequency and stress sweep experiments within the linear viscoelastic region. MAIN OUTCOME MEASURES The rheological variables obtained were as follows: elastic modulus (G′), viscous modulus (G″) and tan delta (G″/G′). Random-effects regression was used for statistical analysis. RESULTS All CMPs showed solid-like viscoelastic behavior.This was substantiated by the elastic modulus which was three to four times greater than the viscous modulus and by tan delta, which was <1 at all frequencies.Mean tan delta at 0.01 Hz was 0.38 (95% CI 0.34-0.43) and 0.27(95% CI 0.23-0.32) at 1 Hz. The elastic modulus could be described by the relation G′(ω) = K(ω)(A) [mean R2 0.95 (95% CI 0.93-0.98)]. Despite relatively large variation in the rheological properties within CMPs, rheological variables obtained from frequency sweeps differed significantly among CMPs (p < 0.05). CONCLUSION The CMPs are solid-like viscoelastic structures. These rheological characteristics are probably essential for the CMP's ability to form and sustain a plug in the cervical canal during pregnancy, thereby reducing the risk of ascending infections. The technique described here might be used for evaluation of an association between CMP viscoelasticity and preterm delivery.