Sonographic myometrial thickness predicts the latency interval of women with preterm premature rupture of the membranes and oligohydramnios.

OBJECTIVE

Term labor is associated with global thinning of the myometrium. We hypothesized that a thickened myometrium at the time of preterm premature rupture of membranes (PPROM) predicts less myometrial wall stress and, consequently, a longer latency interval.

STUDY

DESIGN

Myometrial thickness was measured prospectively in 76 pregnant women enrolled in the following groups: PPROM (n=28, mean [range], gestational age [GA]: 29.5 weeks [w] [21.0 w-33.0 w]), preterm nonlabor control group (P-CTR), (n=21, GA: 27.5 w [23.0 w-32.0 w]) and term nonlabor control (T-CTR) (n=27, GA: 38.6 w [37.0 w-41.6 w]). All PPROM women had oligohydramnios (AFI: 1.4 cm [0.0 cm-5.1 cm]). MT was measured ultrasonographically at the midanterior, fundal, posterior, and lower uterine segment wall in cases and controls with an intraoperator variability <10%.

RESULTS

Women in the PPROM group displayed uniform thickness of the uterine body (mean +/- SEM, anterior: 10.6 +/- 0.6 mm, fundal: 10.7 +/- 0.7 mm, posterior: 8.9 +/- 0.5 mm, P=.078). At midanterior site the myometrium of the PPROM group was thicker compared to both P-CTR (P < .001) and T-CTR (P=.025) groups. This difference was preserved at the fundus (PPROM vs P-CTR, P < .001; PPROM vs T-CTR, P=.015). There was a positive correlation between fundal MT and latency period (r=0.43, P=0.02) that persisted after adjusting for GA (P=.04). A fundal MT less than 12.1 mm was 93.7% sensitive and 63.6% specific for the identification of women whose latency period was less than 120 hours.

CONCLUSION

Significant thickening of the anterior and fundal walls of the uterus follows PPROM. A thick myometrium in nonlaboring patients with PPROM is associated with longer latency interval. Sonographic evaluation of MT may represent an alternative clinical tool for the prediction of a short latency interval in women with PPROM.