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 (P- PROM) 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.
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