Abstract
Uterine wall tension is thought to be an important determinant of the onset of labor in pregnant women. We characterize human uterine wall tension using ultrasound from the second trimester of pregnancy until parturition and compare preterm, term and twin pregnancies. A total of 320 pregnant women were followed from first antenatal visit to delivery during the period 2000–2004 at the John Hunter Hospital, NSW, Australia. The uterine wall thickness, length, anterior-posterior diameter and transverse diameter were determined by serial ultrasounds. Subjects were divided into three groups: women with singleton pregnancies and spontaneous labor onset, either preterm or term and women with twin pregnancies. Intrauterine pressure results from the literature were combined with our data to form trajectories for uterine wall thickness, volume and tension for each woman using the prolate ellipsoid method and the groups were compared at 20, 25 and 30 weeks gestation. Uterine wall tension followed an exponential curve, with results increasing throughout pregnancy with the site of maximum tension on the anterior wall. For those delivering preterm, uterine wall thickness was increased compared with term. For twin pregnancies intrauterine volume was increased compared to singletons (), but wall thickness was not. There was no evidence for increased tension in those delivering preterm or those with twin gestations. These data are not consistent with a role for high uterine wall tension as a causal factor in preterm spontaneous labor in singleton or twin gestations. It seems likely that hormonal differences in multiple gestations are responsible for increased rates of preterm birth in this group rather than increased tension.
Highlights
During pregnancy the uterus grows from a 70-gram near solid organ with a narrow cavity to a hollow tubular organ weighing 1100 grams
As data on intrauterine pressure in both singletons and twins was already available in the literature we did not consider it ethical to repeat these measurements; we used pressure measurements throughout gestation from the literature combined with our ultrasonography measures of uterine size, shape and wall thickness throughout pregnancy to construct a uterine wall tension trajectory based on a prolate ellipsoid as a better approximation of the uterine shape [10]
In their study after the second trimester there was a significant decline in the thickness of the myometrium in the anterior aspect of the lower uterine segment, which was not examined in our study
Summary
During pregnancy the uterus grows from a 70-gram near solid organ with a narrow cavity to a hollow tubular organ weighing 1100 grams. A study by Ulmsten et al [8] dealt with intrapartum myometrial tension in term, non-laboring women where induction of labor was achieved with oxytocin infusion. They reported that women with low myometrial tension failed induction of labor. As data on intrauterine pressure in both singletons and twins was already available in the literature we did not consider it ethical to repeat these measurements; we used pressure measurements throughout gestation from the literature combined with our ultrasonography measures of uterine size, shape and wall thickness throughout pregnancy to construct a uterine wall tension trajectory based on a prolate ellipsoid as a better approximation of the uterine shape [10]. Our specific objectives were to (a) characterize uterine wall thickness, intrauterine volume and maximum uterine wall tension trajectories from 20 weeks gestation to delivery for preterm and term singletons with spontaneous labor onset and for twin pregnancies and (b) assess group differences (preterm versus term, twin versus term) in uterine wall thickness, intrauterine volume and maximum uterine wall tension at 20, 25 and 30 weeks gestation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
