A Comparison of the Contractile Properties of Myometrium from Singleton and Twin Pregnancies

Abstract

ObjectiveOver half of twin pregnancies in US and UK deliver prematurely but the reasons for this are unclear. The contractility of myometrium from twin pregnancies has not been directly investigated. The objective of this research was to determine if there are differences in the contractile activity and response to oxytocin, between myometrium from singleton and twin pregnancies, across a range of gestational ages. Furthermore, we wished to determine if contractile activity correlates with increasing level of stretch, using neonatal birth weights as a marker of uterine stretch.MethodsThis was an in vitro, laboratory based study of myometrial contractility in women pregnant with one or two babies, using biopsies obtained from non-labouring women undergoing Caesarean section. Spontaneous, oxytocin-stimulated and depolarization induced contractile activity was compared.ResultsDirect measurements of myometrial contractility under controlled conditions show that the frequency of contractions and responses to oxytocin are significantly increased in twins compared to singletons. The duration of contraction however was significantly reduced. We find that contractile activity correlates with increasing levels of stretch, using neonatal birth weights as a surrogate for uterine stretch, with response to oxytocin being significantly positively correlated with birth weight.ConclusionsWe have found significant differences in contractile properties between myometrium from singleton and twin pregnancies and that increasing uterine stretch can alter the contractile properties of myometrium. We discuss the implication of these findings to preterm delivery and future studies.

Oxytocin: Its Mechanism of Action and Receptor Signalling in the Myometrium

“…Increased or aberrant uterine distension may also help explain the high rates of preterm labour often associated with cases of polyhydramnios and multiple pregnancy , particularly if the uterus is subjected to higher degree of stretch at an earlier time point in gestation. Interestingly, our recent in vitro studies of myometrial contraction from twin pregnancies showed an increased response to oxytocin compared to singleton pregnancies , although OTR expression was not examined. The stimulus for the increased OTR expression that is found in preterm labours where they are not confounded by a large foetus or multiple pregnancy (i.e.…”

Progress in understanding electro-mechanical signalling in the myometrium

“…We have previously reported (Turton et al . ) that stretch may play role in determining the frequency and duration of contraction, as we found that with increasing uterine distension (from greater neonatal birth weight) contractions were of shorter duration but increased frequency.…”

“…) and multiple pregnancy (Turton et al . ). We would also argue that the intellectual drive for research in this area is as compelling as the clinical need.…”

The effect of induction method in twin pregnancies: a secondary analysis for the twin birth study

“…Furthermore, while induction in whom cervical ripening is not required (no PG group) is associated with a lower rate of CS in the case of singleton pregnancies [18, 19], we did not find the same result in twin pregnancies. We postulate that there may be a different mechanism associated with labor and delivery in twins or that the primary higher risk for CS in twins masks this difference [20, 21]. Since CS rate was similar in both groups, we feel this study indicates that all twins in whom induction of labor is indicated should be informed of a significant risk of unplanned CS, regardless of intervention.…”