A short review of twin pregnancy and how oxytocin receptor expression may differ in multiple pregnancy.

During a multiple pregnancy, the mother and her fetuses are exposed to a variety of risks during both pregnancy and labour. The most notable of these risks is that of pre-term labour and its associated sequelae. Whilst much research has been directed towards understanding the mechanisms of uterine contractility, very little research has focussed on how contractility in multiple pregnancy differs from contractility in the singleton pregnancy. The aim of this paper is to review the changing prevalence and risks of a twin pregnancy, as well as reviewing what is known about myometrium from multiple pregnancies. The paper ends by discussing how oxytocin receptor expression may differ in twin pregnancy, based on the evidence of animal models, as well as presenting our own evidence of how oxytocin affects myometrium from twin pregnancies. We highlight the lack of the basic information needed to characterize human myometrium in twin pregnancies. Of particular note is the lack of supporting data for the hypothesis that stretch is responsible for earlier activation of the uterus in multiple pregnancy. New hypotheses based on increased experimental work are called for. Such information may throw light on specific mechanisms leading to the increased incidence of pre-term delivery in twins.