(Posted:10-Jul-2015)

During pregnancy there is marked hypertrophy and hyperplasia of the uterine muscle and the enlargement of the uterus.At term,the length of the uterus measures about 35 cm including cervix.The fundus is wider both transversely and anteroposteriorly than the lower segment.The uterus assumes pyriform or ovoid shape.The cervical canal is occluded by a thick,tenacious,mucus plug. Uterine contraction in labour: Throughout pregnancy there is involuntary spasmodic uterine contractions which are painless and have no effect on dilatation of cervix.The character of the contractions change with the the onset of labour. During contraction,uterus becomes hard and somewhat pushed anteriorly to make the long axis of the uterus in line with that of pelvic axis.Simultaneously,the patient experiences pain which is situated more on the hypogastric region,often radiating to the thighs. Tonus:It is the intrauterine pressure in between contractions.The tonus is of 2-3 mm Hg.During the first stage of labour,it varies from 8-10 mm Hg.It is inversely proportional to the relaxation. Intensity: The intensity gradually increases with advancement of labour untill it becomes maximum in the second stage during delivery of the baby.Intensity is initially influenced probably by hormons but subsequently depend on multiple origin of contraction.Intrauterine pressure is raised to 40-50 mm Hg during first stage and about 100-120 mm Hg in second stage of labour during contractions. Duration: In the first stage,the contraction last for about 30 seconds initially but gradually increase in duration with the progress of labour.Thus in the second stage,the contraction last longer than in the first stage. Frequency: In the early stage of labour,the contractions come at intervals of ten to fifteen minutes.The intervals gradually shorten with advancement of labour untill untill in the second stage;when it comes every two or three minutes. RETRACTION: Retraction is a phenomenon of the uterus in labour in which the muscle fibres are permanently shortened.The uterine muscles have this property to become shortened once and for all.