CHARACTERISTICS OF LABOUR
Labour is defined as a period characterised by the presence of regular and painful uterine contractions accompanied by cervical effacement and evident and progressive cervical dilatation that results in the expulsion of the foetus from the maternal wound.
Labour consists of four stages or periods extending from its beginning to the first hours of the puerperium:
- Stage 1 or dilatation period: interval between the start of labour and complete cervical dilation.
- Stage 2 or expulsion period: interval between complete cervical dilatation and expulsion of the foetus.
- Stage 3 or birth period: interval between the expulsion of the foetus and the expulsion of the placenta.
- Stage 4 or post-birth period: interval between the expulsion of the placenta and the mother’s complete stabilisation.
The progress of labour, from its beginning to the expulsion of the foetus is also determined by several factors, being the most important:
- Age– Parity – Anthropometric features of the pregnant woman
- Premature rupture of the membranes
- Intensity, quality and coordination of uterine contractility.
- Resistance of the uterine neck to stretching and dilation.
- Capacity of expulsive auxiliary forces (pushing reflex)
- Resistance presented by the pelvic floor to the distension caused by the descend of the foetus.
- Size and localisation of the foetus.
- Anatomical features of the human pelvis.
- Type of labour (spontaneous or induced).
- Obstetrical and/or aesthetic management.
A normal labour requires good concordance between the size of the foetus and the dimensions of the maternal pelvis and a good relationship between uterine contractions and the degree of dilatation of the uterine orifice.
The osseous walls of the pelvis constitute the so-called “osseous birth canal” which is composed of three fundamental parts: the upper narrowing space, the centre or mid pelvis and the lower narrowing space. In practice, assessment of pelvic dimensions is performed by determining the anteroposterior and transverse diameters of the upper and mid narrowing. The relation between these parameters and the ecographic foetal cephalometry (foetal dimensions) dictates the obstetrical management to be followed during the labour process.
