Question

Provides an accurate pathophysiology regarding labor and delivery. Describes how it pertains to the patient and the patient’s presentation.

Answer 1

The last few hours of human pregnancy are characterized by forceful and painful uterine contractions that effect cervical dilatation and cause the fetus to descend through the birth canal. There are extensive preparations in both the uterus and cervix long before this. During the first 36 to 38 weeks of normal gestation, the myometrium is in a preparatory yet unresponsive state. Concurrently, the cervix begins an early stage of remodeling—termed softening—yet maintains structural integrity. Following this prolonged uterine quiescence, there is a transitional phase during which myometrial unresponsiveness is suspended, and the cervix undergoes ripening, effacement, and loss of structural integrity.

Physiology of Normal labor

Emanuel Friedman in his elegant treatise on labor (1978) stated correctly that "the clinical features of uterine contractions namely frequency, intensity, and duration cannot be relied upon as measures of progression in labor nor as indices of normality. Except for cervical dilatation and fetal decent, none of the clinical features of the parturient patient appears to be useful in assessing labor progression." Friedman sought to select criteria that would limit normal labor and thus be able to identify significant abnormalities of labor. These limits, admittedly arbitrary, appear to be logical and clinically useful. The graphic representation of labor plotting descent and dilatation against time has become known as the Friedman curve. It, or a modification of it, is used extensively to evaluate laboring patients.

Figure 2. Graphic portrayal of the relationship between cervical dilatation and elapsed time in labor (heavy line) and between fetal station and time (light line). Labor has been divided functionally into a preparatory division (including latent and acceleration phases of the dilatation curve), a dilatational division comprising only the linear phase of maximum slope of dilatation, and a pelvic division encompassing the linear phase of maximum descent.

Three stages of labour

• First: from the onset of labour to full dilatation (commonly lasts 8-12 hours in a first labour, 3-8 hours in subsequent labours)
• Second: from full dilatation of the cervix to delivery of the baby (commonly lasts 1-2 hours in a first labour, 0.5-1 hour in subsequent labours)
• Third: from delivery of the baby to the delivery of the placenta (commonly lasts up to an hour if physiological, 5-15 minutes if actively managed)