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Abstract
Induction of labor is the artificial initiation of uterine contraction
prior to their spontaneous onset leading to progressive dilatation and
effacement of the cervix and delivery of the baby. The term usually
restricted to pregnancies at gestations greater than the legal definition of
the fetal viability.
The rate of induction varies widely in different countries and units
and between individual obstetricians within the same unit. Such variation
may be due to differences in the indications for induction, definitions
(e.g. post maturity or hypertension) at availability of resources as well as
unexplained differences in opinion and practice. Post-term presence is the
most common indication for induction.
Prolonged pregnancy carries many problems for pregnancy, labor
and fetal outcome, namely; oligohydramniosm which may be indicator of a poor placental reserve, meconium stained liquor with the potential
danger of meconium aspiration post-partum macrosomia with shoulder
dystocia with the possibility of obstructed labor, fetal distress during
labor and increased preinatal morbidity and mortality.
Constituents of the cervix important in cervical modifications at
parturition are those in the extracellular matrix and ground substance, the glycosaminoglycans, dermatan sulfate and hyaluronic acid.
Cervical softening is associated with two complementary changes;
collagen breakdown and rearrangement of collagen fibers; and alterations
in the relative amounts of various glycosaminoglycans. Hyaluronic acid is
associated with the capacity of a tissue to retain water. Near term, there is a striking increase in the relative amount of hyaluronic acid in the cervix, with a concomitant decrease in dermatan sulfate. The role of smooth
muscle in cervical softening process is not clear.
The scoring system that has become most prevalent is the Bishop score. This system and its modifications take into account the dilation, effacement, consistency, and position of the cervix in addition to the station of the presenting part. Many have evaluated and confirmed the validity of the Bishop score. Among the factors considered in assigning the score, the strongest association with successful labor seems to be with cervical dilation.
The Bishop score has been criticized for not attributing more significance to cervical dilation. However, despite this criticism, none of the modifications to the original scoring system have been shown to improve predictability. Bishop score has a poor predictive value for the induction of labor. It was found that among the Bishop score components only dilatation and length (effacement) have shown a significant correlation with successful vaginal delivery.