Stage 2 begins with complete cervical dilation and ends with delivery of the
fetus. Its purpose is descent of the fetus through the birth canal.
Stage 3 begins with delivery of the fetus and ends with expulsion of the
placenta. The mechanism of placental separation from the uterine wall is
dependent on myometrial contractions shearing off the anchoring villi. This is
usually augmented with IV oxytocin infusion.
Active phase begins with cervical dilation acceleration ending with complete
cervical dilation. Cervical dilation of 6 cm should be considered the threshold
for active phase.
Cardinal movements of labor occur, with beginning descent of the
fetus in the latter part of this phase.
Slow but progressive labor in first stage of labor is normal and
should not be indication for cesarean delivery.
Main abnormality is arrest of active phase (reserve this diagnosis for
women ≥6 cm of dilation with ruptured membranes who show no cervical
change despite 4 h of adequate uterine activity or ≥6 h of oxytocin
administration with inadequate uterine activity).Whereas in stage 1 uterine contractions are the only force that acts on
cervical dilation, in stage 2 maternal pushing efforts are vitally important to
augment the uterine contractions to bring about descent of the fetal presenting
part.
No absolute maximum length of time spent in stage 2 of labor, after which all
women should undergo operative delivery, has been identified.
Main abnormality is prolonged second stage.
Duration of stage 2 may be up to 3 h in a primipara (4 h with epidural) or 2 h
in a multipara (3 h with epidural).