While in most instances there is sufficient reserve to maintain oxygenation
of the fetus during the second stage of labor even though the
uteroplacental circulation is reduced, in some circumstances both the
fetal and maternal condition can deteriorate rapidly. Deterioration can
occur both in pregnancies with known complications, such as
pre-eclampsia or intrauterine growth restriction, but also unpredictably
in low-risk pregnancies [1]. Thus, antenatal risk assessment and the status
in the first stage of labor, such as represented by a normal
partogram, are not reliable predictors of normal outcomes. Important
potential complications arising in the second stage of labor are fetal
hypoxia and acidemia leading to “birth asphyxia,” failure of the
presenting part to rotate or descend appropriately leading to obstructed
labor, and worsening or new manifestations of maternal hypertension
leading to eclampsia. Mothers with pre-existing cardiac disease or severe
anemia may be at risk of heart failure during the second stage
owing to the additional circulatory demands of active pushing.