Why some women need a D&X, a.k.a. partial birth abortion.

About 5000 fetuses develop hydrocephalus each year in the U.S. This is not usually discovered until late in the second trimester. Some cases are not severe. After birth, shunts can be installed to relieve the excess fluid on the newborn's brain. A pre-natal method of removing the excess fluid is being experimentally evaluated. However, some cases are much more serious. "It is not unusual for the fetal head to be as large as 50 centimeters (nearly 20 inches) in diameter and may contain...close to two gallons of cerebrospinal fluid." In comparison, the average adult skull is about 7 to 8 inches in diameter. A fetus with severe hydrocephalus is alive, but as a newborn cannot live for long; it cannot achieve consciousness. The physician may elect to perform a D&X by draining off the fluid from the brain area, collapsing the fetal skull and withdrawing the dead fetus. Or, he might elect to perform a type of caesarian section. The former kills a fetus before birth; the latter allows the newborn to die after birth, on its own. A caesarian section is a major operation. It does expose the woman to a greatly increased chance of infection. It "poses its own dangers to a woman and any future pregnancies." Allowing a woman to continue in labor with a severely hydrocephalic fetus is not an option; an attempted vaginal delivery would kill her and the fetus.