Cesarean section before the onset of labor and subsequent motor function in infants with meningomyelocele diagnosed antenatally Background. Meningomyelocele can now be detected before birth. Few data are available on its natural history, however, and optimal management at the time of delivery is controversial, although it has been suggested that labor and vaginal delivery may cause pressure on exposed nerve roots, resulting in additional loss of neural function. Methods. To assess the effect of labor and the type of delivery on the level of motor function in fetuses with uncomplicated meningomyelocele, we identified 200 cases of this disorder, accounting for 95 percent of the cases that occurred in the state of Washington during our 10-year study period. We compared the outcomes of 47 infants delivered by cesarean section before labor began, 35 delivered by cesarean section after a period of labor, and 78 who were delivered vaginally (another 40 were ineligible for the study). In cases of meningomyelocele detected prenatally, cesarean section was performed before the onset of labor if isolated meningomyelocele without severe hydrocephalus was present. The infants delivered in this manner were compared with those who were delivered either vaginally or by cesarean section after labor began. Results. At two years of age, the infants who had been exposed to labor were 2.2 times more likely to have severe paralysis than those delivered by cesarean section without labor (95 percent confidence interval, 1.7 to 2.8). Infants delivered by cesarean section before the beginning of labor had a mean (+/- SD) level of paralysis 3.3 +/- 3.0 segments below the anatomical level of the spinal lesion at two years of age, as compared with 1.1 +/- 2.3 for infants delivered vaginally and 0.9 +/- 4.1 for infants delivered by cesarean section after the beginning of labor (P less than 0.001 for both comparisons). Exposure to labor did not affect the frequency of neonatal complications or later intellectual performance. Conclusions. For the fetus with uncomplicated meningomyelocele, delivery by cesarean section before the onset of labor may result in better subsequent motor function than vaginal delivery or delivery by cesarean section after a period of labor. 